Question 1

A 45-year-old female presents with persistent, deep right shoulder pain. Radiographs reveal a 5 cm radiolucent lesion with stippled calcifications in the proximal humerus. MRI shows endosteal scalloping involving 80% of the cortical thickness. What is the most likely diagnosis?

Explanation

Endosteal scalloping greater than two-thirds of the cortical thickness and the presence of pain in a large proximal long bone lesion strongly suggest low-grade chondrosarcoma over an enchondroma.

Question 2

A 22-year-old man presents with a painless lump on his proximal humerus. Radiographs show a surface lesion with underlying cortical saucerization and a sclerotic margin.

Histology shows lobules of hyaline cartilage. What is the most appropriate management?

Explanation

The clinical, radiographic, and histologic findings are diagnostic of a periosteal chondroma, a benign cartilage tumor. Asymptomatic lesions can be safely managed with observation.

Question 3

A 30-year-old mechanic sustains a closed fracture of the proximal phalanx of the index finger after a minor trauma. Radiographs reveal a central, lytic lesion with thin cortices and a non-displaced pathologic fracture.

What is the recommended treatment plan?

Explanation

Enchondromas of the hand commonly present with pathologic fractures. The standard of care is to allow the fracture to heal with immobilization, followed by definitive curettage and bone grafting.

Question 4

A 15-year-old female presents with multiple asymmetrical bone deformities and several soft-tissue hemangiomas with phleboliths. Which of the following gene mutations is most strongly associated with this patient's underlying condition?

Explanation

Maffucci syndrome is characterized by multiple enchondromatosis and soft-tissue hemangiomas. Both Ollier disease and Maffucci syndrome are driven by somatic mosaic mutations in the IDH1 or IDH2 genes.

Question 5

A 16-year-old male is diagnosed with an osteoblastic osteosarcoma of the distal femur. What is the most sensitive imaging modality for detecting 'skip metastases' within the same bone?

Explanation

T1-weighted MRI of the entire involved bone is the gold standard for identifying skip metastases in osteosarcoma. Their presence significantly alters surgical planning and worsens the prognosis.

Question 6

A 40-year-old male presents with hip pain. Radiographs demonstrate a lytic lesion in the proximal femoral epiphysis. Biopsy reveals abundant cells with distinct borders, clear cytoplasm, and central nuclei scattered among hyaline cartilage. What is the most appropriate treatment?

Explanation

Clear cell chondrosarcoma typically presents in the epiphysis of long bones in adults. It is a low-to-intermediate grade malignant tumor that requires wide surgical resection to minimize the high risk of local recurrence.

Question 7

A 35-year-old female presents with a painless, palpable mass on her right index finger. Radiographs reveal a centrally located lytic lesion with stippled calcifications and mild cortical expansion in the proximal phalanx.

What is the most likely diagnosis?

Explanation

Enchondroma is the most common primary bone tumor in the hand, typically presenting as a centrally located lytic lesion with stippled calcifications and endosteal scalloping. They are benign, cartilage-forming tumors that often remain asymptomatic unless complicated by a pathologic fracture.

Question 8

A 24-year-old male presents with localized, dull ache over his proximal humerus. Imaging demonstrates a surface-based lesion with a sclerotic margin and 'saucerization' of the underlying outer cortex, with no medullary extension.

What is the most likely diagnosis?

Explanation

Periosteal chondromas are benign surface tumors of cartilage that characteristically produce saucerization (a well-defined cortical depression) with a sclerotic rim. Unlike osteochondromas, they do not show medullary continuity.

Question 9

A 16-year-old boy who underwent wide resection and chemotherapy for distal femoral osteosarcoma 2 years ago now presents with two new, isolated 1.5 cm nodules in the right lung base. Staging shows no other sites of disease. What is the standard of care for these lesions?

Explanation

Pulmonary metastasectomy is the gold standard for isolated, resectable lung metastases in osteosarcoma patients. Complete surgical resection of all metastatic deposits offers the best chance for long-term survival.

Question 10

A 12-year-old girl is evaluated for multiple bony deformities. Radiographs reveal numerous enchondromas throughout the appendicular skeleton. Physical examination shows multiple bluish, soft-tissue masses on her limbs consistent with hemangiomas. Which syndrome does this patient have?

Explanation

Maffucci syndrome is characterized by the presence of multiple enchondromas (enchondromatosis) and soft-tissue hemangiomas. Patients with Maffucci syndrome carry a significantly higher risk of malignant transformation to chondrosarcoma (up to 100% over a lifetime) compared to Ollier disease.

Question 11

Recent genomic profiling has identified specific somatic mutations that are highly prevalent in solitary enchondromas, central chondrosarcomas, and syndromic enchondromatosis. Which of the following mutations is most characteristically involved?

Explanation

Mutations in the isocitrate dehydrogenase genes (IDH1 and IDH2) are found in the vast majority of enchondromas and central chondrosarcomas. They result in the production of an oncometabolite, 2-hydroxyglutarate, which alters cellular epigenetics.

Question 12

A 55-year-old male presents with deep, progressive shoulder pain. Radiographs show a cartilaginous lesion in the proximal humerus. Which of the following MRI findings most strongly supports a diagnosis of high-grade chondrosarcoma over a benign enchondroma?

Explanation

Deep endosteal scalloping (>2/3 of cortical thickness), cortical breakthrough, and soft tissue extension are hallmark imaging signs of malignant transformation to chondrosarcoma. Enchondromas typically display minimal endosteal scalloping.

Question 13

A 15-year-old male complains of chronic knee pain. Radiographs reveal an eccentric, lytic lesion in the distal femoral epiphysis that crosses an open physis. Histology shows polygonal cells with grooved nuclei and fine, pericellular calcifications. What is the diagnosis?

Explanation

Chondroblastoma characteristically occurs in the epiphysis or apophysis of young patients. Histologic hallmarks include mononuclear chondroblasts with grooved nuclei (coffee bean appearance) and pericellular 'chicken-wire' calcification.

Question 14

A 22-year-old male presents with a localized, painful swelling on the distal humerus. Imaging confirms a surface cartilaginous lesion.

Biopsy confirms a benign hyaline cartilage tumor. What is the most appropriate management?

Explanation

For symptomatic periosteal chondromas, the treatment of choice is marginal excision, which should include the underlying saucerized sclerotic cortex to minimize recurrence risk. Wide resection is unnecessary for these benign lesions.

Question 15

A 40-year-old male presents with a lytic lesion in the proximal femoral epiphysis. Biopsy reveals cells with abundant clear cytoplasm and distinct boundaries in a background of hyaline cartilage and reactive bone. What is the recommended treatment for this lesion?

Explanation

Clear cell chondrosarcoma is a low-grade malignant tumor that uniquely favors the epiphysis, often mimicking chondroblastoma. The standard of care is wide en bloc resection, as intralesional procedures carry an unacceptably high recurrence rate.

Question 16

A 30-year-old male is diagnosed with synovial sarcoma of the distal thigh. Following wide local excision, he is monitored for distant metastasis. What is the most common site of metastasis for this tumor?

Explanation

The lungs are the most common site of distant metastasis for nearly all high-grade soft tissue sarcomas of the extremities, including synovial sarcoma. Surveillance imaging must routinely include non-contrast chest CT.

Question 17

Which histologic feature is the hallmark of dedifferentiated chondrosarcoma?

Explanation

Dedifferentiated chondrosarcoma is characterized by a bimorphic histologic pattern showing an abrupt transition between a low-grade cartilage tumor and a high-grade, non-cartilaginous sarcoma (e.g., osteosarcoma, fibrosarcoma). It carries a very poor prognosis.

Question 18

A 20-year-old female presents with an eccentric, multiloculated, lytic lesion with a sclerotic rim in the proximal tibial metaphysis. Biopsy shows stellate and spindle cells in a myxoid background with scattered osteoclast-like giant cells. What is the most likely diagnosis?

Explanation

Chondromyxoid fibroma (CMF) classically presents as an eccentric, lytic metaphyseal lesion with a sclerotic rim. Histologically, it demonstrates lobules of stellate/spindle cells in a myxoid background, often with giant cells at the lobular peripheries.

Question 19

A 30-year-old patient presents with acute finger pain after minor trauma. Imaging shows a pathologic fracture through a central, lytic lesion with faint calcification.

What is the most appropriate initial management?

Explanation

When a patient presents with a pathologic fracture through an enchondroma in the hand, the initial treatment is non-operative immobilization to allow the fracture to heal. Once healed, intralesional curettage and bone grafting can be safely performed.

Question 20

A 14-year-old girl is diagnosed with a conventional high-grade intramedullary osteosarcoma of the distal femur. What is the standard neoadjuvant chemotherapy regimen utilized to improve survival and prevent metastasis?

Explanation

The standard of care for high-grade osteosarcoma is the 'MAP' regimen, consisting of high-dose Methotrexate, Adriamycin (Doxorubicin), and Cisplatin. This regimen significantly improves long-term survival by eradicating micrometastatic disease.

Question 21

A 10-year-old boy presents with a permeative lesion in the femoral diaphysis and an 'onion-skin' periosteal reaction. Molecular testing of the biopsy specimen is most likely to reveal which of the following chromosomal translocations?

Explanation

Ewing sarcoma is classically associated with the t(11;22)(q24;q12) translocation, leading to the EWSR1-FLI1 fusion gene. This drives the pathogenesis of the small round blue cell tumor.

Question 22

Mesenchymal chondrosarcoma is a rare, aggressive bone tumor. Which of the following characteristics is true regarding its clinical behavior?

Explanation

Mesenchymal chondrosarcoma is an aggressive variant known for its bimorphic histology (small round blue cells and cartilage islands) and a high propensity for late metastasis, often recurring or metastasizing a decade or more after initial therapy.

Question 23

A 60-year-old man had a wide local excision and radiation for a high-grade undifferentiated pleomorphic sarcoma of the thigh 18 months ago. Routine surveillance CT reveals an isolated 2 cm metastasis in the left lower pulmonary lobe. What is the most appropriate treatment recommendation?

Explanation

For soft tissue sarcoma patients presenting with isolated, resectable pulmonary metastasis (with no extrapulmonary disease and control of the primary site), pulmonary metastasectomy provides the best chance for extended survival.

Question 24

A 26-year-old woman is evaluated for a localized mass on the surface of her proximal tibia. Radiographs reveal saucerization of the underlying cortex and a sclerotic margin.

Which radiographic feature best differentiates this lesion from a periosteal osteosarcoma?

Explanation

Periosteal chondroma typically causes saucerization (a scallop/depression) of the underlying cortex with a thickened sclerotic rim. In contrast, periosteal osteosarcoma typically shows aggressive perpendicular new bone formation (sunburst) without the mature sclerotic rim.

Question 25

A 45-year-old asymptomatic woman undergoes knee radiography for mild osteoarthritis. An incidental 3-cm lobulated, calcified metaphyseal lesion is found in the distal femur. MRI demonstrates lobular hyperintensity on T2-weighted images without cortical breakthrough or soft tissue extension. Which genetic mutation is most commonly associated with this specific tumor's pathogenesis?

Explanation

Enchondromas and chondrosarcomas are frequently associated with somatic mutations in isocitrate dehydrogenase 1 and 2 (IDH1/IDH2). EXT mutations are seen in osteochondromas, while GNAS1 is associated with fibrous dysplasia.

Question 26

A 16-year-old boy presents with a painless lump on his proximal humerus. Radiographs reveal a surface lesion causing 'saucerization' of the underlying cortex with a well-defined sclerotic margin and stippled calcifications.

What is the most appropriate initial management for this lesion if it remains asymptomatic?

Explanation

The clinical and radiographic presentation is classic for a periosteal chondroma, a benign surface cartilage tumor. Asymptomatic periosteal chondromas can be managed with observation and serial radiographs.

Question 27

A 30-year-old male with Maffucci syndrome presents with increasing pain in his distal femur. Radiographs show a previously calcified enchondroma that now exhibits cortical destruction and a soft-tissue mass. Which of the following systemic malignancies is this patient at highest risk for compared to a patient with Ollier disease?

Explanation

Maffucci syndrome (multiple enchondromas and soft-tissue hemangiomas) carries an exceptionally high risk of malignant transformation, not only to chondrosarcoma but also to systemic malignancies like gastrointestinal adenocarcinomas and brain tumors (astrocytomas). This distinguishes its systemic risk profile from Ollier disease.

Question 28

A 14-year-old girl is diagnosed with high-grade conventional osteosarcoma of the distal femur. She completes neoadjuvant chemotherapy and undergoes surgical resection. Pathological analysis of the resected specimen reveals 95% tumor necrosis. What is the most significant clinical implication of this finding?

Explanation

Tumor necrosis greater than 90% following neoadjuvant chemotherapy (Huvos Grade III or IV) is the most powerful predictor of long-term survival in localized osteosarcoma. Adjuvant chemotherapy is still indicated.

Question 29

A 22-year-old man presents with acute pain and swelling in his index finger after a minor fall. Radiographs demonstrate a pathologic fracture through a central, lytic, expansile lesion with stippled calcification in the proximal phalanx.

What is the recommended management?

Explanation

Enchondroma is the most common primary bone tumor of the hand. When presenting with a pathologic fracture, the standard treatment is to allow the fracture to heal first, followed by definitive curettage and bone grafting to prevent recurrence.

Question 30

Which of the following radiographic features best differentiates a low-grade chondrosarcoma from a benign enchondroma in a long bone?

Explanation

While both enchondromas and low-grade chondrosarcomas exhibit cartilage matrix ('rings and arcs') and high T2 MRI signal, deep endosteal scalloping (>2/3 cortical thickness) is a hallmark of aggressive behavior favoring chondrosarcoma. Pain independent of mechanical causes also strongly suggests malignancy.

Question 31

A 17-year-old male with classic Ewing sarcoma of the diaphyseal femur undergoes initial staging. Which of the following sites is the most common location for metastasis in this disease, and what specific staging test is uniquely mandatory compared to osteosarcoma?

Explanation

The lungs are the most common site of metastasis for Ewing sarcoma, followed by bone and bone marrow. A bone marrow aspirate and biopsy are mandatory parts of the initial staging for Ewing sarcoma, unlike osteosarcoma.

Question 32

A 65-year-old male with a long-standing, stable calcified lesion in his proximal humerus presents with sudden, rapidly progressive pain and a palpable soft tissue mass. Biopsy reveals a biphasic tumor with regions of low-grade hyaline cartilage adjacent to a high-grade undifferentiated spindle cell sarcoma. What is the diagnosis?

Explanation

Dedifferentiated chondrosarcoma is characterized by a bimorphic histologic pattern showing a low-grade chondroid tumor abruptly transitioning into a high-grade, non-cartilaginous sarcoma. It carries a very poor prognosis.

Question 33

A 40-year-old female presents with shoulder pain. Radiographs reveal a purely lytic lesion confined to the epiphysis of the proximal humerus. Histology demonstrates cells with abundant clear cytoplasm, distinct borders, and scattered multinucleated giant cells within a cartilaginous background. What is the most likely diagnosis?

Explanation

Clear cell chondrosarcoma typically presents as a lytic lesion in the epiphysis of long bones (often proximal femur or humerus) in adults. Chondroblastoma also occurs in the epiphysis but usually in younger, skeletally immature patients.

Question 34

During the surgical planning for a patient with high-grade osteosarcoma of the distal femur, an MRI of the entire femur is obtained. The primary purpose of imaging the entire bone is to evaluate for which of the following?

Explanation

Whole-bone MRI is essential in the staging of osteosarcoma and Ewing sarcoma to detect skip metastases (tumors within the same bone separated from the primary lesion by normal marrow). Their presence upgrades the tumor to Stage III and necessitates a broader resection or total bone replacement.

Question 35

A 21-year-old patient who underwent distal femoral replacement for osteosarcoma 2 years ago presents for follow-up. A routine chest CT shows a solitary 1.5 cm peripheral nodule in the right lower lobe. The primary tumor site is free of recurrence, and no other lesions are noted. What is the most appropriate next step in management?

Explanation

In osteosarcoma patients with isolated, completely resectable pulmonary metastases and a controlled primary tumor, surgical metastasectomy offers the best chance for prolonged survival and potential cure.

Question 36

A 35-year-old male undergoes a radiograph for knee pain. A surface lesion is noted on the distal femur. Biopsy reveals intermediate-grade malignant cells producing a predominantly cartilaginous matrix with some osteoid, situated on the cortical surface without medullary involvement. The radiographic appearance shows a 'sunburst' periosteal reaction. What is the diagnosis?

Explanation

Periosteal osteosarcoma is typically an intermediate-grade surface tumor with a chondroblastic matrix, often presenting with a 'sunburst' periosteal reaction. Parosteal osteosarcoma is low-grade, heavily ossified, and typically located on the posterior distal femur.

Question 37

A 50-year-old male presents with a destructive bone lesion in the pelvis. A biopsy is planned. Before performing a biopsy on a suspected metastatic lesion of unknown primary origin, what is the most critical initial diagnostic step?

Explanation

Before biopsying a suspected metastasis, complete staging is required. This identifies the primary tumor, locates potentially safer or more accessible biopsy sites, and rules out highly vascular tumors (e.g., renal cell or thyroid carcinoma) that require pre-biopsy embolization.

Question 38

An MRI of the knee in a 40-year-old woman shows a medullary lesion in the distal femur. The radiologist notes a 'double-line sign' on T2-weighted images and a serpiginous border, distinguishing it from an enchondroma. What is the most likely diagnosis?

Explanation

The 'double-line sign' on T2 MRI (inner high signal of granulation tissue, outer low signal of sclerosis) and a serpiginous border are classic imaging hallmarks of a bone infarct, differentiating it from the lobular hyperintensity of an enchondroma.

Question 39

A 28-year-old man presents with a small, palpable mass on his proximal tibia. Radiographs show a well-circumscribed, saucer-like cortical depression with a sclerotic rim.

Histology shows benign hyaline cartilage. Which characteristic best differentiates this from an osteochondroma?

Explanation

Periosteal chondromas are surface lesions that arise under the periosteum and erode the outer cortex (saucerization). Unlike osteochondromas, they do not exhibit continuity with the medullary canal of the host bone.

Question 40

A 30-year-old woman presents with jaw pain. Imaging reveals a destructive lesion in the mandible. Histology displays a biphasic pattern with islands of well-differentiated hyaline cartilage surrounded by sheets of small, undifferentiated round blue cells in a hemangiopericytoma-like vascular pattern. What is the diagnosis?

Explanation

Mesenchymal chondrosarcoma features a distinct biphasic histology: islands of benign-appearing cartilage mixed with highly cellular areas of small round blue cells. It frequently occurs in the jaw, ribs, or extraskeletal sites.

Question 41

In a 15-year-old male with osteosarcoma of the proximal tibia, which of the following findings would upstage the patient to Stage III according to the Enneking Surgical Staging System?

Explanation

In the Enneking system, Stage III denotes the presence of regional or distant metastasis. A skip metastasis (a separate tumor nodule within the same bone) is considered a regional metastasis and automatically upgrades the tumor to Stage III.

Question 42

Which of the following bone tumors characteristically expresses the t(11;22)(q24;q12) chromosomal translocation resulting in the EWS-FLI1 fusion protein?

Explanation

Ewing sarcoma is defined molecularly by the t(11;22) translocation, which fuses the EWSR1 gene on chromosome 22 with the FLI1 gene on chromosome 11. Synovial sarcoma has t(X;18), and myxoid liposarcoma has t(12;16).

Question 43

A patient with multiple hereditary exostoses (MHE) is monitored for malignant transformation. Which clinical or radiographic sign is the most reliable indicator of secondary chondrosarcoma arising from an osteochondroma in an adult?

Explanation

In an adult (skeletally mature) patient, an osteochondroma should not grow. New-onset pain, growth, or an MRI showing a cartilage cap greater than 1.5 to 2 cm are highly suspicious for malignant transformation to secondary chondrosarcoma.

Question 44

A 20-year-old male undergoes curettage of a lytic lesion in the proximal phalanx of the hand.

Pathological examination shows lobules of mature hyaline cartilage. Which of the following best describes the recurrence risk and malignant potential of this solitary hand lesion?

Explanation

Solitary enchondromas of the hand have a low recurrence rate after adequate intralesional curettage and grafting. Malignant transformation of a solitary enchondroma in the hand is exceedingly rare, distinguishing it from enchondromas in long bones.

Question 45

A 25-year-old female presents with multiple enchondromas and soft-tissue hemangiomas. Which genetic mutation is most strongly associated with her underlying syndrome?

Explanation

Maffucci syndrome is characterized by multiple enchondromas and soft-tissue hemangiomas. The condition is driven primarily by somatic mosaic mutations in the IDH1 or IDH2 genes.

Question 46

A 16-year-old boy presents with a painless lump on his proximal humerus. Imaging demonstrates a surface lesion causing saucerization of the underlying cortex with a sclerotic margin and cartilaginous matrix.

What is the most appropriate management for a growing, symptomatic lesion of this type?

Explanation

The image and clinical description are classic for a periosteal chondroma. Symptomatic or growing lesions are best treated with marginal excision that includes the underlying sclerotic cortex to minimize recurrence risk.

Question 47

Which of the following radiographic features is the most reliable indicator differentiating a low-grade central chondrosarcoma from a benign enchondroma in a long bone?

Explanation

Endosteal scalloping greater than two-thirds of the cortical thickness, cortical breakthrough, or soft tissue extension strongly suggests a low-grade chondrosarcoma rather than a benign enchondroma.

Question 48

A 14-year-old boy with conventional osteosarcoma of the distal femur completes neoadjuvant chemotherapy. Restaging scans show two new 1 cm peripheral lung nodules. His primary tumor is resectable. What is the most appropriate management?

Explanation

Pulmonary metastases in osteosarcoma do not preclude curative-intent surgery. Wide resection of the primary bone tumor and complete resection of pulmonary metastases offer the best chance for long-term survival.

Question 49

A 35-year-old man sustains a closed, minimally displaced fracture through a lytic lesion in the proximal phalanx of his ring finger. Radiographs show a well-circumscribed, expansile lucency with stippled calcifications.

What is the most appropriate initial management?

Explanation

The clinical scenario and image represent a pathologic fracture through an enchondroma. The standard of care is to allow the fracture to heal with immobilization, followed by intralesional curettage and bone grafting.

Question 50

A 28-year-old female presents with a solitary enchondroma of the distal femur discovered incidentally on an MRI for a knee sprain. Which of the following statements regarding solitary enchondromas is true?

Explanation

Solitary enchondromas are common benign cartilaginous tumors that often harbor somatic mutations in IDH1 or IDH2. They are typically asymptomatic and carry a very low risk of malignant transformation (<1%).

Question 51

In a patient with Ewing sarcoma, what is the most common site of metastasis at the time of initial presentation?

Explanation

The lungs are the most common site of metastasis for Ewing sarcoma at initial presentation. Bone and bone marrow are the next most common sites.

Question 52

A 45-year-old man undergoes resection of a large pelvic mass. Histopathology reveals a biphasic tumor with islands of well-differentiated, low-grade hyaline cartilage adjacent to a high-grade, non-cartilaginous spindle cell sarcoma. What is the diagnosis?

Explanation

Dedifferentiated chondrosarcoma is characterized by a biphasic histologic pattern with a sharp demarcation between a low-grade cartilage tumor and a high-grade spindle cell component. It carries a very poor prognosis.

Question 53

A 22-year-old male with Ollier disease presents with worsening pain and a rapidly enlarging mass in his proximal tibia. Which of the following is the most likely secondary malignancy to develop in this patient?

Explanation

Patients with Ollier disease (multiple enchondromatosis) have an elevated risk (approximately 25-30%) of malignant transformation. This transformation is most commonly to a secondary chondrosarcoma.

Question 54

An MRI of a patient with distal femoral osteosarcoma reveals a distinct, separate tumor focus within the proximal medullary canal of the same bone. What term best describes this finding, and how does it affect surgical planning?

Explanation

A skip metastasis is a separate focus of tumor within the same bone or transarticular. Its presence dictates a broader resection, often requiring whole-bone resection or a significantly higher amputation level to achieve negative margins.

Question 55

A 19-year-old female presents with a small (< 2 cm), painless cartilaginous lesion on the surface of the proximal humerus cortex.

Histologically, it shows hypercellularity and binucleate cells. What clinical or radiographic feature distinguishes this periosteal chondroma from a periosteal chondrosarcoma?

Explanation

Periosteal chondromas often exhibit hypercellularity and atypia mimicking malignancy. They are distinguished from periosteal chondrosarcomas primarily by their small size (< 3 cm) and lack of soft tissue invasion.

Question 56

Which of the following characteristics is most suggestive of clear cell chondrosarcoma?

Explanation

Clear cell chondrosarcoma is a low-grade malignant cartilage tumor that characteristically arises in the epiphysis of long bones in adults. Because of its epiphyseal location, it can sometimes radiographically mimic a chondroblastoma.

Question 57

A 60-year-old man presents with a painful lesion in the diaphysis of the femur. Biopsy reveals small blue round cells mixed with islands of benign-appearing cartilage and a hemangiopericytoma-like vascular pattern (staghorn vessels). What is the most likely diagnosis?

Explanation

Mesenchymal chondrosarcoma is a rare, aggressive tumor characterized histologically by a bimorphic pattern of highly cellular small round blue cells and islands of well-differentiated hyaline cartilage with branching staghorn vessels.

Question 58

A 55-year-old woman is incidentally found to have a 3 cm enchondroma in her proximal humerus. Radiographs show classic rings and arcs calcification. She is completely asymptomatic. What is the most appropriate management?

Explanation

Asymptomatic enchondromas discovered incidentally in adults without aggressive radiographic features should be managed with serial observation. This monitors for any pain or radiographic changes suggesting malignant transformation.

Question 59

Regarding survival in patients with osteosarcoma who develop pulmonary metastases, which factor is most strongly associated with improved long-term outcomes?

Explanation

The most significant prognostic factor for long-term survival in osteosarcoma patients with pulmonary metastases is the ability to achieve complete surgical resection of all metastatic lung lesions (metastasectomy).

Question 60

A 30-year-old male has an expansile lucent lesion in the proximal phalanx of the index finger.

A biopsy confirms enchondroma. During surgical treatment, what is the most important intraoperative step to minimize the risk of local recurrence?

Explanation

In the treatment of enchondromas of the hand, thorough intralesional curettage supplemented with high-speed mechanical burring of the cavity walls is critical to remove microscopic tumor extensions and minimize local recurrence.

Question 61

What is the primary role of whole-lung irradiation in the treatment of Ewing sarcoma?

Explanation

Whole-lung irradiation is often incorporated into the treatment protocol for patients with Ewing sarcoma who present with pulmonary metastases. It has been shown to improve event-free and overall survival in this metastatic cohort.

Question 62

A 35-year-old male presents with a painless lump in his hand after a minor bump. Radiographs show a well-circumscribed, lytic lesion in the proximal phalanx with stippled calcifications.

What is the most appropriate management for a confirmed non-pathologic, asymptomatic enchondroma in this location?

Explanation

Asymptomatic enchondromas in the hand without impending fracture are generally observed. If a pathologic fracture occurs, the fracture is allowed to heal before curettage and grafting are considered.

Question 63

A 22-year-old female presents with multiple asymmetrical cartilaginous lesions in her long bones and hands, associated with soft-tissue hemangiomas. Which of the following genetic mutations is most characteristic of her underlying syndrome?

Explanation

This patient has Maffucci syndrome, characterized by multiple enchondromas and soft-tissue hemangiomas. Both Ollier disease and Maffucci syndrome are frequently associated with somatic mutations in the IDH1 or IDH2 genes.

Question 64

A 24-year-old male presents with a mildly painful palpable mass on the proximal humerus. Radiographs reveal a surface lesion with cortical saucerization and a sclerotic periosteal reaction at the proximal and distal margins.

What is the most likely diagnosis?

Explanation

Periosteal chondromas typically present in young adults as surface lesions causing saucerization of the underlying cortex with a sclerotic margin. They are usually less than 3 cm in size and lack medullary involvement.

Question 65

In a 15-year-old male diagnosed with high-grade intramedullary osteosarcoma of the distal femur, what is the most significant prognostic factor for overall survival at the time of presentation?

Explanation

The presence of macroscopic pulmonary metastases at presentation is the most critical adverse prognostic factor for overall survival in osteosarcoma. Tumor necrosis following neoadjuvant chemotherapy is the best predictor of event-free survival post-treatment.

Question 66

A 45-year-old patient with a known distal femur enchondroma presents with new-onset, deep, dull aching pain at night. Radiographs show increased endosteal scalloping.

Which radiographic feature is most indicative of malignant transformation to a low-grade chondrosarcoma?

Explanation

Malignant transformation of an enchondroma to a low-grade chondrosarcoma is suggested by deep endosteal scalloping involving more than 2/3 of the cortical thickness, new-onset pain, or cortical breakthrough. Popcorn calcifications are a feature of cartilaginous tumors generally, not specific for malignancy.

Question 67

A 28-year-old female presents with a growing, tender mass on her anterior tibia. Biopsy confirms a periosteal chondroma. The lesion measures 2.5 cm. What is the recommended treatment?

Explanation

For a symptomatic or growing periosteal chondroma, the recommended treatment is marginal excision, removing the tumor along with its underlying sclerotic bony base. This ensures a low risk of local recurrence.

Question 68

A 17-year-old male with a history of distal femur osteosarcoma, treated with wide resection and chemotherapy two years ago, presents with a solitary 1.5 cm pulmonary metastasis. The primary site has no local recurrence. What is the most appropriate management?

Explanation

Surgical resection (metastasectomy) of pulmonary metastases in osteosarcoma provides a significant survival benefit when the primary tumor is controlled and the lung lesions are completely resectable. It is the standard of care for isolated, resectable pulmonary relapses.

Question 69

A 40-year-old male complains of chronic hip pain. Radiographs reveal an epiphyseal lytic lesion in the proximal femur with a sclerotic margin and central calcifications. What is the most likely diagnosis, considering this distinct epiphyseal location in an adult?

Explanation

Clear cell chondrosarcoma typically presents as a lytic epiphyseal lesion in adults (30-50 years old), often mimicking a chondroblastoma, which typically occurs in skeletally immature patients. It requires wide surgical resection due to its low-grade malignant potential.

Question 70

A 12-year-old boy presents with multiple cartilaginous lesions in the hands and long bones, accompanied by distinct soft-tissue masses with phleboliths noted on radiographs. What is the most significant long-term risk associated with his underlying syndrome?

Explanation

The patient has Maffucci syndrome, characterized by multiple enchondromas and soft-tissue hemangiomas. Unlike Ollier disease, patients with Maffucci syndrome have a near 100% risk of malignant transformation, most commonly to chondrosarcoma or visceral malignancies.

Question 71

An asymptomatic 35-year-old woman has a hand radiograph taken after a minor sprain, revealing the lesion shown.

Recent molecular studies show that solitary lesions of this type are most strongly associated with somatic mutations in which of the following genes?

Explanation

The image shows a solitary enchondroma, characterized by a central radiolucent lesion with stippled calcifications. Somatic mutations in IDH1 and IDH2 are found in the vast majority of solitary enchondromas and central chondrosarcomas.

Question 72

A 24-year-old male presents with a painless palpable mass on the proximal humerus. Radiographs show a surface-based radiolucent lesion with a well-defined sclerotic border and overhanging cortical edges. Which of the following radiographic features best differentiates this lesion from a juxtacortical (periosteal) chondrosarcoma?

Explanation

Periosteal chondromas are benign surface lesions that are typically smaller than 3 cm with a sclerotic margin. Periosteal chondrosarcomas present similarly but are usually larger than 3-5 cm and may lack a distinct sclerotic cortical margin.

Question 73

A 15-year-old girl is undergoing post-treatment surveillance following wide resection and neoadjuvant chemotherapy for conventional osteosarcoma of the distal femur. What is the most common site of metastasis for this tumor and the primary imaging modality for surveillance?

Explanation

The lungs are the most common site of metastasis for osteosarcoma. Non-contrast CT of the chest is the gold standard for detecting pulmonary metastases during post-treatment surveillance.

Question 74

A 55-year-old man undergoes a biopsy of a large destructive pelvic mass. Histopathology reveals Grade 2 conventional chondrosarcoma. Staging studies are negative for metastasis. What is the most appropriate primary treatment?

Explanation

Conventional chondrosarcomas (Grades 2 and 3) are notoriously resistant to both chemotherapy and radiation therapy. Wide surgical resection is the standard of care for curative intent.

Question 75

A 40-year-old man with Multiple Hereditary Exostoses presents with a newly enlarging mass on his right posterior distal femur. MRI reveals an exophytic bone lesion with an overlying hyperintense cartilaginous cap on T2-weighted images. What cartilage cap thickness is highly suspicious for secondary malignant transformation?

Explanation

In adults, an osteochondroma cartilage cap thickness greater than 2 cm on MRI is highly suspicious for secondary malignant transformation to a peripheral chondrosarcoma.

Question 76

A 42-year-old woman presents with persistent hip pain. Radiographs demonstrate an expansile, lytic epiphyseal lesion in the proximal femur with sharp margins. Histologic evaluation shows cells with abundant clear cytoplasm and distinct cell membranes intermixed with areas of reactive bone formation. What is the most likely diagnosis?

Explanation

Clear cell chondrosarcoma classically presents as an epiphyseal lytic lesion in adults (typically older than those with chondroblastomas). The presence of clear cytoplasm and reactive bone is a histologic hallmark.

Question 77

A 14-year-old boy is diagnosed with Ewing sarcoma of the femoral diaphysis. Staging is performed. The presence of metastasis at diagnosis is the most significant negative prognostic factor. Which of the following are the two most common sites of metastasis for this disease?

Explanation

Ewing sarcoma most commonly metastasizes to the lungs and to other bones/bone marrow. A thorough staging evaluation must include chest CT and a bone marrow aspirate/biopsy or PET-CT.

Question 78

A 65-year-old male presents with a pathologic fracture of the humerus through a purely lytic, highly destructive lesion. Staging reveals an unknown primary tumor. Before planning an open biopsy, standard practice requires a CT of the chest, abdomen, and pelvis. Which primary carcinoma is notorious for producing highly vascular lytic metastases that may require pre-operative embolization?

Explanation

Renal cell carcinoma and thyroid carcinoma typically produce highly vascular, purely lytic bone metastases. Pre-operative embolization is often recommended prior to biopsy or stabilization to prevent massive hemorrhage.

Question 79

A 60-year-old woman presents with thigh pain. Radiographs show a centrally located lesion in the distal femur with rings and arcs of calcification, alongside a large, destructive, purely lytic unmineralized mass breaching the cortex. Biopsy confirms a bimorphic histologic pattern. What is this entity?

Explanation

Dedifferentiated chondrosarcoma is defined by the juxtaposition of a low-grade cartilage tumor with a high-grade spindle cell sarcoma (such as osteosarcoma, fibrosarcoma, or UPS). It portends a very poor prognosis.

Question 80

A 20-year-old male presents with chronic knee pain. Imaging reveals an eccentric, purely lytic lesion in the proximal tibial metaphysis with a well-demarcated sclerotic margin. Histology shows lobules of stellate and spindle-shaped cells in a myxoid background, with an increased concentration of cells at the periphery of the lobules. What is the diagnosis?

Explanation

Chondromyxoid fibroma classically presents as an eccentric metaphyseal lytic lesion. Histologically, it features chondroid lobules with myxoid tissue, stellate cells, and hypercellular peripheries.

Question 81

A 16-year-old female is diagnosed with osteosarcoma of the distal femur. A full-length MRI of the entire femur is ordered prior to finalizing surgical planning. What is the primary purpose of imaging the entire involved bone?

Explanation

Complete imaging of the affected bone (e.g., entire femur for a distal femur lesion) is mandatory in osteosarcoma to identify skip metastases, which are discrete medullary tumor foci separated from the primary tumor by normal marrow.

Question 82

A 32-year-old female presents with a surface-based lesion on the posterior distal femur measuring 6 cm. It lacks a sunburst appearance or medullary involvement. Biopsy reveals Grade 2 cartilaginous tissue without malignant osteoid. How does the management of this periosteal chondrosarcoma differ from that of periosteal osteosarcoma?

Explanation

Periosteal chondrosarcoma is treated primarily with wide surgical resection. Unlike high-grade surface osteosarcomas, it does not typically respond to chemotherapy and has a generally favorable prognosis with adequate surgical margins.

Question 83

A 48-year-old man presents with right shoulder pain worsened by overhead activity. Radiographs reveal an incidental 3 cm medullary lesion with stippled calcifications in the proximal humerus without cortical scalloping. A subacromial corticosteroid injection provides 100% relief of his shoulder pain. What is the next best step in management of the bone lesion?

Explanation

The lesion is a classic asymptomatic enchondroma, as the shoulder pain was proven to be mechanical (resolved via subacromial injection). The correct management for a small, asymptomatic enchondroma without aggressive features is observation with serial radiographs.

Question 84

A 35-year-old man undergoes knee arthroscopy for mechanical catching. The surgeon finds dozens of white, cartilaginous loose bodies of similar size within the joint space, and the synovium appears thickened. What is the estimated risk of malignant transformation of this condition?

Explanation

Primary synovial chondromatosis is a benign neoplastic process. The risk of malignant transformation to secondary synovial chondrosarcoma is extremely low, occurring in less than 5% of cases.

Question 85

Which of the following histologic factors correlates most strongly with long-term survival in a patient undergoing treatment for localized conventional osteosarcoma?

Explanation

The most powerful prognostic indicator for long-term survival in patients with non-metastatic osteosarcoma is the histologic response to neoadjuvant chemotherapy, specifically achieving >90% tumor necrosis (a 'good response').

Question 86

A 22-year-old patient presents with a painful mass on the proximal phalanx. Radiographs show a small saucerized surface lesion with a sclerotic margin.

Biopsy confirms a periosteal chondroma. The pain persists despite conservative measures. What is the definitive management?

Explanation

Symptomatic or enlarging periosteal chondromas are treated with en bloc marginal excision, which includes the removal of the underlying saucerized cortex, to minimize the risk of local recurrence.

Question 87

A 10-year-old child presents with a permeative lesion in the diaphysis of the fibula with an 'onion-skin' periosteal reaction. A core needle biopsy demonstrates sheets of small round blue cells. Which chromosomal translocation is the diagnostic hallmark for the most likely tumor?

Explanation

The clinical and histologic picture describes Ewing sarcoma. The diagnostic hallmark is the t(11;22)(q24;q12) translocation, which creates the EWS-FLI1 fusion protein in over 85% of cases.

Question 88

A 45-year-old woman is evaluated for a large, purely lytic sacral lesion. Biopsy shows large cells with abundant clear cytoplasm and distinct borders. Immunohistochemistry is strongly positive for cytokeratin and EMA. What is the most likely diagnosis?

Explanation

While clear cell chondrosarcoma has clear cells, the strong positivity for cytokeratin and EMA in a destructive lytic lesion highly suggests metastatic carcinoma, with renal cell carcinoma being a primary culprit for clear cell morphology. (Chordomas are midline but typified by physaliferous cells and brachyury positivity).

Question 89

A 50-year-old male is being treated for a low-grade central chondrosarcoma of the proximal femur. Which of the following imaging features on MRI is most characteristic of high-grade transformation or dedifferentiation within a pre-existing low-grade cartilage tumor?

Explanation

A classic sign of dedifferentiated chondrosarcoma on MRI is a biphasic tumor: a typical high-T2-signal cartilaginous component juxtaposed with a new, distinct unmineralized mass demonstrating lower T2 signal (representing the high-grade non-cartilaginous sarcomatous component).

Question 90

A 15-year-old female presents with multiple hard bony swellings on her hands and bluish, compressible soft tissue nodules on her forearms. Which of the following describes the underlying genetic abnormality and the estimated lifetime risk of malignant transformation in this patient?

Explanation

This patient has Maffucci syndrome, characterized by multiple enchondromas and soft tissue hemangiomas, driven by somatic mosaic mutations in IDH1 or IDH2. It carries a lifetime risk of malignant transformation (e.g., chondrosarcoma, astrocytoma) approaching 100%, far higher than Ollier disease.

Question 91

A 14-year-old boy completes neoadjuvant chemotherapy and wide resection for a distal femur osteosarcoma. Two years later, a surveillance chest CT reveals three new, unilateral peripheral lung nodules (largest 1.5 cm) with no other evidence of disease. What is the most appropriate next step in management?

Explanation

Surgical resection of isolated, completely resectable pulmonary metastases (metastasectomy) offers the best chance for prolonged survival in osteosarcoma patients. Chemotherapy may be added, but surgical removal is the cornerstone of treating limited pulmonary relapse.

Question 92

A 35-year-old male presents with chronic hip pain. Radiographs reveal a lytic lesion in the femoral head epiphysis with a sclerotic margin and central calcification. Histology shows cells with abundant clear cytoplasm and distinct cell membranes interspersed with hyaline cartilage. What is the most appropriate definitive surgical treatment?

Explanation

Clear cell chondrosarcoma is a low-grade malignancy that classically occurs in the epiphysis, mimicking benign chondroblastoma. Unlike chondroblastoma, it has a high local recurrence rate with curettage and requires wide local excision.

Question 93

A 42-year-old woman undergoes radiographs for a knee sprain, revealing an incidental finding in the distal femur:

She denies thigh pain. MRI confirms a well-circumscribed, lobulated cartilaginous lesion without endosteal scalloping or cortical breakthrough. What is the next best step in management?

Explanation

The image demonstrates a classic asymptomatic enchondroma with typical 'popcorn' calcifications. Lesions without aggressive features (like deep endosteal scalloping or pain) are benign and should be managed with clinical observation.

Question 94

A 60-year-old man presents with severe proximal thigh pain. Radiographs show a large, purely osteolytic, expansile lesion in the proximal femur with an impending subtrochanteric fracture. Biopsy confirms metastatic clear cell renal carcinoma. Before proceeding with prophylactic cephalomedullary nailing, which of the following is highly recommended?

Explanation

Renal cell carcinoma and thyroid carcinoma bone metastases are notoriously hypervascular. Preoperative angioembolization is strongly recommended 24 to 48 hours prior to surgery to minimize catastrophic intraoperative hemorrhage.

Question 95

A 28-year-old man with Hereditary Multiple Exostoses (HME) reports a rapidly enlarging, painful mass on his posterior thigh. MRI reveals a sessile osteochondroma with a newly thickened cartilage cap measuring 3.5 cm. Which of the following histological features most strongly suggests malignant transformation to secondary chondrosarcoma?

Explanation

Secondary chondrosarcoma arising from an osteochondroma presents with a cartilage cap >2 cm in adults. Histologically, it is distinguished from benign cartilage by increased cellularity, pleomorphism, binucleation, and myxoid matrix changes.

Question 96

A 19-year-old male presents with a hard, painless mass on his proximal humerus. Radiographs are shown:

Imaging confirms a surface lesion causing saucerization of the underlying cortex with a sclerotic rim, but no medullary extension. Biopsy shows mature hyaline cartilage without atypia. What is the most likely diagnosis?

Explanation

Periosteal chondroma typically presents in young adults as a benign cartilaginous surface lesion that erodes the underlying cortex, creating a 'saucerized' defect bordered by sclerotic bone.

Question 97

A 65-year-old man sustains a pathologic fracture of the proximal humerus. Imaging shows a heavily calcified medullary lesion bordered by a highly aggressive, purely radiolucent area destroying the cortex. Histology reveals low-grade hyaline cartilage sharply juxtaposed next to a high-grade, non-cartilaginous spindle cell sarcoma. What is the diagnosis?

Explanation

Dedifferentiated chondrosarcoma is characterized by a classic 'biphasic' histologic pattern where a low-grade cartilaginous tumor abruptly transitions into a high-grade spindle cell sarcoma. This portends a very poor prognosis.

Question 98

A 24-year-old female presents with a destructive rib lesion. Biopsy reveals a highly cellular tumor composed of sheets of primitive, undifferentiated small round blue cells interspersed with distinct islands of well-differentiated, benign-appearing hyaline cartilage. What is the most likely diagnosis?

Explanation

Mesenchymal chondrosarcoma is a rare, aggressive tumor that often affects the jaws, ribs, and extraosseous tissues. Its hallmark is a biphasic histology consisting of small round blue cells and islands of mature hyaline cartilage.

Question 99

A 45-year-old male has deep thigh pain at night. Imaging shows a 6 cm cartilaginous lesion in the femoral diaphysis with focal endosteal scalloping involving 75% of the cortex. Core biopsy returns 'Atypical Cartilaginous Tumor / Grade 1 Chondrosarcoma'. What is the most appropriate joint-preserving surgical approach for this lesion?

Explanation

Recent guidelines support treating appendicular Atypical Cartilaginous Tumors (Grade 1 chondrosarcoma) with extended intralesional curettage, high-speed burring, and adjuvants (e.g., phenol, cryotherapy) to preserve function while maintaining low recurrence rates.

Question 100

A 12-year-old boy is diagnosed with Ewing sarcoma of the left ilium. During the initial staging workup, which of the following represents the single most significant prognostic factor for his overall survival?

Explanation

While pelvic location and large tumor volume are poor prognostic indicators, the presence of distant metastasis (primarily lung and bone marrow) at the time of diagnosis is the single most critical factor determining overall survival in Ewing sarcoma.

Orthopaedic Surgery Board Exam Review: ABOS Part I & AAOS OITE Prep Questions | Part 22210

ABOS Orthopedic Board Review: Bone Neoplasms, Chondromas, & Sarcoma Metastasis | Part 9

Key Takeaway

ABOS Orthopedic Board Review: Bone Neoplasms, Chondromas, & Sarcoma Metastasis | Part 9

Chapter Index