ABOS Board Review: Primary Bone Tumors & MSK Pathology

Question 1

A 35-year-old asymptomatic woman undergoes radiographs after a minor knee contusion. Imaging reveals a well-defined intramedullary lesion with "popcorn" calcifications in the distal femur.

What is the most appropriate next step in management?

Explanation

Asymptomatic enchondromas with classic radiographic features do not require biopsy or intervention. Observation with serial radiographs is appropriate management.

Question 2

Which of the following MRI findings is most indicative of a low-grade chondrosarcoma rather than an enchondroma in a long bone?

Explanation

Endosteal scalloping of more than two-thirds of the cortical thickness, cortical breakthrough, and a soft-tissue mass are strongly suggestive of chondrosarcoma. Enchondromas rarely cause deep endosteal scalloping in long bones.

Question 3

A 20-year-old male presents with a painless mass over his proximal humerus. Imaging shows a surface lesion < 3 cm with a "saucerized" appearance of the underlying cortex and an intact sclerotic margin.

What is the diagnosis?

Explanation

Periosteal chondromas are benign surface lesions typically presenting with saucerization of the underlying cortex and sclerotic margins. They must be differentiated from periosteal chondrosarcomas, which are usually larger and lack the sclerotic rim.

Question 4

A 28-year-old man presents with a pathologic fracture of the proximal phalanx of the ring finger after jamming his hand. Radiographs reveal an expansile, lucent lesion.

What is the most appropriate definitive management?

Explanation

For enchondromas of the hand presenting with a pathologic fracture, initial treatment is allowing the fracture to heal. Definitive management with intralesional curettage and bone grafting is performed subsequently.

Question 5

A 15-year-old boy presents with multiple enchondromas and multiple dark blue, compressible soft tissue nodules on his extremities. He is at highest risk for developing which of the following?

Explanation

Maffucci syndrome involves multiple enchondromas and soft-tissue hemangiomas. These patients have a nearly 100% lifetime risk of malignant transformation, most commonly to chondrosarcoma, as well as visceral malignancies.

Question 6

A 45-year-old male with a known distal femur osteochondroma reports recent onset of pain and growth of the mass. An MRI is obtained. Which cartilage cap thickness is considered the threshold most concerning for malignant transformation in an adult?

Explanation

In adults, a cartilage cap thicker than 1.5 to 2.0 cm (15-20 mm) on MRI is highly suspicious for malignant transformation of an osteochondroma to a secondary chondrosarcoma. Growth or new pain in adulthood also warrants immediate investigation.

Question 7

A 16-year-old boy presents with knee pain. Radiographs reveal a lucent lesion in the epiphysis of the proximal tibia with a thin sclerotic rim. Histology shows polygonal cells with grooved nuclei and "chicken-wire" calcifications. What is the diagnosis?

Explanation

Chondroblastoma is a rare, benign epiphyseal tumor seen in skeletally immature patients. The classic histologic finding is "chicken-wire" pericellular calcification surrounding chondroblasts.

Question 8

A 40-year-old man presents with chronic hip pain. Imaging demonstrates a lytic lesion in the femoral head epiphysis. Biopsy reveals malignant chondrocytes with abundant clear cytoplasm. This lesion is frequently misdiagnosed clinically and radiographically as which of the following?

Explanation

Clear cell chondrosarcoma typically arises in the epiphysis of long bones in adults (30-50 years). Because of its epiphyseal location, it is most often radiographically misdiagnosed as a chondroblastoma, which typically occurs in younger patients.

Question 9

A 65-year-old woman with a known low-grade chondrosarcoma presents with sudden, rapid enlargement of the lesion. Biopsy reveals a bimorphic pattern: a low-grade cartilage tumor adjacent to a high-grade non-cartilaginous sarcoma. What is the expected prognosis?

Explanation

Dedifferentiated chondrosarcoma presents with a classic bimorphic histological appearance. It is highly aggressive and carries a very poor prognosis, with a 5-year survival rate of 10-20%.

Question 10

A biopsy of a bone tumor reveals a biphasic pattern consisting of islands of well-differentiated hyaline cartilage interspersed with highly cellular areas of small, round blue cells in a hemangiopericytoma-like vascular pattern. What is the diagnosis?

Explanation

Mesenchymal chondrosarcoma is uniquely characterized by its biphasic histology: islands of benign-appearing cartilage mixed with primitive small round blue cells and a hemangiopericytomatous vascular pattern. It often occurs in the jaw or spine.

Question 11

Mutations in the isocitrate dehydrogenase 1 and 2 (IDH1/IDH2) genes are pathognomonic and most frequently associated with which of the following skeletal conditions?

Explanation

IDH1 and IDH2 somatic mutations are heavily implicated in the pathogenesis of Ollier disease, Maffucci syndrome, and solitary enchondromas. They result in abnormal chondrocyte proliferation through oncometabolite accumulation.

Question 12

A 25-year-old male presents with a painful, eccentric, metaphyseal radiolucent lesion in the proximal tibia. Histology shows lobules of myxoid and chondroid tissue separated by fibrous septa containing multinucleated giant cells. What is the recommended treatment?

Explanation

Chondromyxoid fibroma (CMF) is a benign but locally aggressive cartilage tumor. Treatment involves intralesional curettage; adding a local adjuvant (high-speed burr, phenol) decreases the relatively high recurrence rate.

Question 13

A 12-year-old girl is evaluated for multiple bony protuberances around her knees and ankles, leading to forearm bowing and short stature. The underlying genetic mutation for this condition primarily affects the synthesis of which of the following?

Explanation

Multiple Hereditary Exostoses (MHE) is caused by mutations in the EXT1 or EXT2 genes. These genes encode glycosyltransferases necessary for the proper synthesis of heparan sulfate proteoglycans.

Question 14

A 55-year-old male is diagnosed with a grade 2 conventional chondrosarcoma of the proximal femur. There is no evidence of metastasis. What is the mainstay of treatment?

Explanation

Conventional chondrosarcomas are largely resistant to both chemotherapy and radiation. The mainstay of treatment for intermediate to high-grade lesions is wide surgical resection with negative margins.

Question 15

A 32-year-old female presents with an incidental finding on a hand radiograph obtained after mild trauma. She has no pain at rest or night pain. Radiographs reveal a centrally located, lytic lesion in the proximal phalanx with stippled calcifications and no cortical breakthrough. What is the most appropriate next step in management?

Explanation

This is a classic asymptomatic enchondroma of the hand. Observation with serial radiographs is the standard of care for asymptomatic, non-destructive enchondromas without signs of malignant transformation.

Question 16

A 25-year-old male presents with a painless lump on his proximal humerus. Radiographs demonstrate a surface lesion causing saucerization of the underlying cortex with a well-defined sclerotic margin and no medullary involvement.

What is the most likely diagnosis?

Explanation

Periosteal chondromas are benign, slow-growing cartilage tumors on the bone surface. Radiographically, they characteristically cause saucerization of the underlying cortex with a thick sclerotic margin.

Question 17

Which of the following imaging features is the most reliable indicator for differentiating a low-grade (Grade 1) chondrosarcoma from a benign enchondroma in a long bone?

Explanation

Endosteal scalloping that involves more than 2/3 of the cortical thickness, along with cortical thickening and deep bone pain, highly suggests a low-grade chondrosarcoma over an enchondroma.

Question 18

Patients with Ollier disease and Maffucci syndrome frequently possess somatic mosaic mutations in which of the following genes?

Explanation

Enchondromatosis syndromes (Ollier disease and Maffucci syndrome) are driven by somatic mosaic point mutations in the IDH1 or IDH2 genes. EXT mutations are seen in multiple hereditary exostoses.

Question 19

A 32-year-old woman presents with a pathologic fracture of her proximal phalanx through a previously asymptomatic lytic lesion with stippled calcifications. What is the most appropriate initial management?

Explanation

Pathologic fractures through enchondromas in the hand should initially be allowed to heal with conservative immobilization. Curettage and bone grafting are performed electively once the fracture has healed.

Question 20

A 22-year-old male presents with knee pain. Radiographs reveal an eccentric, heavily scalloped lytic lesion in the proximal tibial metaphysis with a sclerotic rim. Histology shows lobules of myxoid and chondroid tissue with stellate cells and hypercellular peripheries. What is the diagnosis?

Explanation

Chondromyxoid fibroma is a rare benign cartilage tumor presenting as an eccentric metaphyseal lesion. Its histology classically shows lobulated areas of stellate or spindle cells in a myxoid background with hypercellular margins.

Question 21

A 14-year-old boy presents with chronic right knee pain. Radiographs show a well-circumscribed lytic lesion in the distal femoral epiphysis. Histological examination reveals mononuclear cells with longitudinal nuclear grooves and areas of "chicken-wire" calcification. What is the most likely diagnosis?

Explanation

Chondroblastoma is a benign cartilaginous tumor characteristically found in the epiphysis of skeletally immature patients. Histology typically reveals chondroblasts with grooved nuclei and pericellular "chicken-wire" calcification.

Question 22

In a skeletally mature patient with a solitary osteochondroma, malignant transformation to secondary chondrosarcoma is best indicated on MRI by a cartilage cap thickness greater than:

Explanation

A cartilage cap thickness greater than 2.0 cm in a skeletally mature adult is highly suspicious for malignant transformation to a secondary chondrosarcoma. Growth of the lesion after skeletal maturity is also a strong clinical indicator.

Question 23

Which of the following is the histological hallmark of a dedifferentiated chondrosarcoma?

Explanation

Dedifferentiated chondrosarcoma is characterized by a bimorphic histological pattern featuring a well-differentiated (low-grade) cartilaginous component lying adjacent to a high-grade, non-cartilaginous sarcoma, with an abrupt transition between the two.

Question 24

A 35-year-old male is noted to have an asymptomatic, 1.5 cm well-circumscribed lesion in the proximal phalanx with stippled calcifications found incidentally on X-ray for a sprained finger.

What is the most appropriate management?

Explanation

Asymptomatic enchondromas discovered incidentally require only observation and serial radiographs to confirm stability. Surgical intervention is reserved for symptomatic lesions, enlarging lesions, or impending pathologic fractures.

Question 25

Mutations in the EXT1 and EXT2 genes, seen in multiple hereditary exostoses (MHE), lead to the impaired synthesis of which of the following?

Explanation

EXT1 and EXT2 gene mutations affect the EXT-polymerase complex, leading to impaired synthesis of heparan sulfate. This disruption alters normal Indian hedgehog (Ihh) signaling at the growth plate, leading to osteochondroma formation.

Question 26

What is the recommended surgical management for a biopsy-proven atypical cartilaginous tumor (Grade 1 chondrosarcoma) contained entirely within the medullary canal of the distal femur?

Explanation

Atypical cartilaginous tumors (Grade 1 chondrosarcomas) in the long bones of the appendicular skeleton are safely and effectively treated with extensive intralesional curettage and local adjuvants. Wide resection is reserved for higher grade tumors or pelvic lesions.

Question 27

A 55-year-old male presents with deep pelvic pain. Radiographs show a large destructive mass in the ilium with "popcorn" calcifications. Core biopsy confirms Grade II chondrosarcoma. What is the most appropriate treatment?

Explanation

Intermediate to high-grade chondrosarcomas (Grades II and III), as well as any grade of chondrosarcoma in the pelvis, are treated with wide surgical resection. Chondrosarcomas are generally resistant to both standard chemotherapy and radiation.

Question 28

A 28-year-old female presents with multiple hard, bony swellings in her hands and several bluish soft-tissue nodules on her forearm that contain phleboliths on X-ray. What is her most likely diagnosis?

Explanation

Maffucci syndrome is characterized by the presence of multiple enchondromas associated with soft-tissue venous malformations (hemangiomas), which frequently contain calcified phleboliths. It carries a high risk of malignant transformation.

Question 29

A 17-year-old boy presents with a firm mass on the surface of his proximal tibia. Imaging demonstrates a subperiosteal lesion causing saucerization of the outer cortex, bordered by solid reactive sclerosis.

There is no marrow invasion. What is the most likely diagnosis?

Explanation

Periosteal chondromas develop under the periosteum, characteristically eroding the underlying cortex (saucerization) while inducing a dense sclerotic margin. They lack the perpendicular "hair-on-end" periosteal reaction seen in periosteal osteosarcoma.

Question 30

Which of the following distinct histological patterns is characteristic of mesenchymal chondrosarcoma?

Explanation

Mesenchymal chondrosarcoma is defined by a bimorphic histology featuring undifferentiated small blue round cells surrounding discrete islands of relatively well-differentiated benign-appearing hyaline cartilage.

Question 31

The IDH1 and IDH2 mutations commonly found in central chondrosarcomas and enchondromatosis syndromes promote tumorigenesis by producing which of the following oncometabolites?

Explanation

Mutant IDH1/2 enzymes gain a neomorphic activity that converts alpha-ketoglutarate into the oncometabolite D-2-hydroxyglutarate (D-2-HG). This leads to DNA hypermethylation and altered cellular differentiation.

Question 32

A 45-year-old male presents with hip pain. Radiographs reveal a lytic lesion in the proximal femoral epiphysis. Biopsy reveals cells with distinct borders, clear cytoplasm, and central round nuclei in a background of cartilaginous matrix with scattered giant cells. Diagnosis?

Explanation

Clear cell chondrosarcoma typically occurs in the epiphyses of adults (resembling chondroblastoma radiographically, but in an older age group). Histologically, it displays large cells with clear cytoplasm and distinct boundaries alongside a cartilaginous matrix.

Question 33

Patients with Multiple Hereditary Exostoses (MHE) have an increased lifetime risk of malignant transformation compared to the general population. What is the approximate rate of malignant transformation in MHE?

Explanation

While solitary osteochondromas have a malignant transformation risk of <1%, patients with Multiple Hereditary Exostoses (MHE) have a higher lifetime risk, typically estimated between 1% and 5%.

Question 34

A 65-year-old male with a known history of Ollier disease presents with a rapidly enlarging, painful mass in his left hand over the past 3 months.

Given the sudden clinical change, what is the most likely complication?

Explanation

Patients with Ollier disease have a high risk (up to 25-30%) of malignant transformation of their enchondromas. Rapid growth or new pain in a previously stable lesion strongly suggests secondary chondrosarcoma.

Question 35

When evaluating a cartilaginous lesion of the medullary canal, which of the following histological findings strongly favors a diagnosis of low-grade chondrosarcoma over an enchondroma?

Explanation

The permeation and entrapment of pre-existing host bone trabeculae by cartilaginous tissue is a hallmark of invasion, which strongly differentiates a low-grade chondrosarcoma from a benign enchondroma.

Question 36

A 35-year-old asymptomatic male incidentally discovers a 3 cm medullary lesion with stippled "rings and arcs" calcification in the proximal humerus.

What is the most appropriate next step in management?

Explanation

This is a classic presentation of an asymptomatic enchondroma, characterized by central "rings and arcs" calcifications without cortical destruction. Observation with serial radiographs is the standard of care for asymptomatic incidental enchondromas in the appendicular skeleton.

Question 37

A 28-year-old male presents with a painless palpable mass over the proximal humerus. Radiographs show a small surface lesion causing cortical saucerization with a well-defined sclerotic margin.

What is the most likely diagnosis?

Explanation

Periosteal chondromas are benign surface lesions typically presenting with cortical saucerization and a thick sclerotic margin. Unlike periosteal chondrosarcomas, they are usually less than 3 cm in size and possess a well-defined, intact sclerotic rim.

Question 38

A 12-year-old boy with multiple enchondromatosis presents with a rapid increase in the size of a thigh lesion. He is also noted to have multiple soft tissue hemangiomas. Which genetic mutation is most strongly associated with this specific syndrome?

Explanation

The patient has Maffucci syndrome, distinguished from Ollier disease by the presence of soft tissue hemangiomas. Both Ollier disease and Maffucci syndrome are strongly associated with somatic mutations in the IDH1 or IDH2 genes.

Question 39

A 15-year-old boy presents with knee pain. Radiographs reveal a 2 cm eccentric, purely lytic lesion in the epiphysis of the distal femur. Histology demonstrates mononuclear cells with grooved nuclei and "chicken-wire" calcifications. What is the most common complication following the standard surgical treatment of this lesion?

Explanation

The diagnosis is chondroblastoma, typically treated with extended intralesional curettage and bone grafting. Despite standard treatment, local recurrence is the most common complication, occurring in up to 15-20% of cases.

Question 40

A 22-year-old female presents with a moderately painful, eccentric, radiolucent lesion in the metaphysis of the proximal tibia. Histology reveals a lobular architecture with hypercellular peripheries and hypocellular centers containing stellate cells in a myxoid background. What is the most appropriate treatment?

Explanation

The diagnosis is chondromyxoid fibroma (CMF), a benign but locally aggressive cartilage tumor. Treatment requires extended intralesional curettage with a high-speed burr and local adjuvants (like phenol or cryotherapy) to minimize the risk of local recurrence.

Question 41

A 48-year-old male with a known history of an osteochondroma on his distal femur notices recent enlargement and increasing pain. MRI demonstrates a cartilaginous cap thickness of 2.5 cm. What is the most likely diagnosis?

Explanation

In skeletally mature adults, an enlarging osteochondroma with pain and a cartilage cap thicker than 2 cm is highly suspicious for malignant transformation into a secondary chondrosarcoma. Wide surgical resection is indicated.

Question 42

A 30-year-old female sustains a closed, non-displaced fracture of her proximal phalanx after minor trauma. Radiographs reveal an underlying expansile, well-circumscribed radiolucent lesion with stippled calcifications.

What is the most appropriate management?

Explanation

This is a pathologic fracture through an enchondroma of the hand. The standard of care is to allow the fracture to heal with immobilization first, then perform intralesional curettage and bone grafting to prevent recurrence.

Question 43

A 35-year-old presents with a painless, swollen ring finger. Radiographs show a centrally located, lytic lesion in the proximal phalanx with stippled calcifications.

What is the most appropriate initial management?

Explanation

This is a classic presentation of an asymptomatic enchondroma in the hand. Asymptomatic, incidentally found enchondromas should be observed; surgical intervention is reserved for symptomatic lesions or pathologic fractures.

Question 44

A 12-year-old boy presents with right knee pain. Radiographs reveal an eccentric, lytic surface lesion causing cortical scalloping on the proximal medial tibia without medullary extension.

What is the most likely diagnosis?

Explanation

Periosteal (juxtacortical) chondromas typically present as eccentric, surface lesions causing a well-defined cortical scalloping with sclerotic margins. They usually measure less than 3 cm and do not invade the medullary canal.

Question 45

A 45-year-old woman is evaluated for a new painful mass in her proximal humerus. She has a known history of Ollier disease. Radiographs show a destructive lesion arising from a pre-existing calcified intramedullary tumor. Which of the following genetic mutations is most strongly associated with her underlying syndrome?

Explanation

Ollier disease (multiple enchromatosis) and Maffucci syndrome are strongly associated with somatic mutations in the IDH1 or IDH2 genes. EXT1 mutations are associated with hereditary multiple exostoses.

Question 46

A 25-year-old male presents with chronic knee pain. Imaging reveals an epiphyseal lytic lesion in the distal femur. Histology demonstrates mononuclear cells with longitudinal nuclear grooves and areas of eosinophilic matrix with "chicken-wire" calcifications. What is the diagnosis?

Explanation

Chondroblastomas are benign, cartilage-producing tumors that characteristically occur in the epiphysis of long bones in young patients. Histology classically shows chondroblasts with grooved nuclei and "chicken-wire" pericellular calcifications.

Question 47

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

Explanation

Endosteal scalloping that exceeds two-thirds of the cortical thickness, cortical breakthrough, and soft tissue mass are hallmark signs differentiating a low-grade chondrosarcoma from an enchondroma. Enchondromas typically cause minimal or no endosteal scalloping in long bones.

Question 48

A 22-year-old patient presents with a palpable mass on the posterior surface of the proximal humerus.

A biopsy confirms a periosteal chondroma. What is the recommended treatment for a symptomatic periosteal chondroma?

Explanation

Symptomatic periosteal chondromas are best treated with marginal or en bloc excision, including the underlying sclerotic cortex, to minimize the risk of local recurrence. Intralesional curettage has a significantly higher recurrence rate.

Question 49

A 16-year-old male is diagnosed with an osteoid osteoma of the proximal femur. Which of the following best describes the molecular etiology of his severe nocturnal pain?

Explanation

The severe nocturnal pain characteristic of osteoid osteoma is caused by high levels of prostaglandins, particularly PGE2, produced by the nidus. This is why the pain is classically and dramatically relieved by NSAIDs.

Question 50

A 14-year-old girl complains of increasing right thigh pain. Radiographs demonstrate a diaphyseal permeative lytic lesion with an "onion skin" periosteal reaction. A biopsy is planned. Which cytogenetic abnormality is most likely to be found?

Explanation

The patient's presentation is classic for Ewing sarcoma. Ewing sarcoma is primarily driven by a balanced translocation between chromosomes 11 and 22, t(11;22)(q24;q12), which results in the EWS-FLI1 fusion protein.

Question 51

A patient with suspected Maffucci syndrome presents with a rapidly growing hand mass.

Besides a high risk for malignant transformation to chondrosarcoma, patients with Maffucci syndrome are at a significantly increased risk for which of the following?

Explanation

Maffucci syndrome (multiple enchondromas and soft tissue hemangiomas) carries a very high risk of malignant transformation. This includes not only chondrosarcoma but also visceral, brain (e.g., astrocytomas), and ovarian malignancies.

Question 52

A 30-year-old woman presents with knee pain. Radiographs show an eccentric, lytic epiphyseal lesion extending to the subchondral bone in the proximal tibia. A biopsy demonstrates multinucleated giant cells in a background of uniform mononuclear cells. What is the molecular target of the pharmacological agent used for unresectable cases of this tumor?

Explanation

The diagnosis is a Giant Cell Tumor (GCT) of bone. Denosumab, a monoclonal antibody that targets RANK Ligand (RANKL), is used for unresectable or metastatic GCTs to inhibit the formation and function of osteoclast-like giant cells.

Question 53

A 9-year-old boy presents with a pathologic fracture of the proximal humerus after a minor fall. Radiographs reveal a central, lytic, well-circumscribed diaphyseal-metaphyseal lesion with a "fallen leaf" sign. Which of the following is true regarding this condition?

Explanation

This describes a unicameral (simple) bone cyst (UBC). As the child grows, a "latent" UBC will migrate away from the physis into the diaphysis, whereas an "active" cyst remains adjacent to the physis.

Question 54

A 24-year-old male presents with multiple asymmetric nodular deformities of the hands and feet, along with multiple dark-blue soft tissue masses. Genetic testing would most likely reveal a somatic mutation in which of the following genes?

Explanation

This patient has Maffucci syndrome, characterized by multiple enchondromas and soft-tissue hemangiomas. It is caused by somatic mutations in the IDH1 or IDH2 genes.

Question 55

A 30-year-old female presents with a closed, minimally displaced pathologic fracture of the proximal phalanx of the index finger. Radiographs show an expansile, centrally located lytic lesion with stippled calcifications.

What is the most appropriate initial management?

Explanation

Enchondromas are the most common primary bone tumor of the hand. When presenting with a pathologic fracture, the initial treatment is immobilization to allow fracture healing, followed by elective curettage and bone grafting.

Question 56

Which of the following histologic features is the most reliable discriminator for diagnosing a low-grade chondrosarcoma rather than a benign enchondroma?

Explanation

Trapping of host lamellar bone and permeation into surrounding marrow spaces or Haversian canals are hallmarks of malignancy (chondrosarcoma). Enchondromas grow in a lobular pattern but respect surrounding host bone without permeative infiltration.

Question 57

A 15-year-old boy presents with a painless mass over the proximal humerus. Radiographs show a small (< 3 cm), cortically based lucent lesion with a sclerotic margin and cortical saucerization.

What is the most likely diagnosis?

Explanation

Periosteal chondromas typically present in the second decade as small (< 3 cm) surface lesions with cortical saucerization and a sclerotic inner margin. Periosteal chondrosarcomas have a similar appearance but are generally larger (> 3 cm) and occur in older adults.

Question 58

Which of the following is an accurate characteristic regarding the inheritance and genetic profile of Ollier disease?

Explanation

Ollier disease (multiple enchondromatosis) is a non-hereditary, sporadic disorder. It is caused by post-zygotic somatic mosaic mutations in the IDH1 or IDH2 genes.

Question 59

A 45-year-old man with a known asymptomatic distal femur enchondroma presents with new-onset, progressive night pain over the past 3 months. Imaging shows increased radiolucency and endosteal scalloping > 2/3 of the cortical thickness. Biopsy confirms secondary chondrosarcoma. What is the most appropriate definitive treatment?

Explanation

Chondrosarcomas are generally insensitive to chemotherapy and radiation. The standard treatment for conventional chondrosarcoma (grade 2 or higher) is wide surgical resection to achieve negative margins.

Question 60

In evaluating an intramedullary cartilaginous lesion of the distal femur, which MRI finding best distinguishes a bone infarct from an enchondroma?

Explanation

A bone infarct is classically characterized by a serpiginous rim of low signal on T1 and T2-weighted images (the double-line sign). Enchondromas typically show a lobulated, hyperintense pattern on T2-weighted images corresponding to their high water content.

Question 61

A 32-year-old woman is diagnosed with an atypical cartilaginous tumor (Grade 1 chondrosarcoma) of the proximal humerus. What is the currently recommended surgical management?

Explanation

Atypical cartilaginous tumors (Grade 1 chondrosarcomas) in the appendicular skeleton are increasingly treated with extended intralesional curettage and local adjuvants (e.g., high-speed burr, cryotherapy, or phenol). This provides excellent local control while preserving bone stock and joint function.

Question 62

A 22-year-old female presents with multiple hard bony protuberances and bluish soft-tissue nodules on her hands. Radiographs reveal multiple enchondromas. What is her lifetime risk of developing any malignancy?

Explanation

This patient has Maffucci syndrome, characterized by multiple enchondromas and soft-tissue hemangiomas. Patients with Maffucci syndrome have a lifetime risk of developing ANY malignancy (including chondrosarcoma and visceral/brain malignancies) approaching 100%, which is higher than the risk in Ollier disease.

Question 63

A 34-year-old male presents with acute pain in his ring finger after a minor jamming injury. Radiographs show a pathologic fracture through a central lytic lesion with stippled calcifications in the proximal phalanx.

What is the most appropriate management?

Explanation

Enchondromas are the most common primary bone tumors of the hand. When presenting with a pathologic fracture, the standard treatment is to immobilize the digit to allow the fracture to heal, followed later by curettage and bone grafting to prevent recurrence.

Question 64

A 60-year-old male presents with deep thigh pain. Imaging reveals a large distal femoral metaphyseal lesion. Biopsy demonstrates well-differentiated hyaline cartilage sharply demarcated from a high-grade pleomorphic spindle cell sarcoma. What is the diagnosis?

Explanation

Dedifferentiated chondrosarcoma is characterized by a bimorphic histologic appearance, where a low-grade chondrosarcoma lies adjacent to a high-grade non-cartilaginous sarcoma. This abrupt histological transition is a hallmark of the disease.

Question 65

A 35-year-old male presents with chronic hip pain. Radiographs demonstrate a lytic lesion with a sclerotic margin localized specifically to the proximal femoral epiphysis. Histological analysis shows cells with abundant clear cytoplasm and distinct cell membranes, mixed with areas of conventional chondrosarcoma. What is the most likely diagnosis?

Explanation

Clear cell chondrosarcoma is a rare, low-grade malignant cartilage tumor that typically occurs in the epiphysis of long bones in adults. Histologically, it features large cells with clear cytoplasm, which differentiates it from chondroblastoma.

Question 66

Which of the following histological features is the most reliable for distinguishing a low-grade conventional chondrosarcoma from a benign enchondroma?

Explanation

The most reliable histological feature to differentiate low-grade chondrosarcoma from an enchondroma is the permeation of tumor cells into the surrounding normal host trabecular bone. Enchondromas typically have well-defined margins and do not trap or permeate native bony trabeculae.

Question 67

A 12-year-old boy presents with multiple cartilaginous lesions predominantly affecting the right side of his body, causing limb-length discrepancy. Genetic testing of the lesional tissue is most likely to reveal a somatic mutation in which of the following genes?

Explanation

The patient has Ollier disease, characterized by multiple enchondromas with a unilateral predominance. Both solitary enchondromas and enchondromatosis syndromes (Ollier and Maffucci) are strongly associated with somatic mutations in the IDH1 or IDH2 genes.

Question 68

A 25-year-old male presents with multiple enchondromas predominantly affecting the right hand and leg, along with multiple soft-tissue venous malformations. What genetic mutation is most strongly associated with this condition, and what is the approximate risk of malignant transformation of the bone lesions?

Explanation

Maffucci syndrome is characterized by multiple enchondromas and soft-tissue hemangiomas, and is linked to somatic IDH1 or IDH2 mutations. Patients have a high risk of malignant transformation to chondrosarcoma (approximately 30-40%), as well as an increased risk of visceral malignancies.

Question 69

A 30-year-old right-hand-dominant carpenter presents with acute pain in his right ring finger after a minor twisting injury. Radiographs show a well-circumscribed, lucent lesion in the proximal phalanx with a pathologic fracture.

What is the most appropriate initial management for this patient?

Explanation

The patient has a pathologic fracture through an enchondroma of the hand. The standard standard of care is to allow the fracture to heal with immobilization first, followed by elective curettage and bone grafting to prevent recurrence.

Question 70

A 15-year-old male presents with a painless mass on the proximal humerus. Radiographs demonstrate a 2.5 cm surface lesion with underlying cortical saucerization and a sclerotic rim.

Biopsy is performed. Which of the following histologic features is characteristic of this lesion and must not be overinterpreted as malignancy?

Explanation

Periosteal (juxtacortical) chondromas often exhibit high cellularity, mild pleomorphism, and binucleate cells. In a small surface lesion (<3 cm) with an intact sclerotic cortex, these features represent a benign periosteal chondroma and should not be mistaken for low-grade chondrosarcoma.

Question 71

A 14-year-old boy presents with progressive knee pain. Radiographs reveal a 2 cm eccentric, purely lytic lesion in the distal femoral epiphysis with a thin sclerotic margin. MRI shows extensive surrounding bone marrow edema. What is the most likely histologic finding upon biopsy of this lesion?

Explanation

The clinical presentation is classic for a chondroblastoma, an epiphyseal lesion occurring in skeletally immature patients. Histology characteristically shows uniform polyhedral mononuclear cells (chondroblasts) and distinct pericellular "chicken-wire" calcifications.

Question 72

A 22-year-old woman presents with chronic, dull pain in her proximal leg. Radiographs reveal an eccentric, heavily scalloped, lytic metaphyseal lesion in the proximal tibia with a distinct sclerotic rim. There is no matrix calcification. What is the most appropriate definitive treatment for this condition?

Explanation

Chondromyxoid fibroma (CMF) is a rare benign cartilage tumor presenting as an eccentric, scalloped metaphyseal lesion. The standard of care is extended intralesional curettage with adjuvant treatment (e.g., high-speed burr) and bone grafting due to a high local recurrence risk with simple curettage alone.

Question 73

A 35-year-old man presents with a hard mass on the distal femur. Imaging shows a 6 cm lobulated surface mass with dense ring-and-arc calcifications. The lesion is elevating the periosteum but the underlying cortex is intact without medullary involvement.

What radiographic feature most strongly differentiates this from a periosteal chondroma?

Explanation

Periosteal chondromas and periosteal chondrosarcomas both occur on the bone surface with an intact cortex and absent medullary involvement. A primary differentiating factor is size; lesions greater than 3 cm are highly suspicious for periosteal chondrosarcoma.

Question 74

A 40-year-old patient undergoes an MRI for a suspected meniscal tear. An incidental intramedullary lesion is found in the distal femur. It demonstrates a serpentine, well-demarcated border with a low-signal rim on both T1 and T2 sequences. How is this lesion radiographically distinct from an enchondroma?

Explanation

The MRI description of a serpentine border with a low-signal rim is classic for a bone infarct. In contrast, enchondromas typically present as lobulated hyperintense lesions on T2 MRI with stippled, "popcorn" or rings-and-arcs matrix calcifications on radiographs.

Question 75

A 32-year-old right-hand-dominant male presents with sudden pain in his right ring finger after a mild twisting injury. Radiographs demonstrate a pathologic fracture through a centrally located, lytic, expansile lesion with stippled calcifications in the proximal phalanx. What is the most appropriate management strategy?

Explanation

Enchondromas are the most common primary bone tumors of the hand. When complicated by a pathologic fracture, the standard management is immobilization to allow fracture healing, followed by elective intralesional curettage and grafting to prevent recurrence.

Question 76

Which of the following genetic mutations is primarily responsible for the development of multiple enchondromatosis (Ollier disease)?

Explanation

Ollier disease is characterized by multiple enchondromas and is associated with somatic mosaic mutations in the IDH1 and IDH2 genes. EXT1 and EXT2 mutations are associated with multiple hereditary exostoses.

Question 77

A 55-year-old male presents with worsening thigh pain. Biopsy of a proximal femur lesion reveals a bimorphic histological pattern showing a low-grade hyaline cartilage tumor abruptly juxtaposed with a high-grade spindle cell sarcoma. Which of the following is the most likely diagnosis?

Explanation

Dedifferentiated chondrosarcoma classically presents with a low-grade cartilage tumor adjacent to a highly malignant, non-cartilaginous spindle cell sarcoma. This abrupt transition is the histological hallmark and portends a very poor prognosis.

Question 78

A 22-year-old male presents with a slow-growing, painless mass on his proximal humerus.

Imaging reveals a 2.5 cm surface lesion causing saucerization of the underlying cortex with a sclerotic margin. What is the definitive treatment to minimize local recurrence?

Explanation

The clinical and radiographic presentation is classic for a periosteal chondroma. To minimize recurrence, treatment requires marginal excision that includes the underlying sclerotic cortex.

Question 79

A 45-year-old male presents with chronic, mild hip pain. Radiographs reveal a lytic lesion in the epiphysis of the proximal femur. Histological examination shows large cells with distinct borders, abundant clear cytoplasm, and interspersed woven bone. What is the diagnosis?

Explanation

Clear cell chondrosarcoma is a low-grade malignant tumor that classically occurs in the epiphysis of long bones in adults (30-50 years). Although chondroblastoma is also epiphyseal, it typically occurs in skeletally immature patients and lacks the abundant clear cytoplasm seen here.

Question 80

A 16-year-old male undergoes curettage and bone grafting for an epiphyseal lesion in the proximal humerus. Histopathology reveals mononuclear cells with clefted, "coffee-bean" nuclei and areas of fine, pericellular "chicken-wire" calcification. Despite its benign nature, what complication must be monitored for?

Explanation

The histology describes a chondroblastoma. Though considered benign, chondroblastomas have a recognized potential (1-2%) to metastasize to the lungs.

Question 81

A 24-year-old female presents with a painless, eccentric, expansile metaphyseal lesion in her proximal tibia. Histopathology demonstrates a lobular architecture with stellate and spindle cells embedded in a myxoid background, with multinucleated giant cells clustered at the lobular peripheries. What is the most likely diagnosis?

Explanation

Chondromyxoid fibroma typically presents as an eccentric metaphyseal lesion in young adults. Its classic histology features lobules of myxoid tissue containing stellate cells, with giant cells localized at the periphery of these lobules.

Question 82

A 60-year-old female undergoes an MRI of her knee for a suspected meniscal tear. An incidental intramedullary distal femur lesion is identified. Which of the following MRI findings best distinguishes a bone infarct from an enchondroma?

Explanation

Bone infarcts are distinguished on MRI by a serpiginous, well-defined border frequently demonstrating the 'double-line' sign (hyperintense inner ring, hypointense outer ring on T2). Enchondromas typically show characteristic lobulated T2 hyperintensity.

Question 83

A 30-year-old male presents with a destructive lesion in the mandible. Biopsy reveals a bimorphic pattern consisting of islands of well-differentiated hyaline cartilage surrounded by sheets of highly cellular, undifferentiated small round blue cells with hemangiopericytoma-like vessels. What is the diagnosis?

Explanation

Mesenchymal chondrosarcoma is an aggressive tumor often found in the jaw, spine, or ribs. Its hallmark is a bimorphic histological appearance featuring cartilage islands intermixed with small round blue cells and staghorn vasculature.

Question 84

A 14-year-old boy with multiple hemangiomas and venous malformations is found to have multiple asymmetric cartilaginous lesions in his hands and long bones. He is diagnosed with Maffucci syndrome. Compared to Ollier disease, he is at an inherently higher risk for which of the following?

Explanation

Maffucci syndrome is characterized by multiple enchondromas and vascular malformations. In addition to a near 100% risk of chondrosarcoma, these patients have a significantly higher risk of extraskeletal malignancies, notably astrocytomas and GI tract carcinomas, compared to Ollier disease.

Question 85

In evaluating an intramedullary cartilaginous lesion of the proximal humerus, which of the following clinical or radiographic features is the most reliable indicator of malignant transformation to a chondrosarcoma?

Explanation

In the absence of a fracture or other mechanical cause, new or unrelenting rest pain in a previously asymptomatic cartilaginous lesion is the most sensitive and reliable clinical indicator of malignant transformation to chondrosarcoma.

Question 86

An asymptomatic 45-year-old male has an incidental finding on a hand radiograph.

The image shows a well-circumscribed, central lucent lesion in the proximal phalanx with focal stippled calcifications. No cortical destruction is noted. What is the recommended management?

Explanation

The image demonstrates a classic benign enchondroma of the hand. For an asymptomatic, structurally sound enchondroma without concerning features, the standard of care is serial clinical and radiographic observation.

Question 87

A 50-year-old male with a known history of multiple hereditary exostoses (MHE) reports rapid growth of a previously stable osteochondroma on his pelvis. On MRI, what cartilage cap thickness threshold is most highly suspicious for secondary chondrosarcoma in an adult?

Explanation

In skeletally mature adults, a cartilage cap thickness greater than 2.0 cm on MRI or CT is highly suspicious for malignant transformation of an osteochondroma to a secondary chondrosarcoma.

Question 88

Which of the following inheritance patterns correctly describes the genetic transmission of multiple enchondromatosis (Ollier disease)?

Explanation

Ollier disease (multiple enchondromatosis) typically occurs sporadically due to post-zygotic somatic mosaic mutations in the IDH1 or IDH2 genes. It is not considered an inherited condition.

Question 89

Primary chondrosarcoma most frequently arises in which of the following anatomic locations, which also happens to present significant surgical challenges and carries a poorer prognosis?

Explanation

The pelvis is the most common anatomic site for primary chondrosarcoma. Because these tumors often grow quite large before detection and are difficult to resect with wide margins in the pelvis, they generally carry a poorer prognosis.

Question 90

A 50-year-old male is diagnosed with an Atypical Cartilaginous Tumor (Grade 1 Chondrosarcoma) confined within the medullary canal of the proximal femur, without cortical breakthrough. Which surgical treatment strategy is currently favored for this specific presentation?

Explanation

For central atypical cartilaginous tumors (Grade 1 chondrosarcomas) of the long bones without cortical destruction, extended intralesional curettage with high-speed burring and local adjuvants (e.g., phenol, cryotherapy) is increasingly favored over wide resection, demonstrating low recurrence rates and superior functional outcomes.

Question 91

Histological evaluation of a curettage specimen from a benign hand enchondroma is most likely to demonstrate which of the following?

Explanation

Benign enchondromas consist of lobules of mature hyaline cartilage. The chondrocytes reside in well-defined lacunae with small, single, uniform nuclei and lack significant atypia, hypercellularity, or prominent binucleation.

Question 92

A patient with a presumed cartilaginous bone tumor undergoes molecular testing, revealing an H3F3B (Histone H3.3) mutation. This finding is virtually pathognomonic for which of the following tumors?

Explanation

Mutations in the H3F3B gene are highly specific to chondroblastoma (found in up to 95% of cases). In contrast, H3F3A mutations are classically seen in giant cell tumors of bone.

Question 93

A 15-year-old male presents with a symptomatic surface lesion on his proximal humerus.

Imaging displays a 2 cm lesion causing saucerization of the outer cortex, with an intact sclerotic rim and without medullary extension. Which feature most reliably differentiates this lesion from a periosteal osteosarcoma?

Explanation

Periosteal chondromas typically cause a well-defined saucerization of the outer cortex with a thick sclerotic rim and do not invade the medullary canal. Periosteal osteosarcoma tends to be larger, lacks a well-defined sclerotic rim, and often exhibits aggressive periosteal reactions.

Question 94

A 25-year-old female presents with severe asymmetric limb deformity and multiple bluish subcutaneous nodules. Radiographs reveal multiple expansile cartilaginous lesions in the phalanges and long bones. Which of the following is true regarding this patient's condition compared to Ollier disease?

Explanation

The patient has Maffucci syndrome, characterized by multiple enchondromas and soft-tissue venous malformations (hemangiomas). Compared to Ollier disease, Maffucci syndrome carries a significantly higher risk of extraskeletal malignancies, including astrocytomas, GI tumors, and angiosarcomas.

Question 95

A 22-year-old male presents with a slow-growing, painless mass on his proximal humerus. Radiographs demonstrate the surface lesion shown below, measuring 2.5 cm with underlying cortical saucerization.

Biopsy reveals hypercellular cartilage with no cytological atypia or host bone permeation. What is the recommended definitive treatment?

Explanation

The image and clinical presentation describe a periosteal (juxtacortical) chondroma, a benign surface cartilage tumor. The treatment of choice for symptomatic lesions is marginal excision en bloc with the underlying sclerotic bone to minimize the risk of recurrence.

Question 96

A 30-year-old man presents with acute hand pain after a minor low-energy twisting injury. Radiographs show a pathologic fracture through a well-circumscribed, lucent lesion with central calcifications in the proximal phalanx, consistent with an enchondroma.

What is the most appropriate initial management for this pathologic fracture?

Explanation

Most pathologic fractures through a benign enchondroma in the hand should be managed by allowing the fracture to heal first with conservative care. Once healed, definitive intralesional curettage and bone grafting can be performed to restore structural integrity.

Question 97

A 45-year-old male complains of new-onset, deep aching pain in his right shoulder, primarily occurring at rest and at night. Radiographs demonstrate a 6 cm cartilaginous intramedullary lesion in the proximal humerus. Which of the following radiographic features most strongly differentiates a secondary low-grade chondrosarcoma from a benign enchondroma?

Explanation

While both enchondromas and low-grade chondrosarcomas share stippled calcifications, endosteal scalloping involving greater than 2/3 of the cortical thickness, cortical breakthrough, and the presence of rest pain strongly indicate malignant transformation to a chondrosarcoma.

Question 98

A 40-year-old male presents with chronic hip pain. Radiographs reveal a purely lytic, slightly expansile lesion in the femoral head epiphysis extending to the articular surface. Biopsy demonstrates cells with abundant clear cytoplasm, distinct cell membranes, and interspersed areas of hyaline cartilage. What is the most likely diagnosis?

Explanation

Clear cell chondrosarcoma is a low-grade malignant cartilage tumor that characteristically arises in the epiphysis of long bones in adults aged 30-50. It must be histologically and clinically distinguished from chondroblastoma, which typically occurs in pediatric patients with open physes.

Question 99

Somatic mosaic mutations in the IDH1 or IDH2 (isocitrate dehydrogenase) genes are most frequently associated with the pathogenesis of which of the following pairs of conditions?

Explanation

Mutations in the IDH1 and IDH2 genes are strongly linked to the development of central cartilaginous tumors. These somatic mutations are found in a majority of solitary enchondromas, as well as in patients with Ollier disease and Maffucci syndrome.

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

ABOS Orthopedic Board Review: Primary Bone Tumors, Chondromas, & MSK Pathology | Part 9

Key Takeaway

ABOS Orthopedic Board Review: Primary Bone Tumors, Chondromas, & MSK Pathology | Part 9

Chapter Index