Question 1

A 15-year-old male presents with chronic knee pain. Radiographs reveal a well-circumscribed, eccentrically located lytic lesion in the proximal tibial epiphysis with a thin sclerotic rim. Biopsy demonstrates mononuclear cells with longitudinal nuclear grooves and areas of pericellular 'chicken-wire' calcification. Which of the following is the most appropriate initial management?

Explanation

The clinical and histological findings are classic for chondroblastoma, a benign but locally aggressive epiphyseal tumor. The gold standard treatment is extended intralesional curettage with high-speed burring and bone grafting or cementation.

Question 2

A 45-year-old male undergoes a core needle biopsy of a deep thigh mass. Histology reveals a uniform population of round cells, a prominent myxoid stroma, and a branching capillary network resembling 'chicken-wire'. Which specific chromosomal translocation is most characteristic of this soft tissue sarcoma?

Explanation

Myxoid liposarcoma is characterized by the t(12;16)(q13;p11) translocation, which creates the FUS-DDIT3 fusion gene. The 'chicken-wire' capillary network and myxoid stroma are hallmark histological features.

Question 3

A 12-year-old female presents with a rapidly progressive left-sided thoracic scoliosis. Neurological examination reveals a loss of pain and temperature sensation in her bilateral upper extremities with preserved fine touch and proprioception. What is the most likely primary etiology of her spinal deformity?

Explanation

A left-sided thoracic curve and rapidly progressive scoliosis are 'atypical' features warranting an MRI. The cape-like loss of pain and temperature sensation is pathognomonic for syringomyelia, which is most commonly associated with a Chiari I malformation.

Question 4

A 60-year-old patient presents with a large, slow-growing retroperitoneal mass. Biopsy reveals mature adipocytes with focal areas of nuclear atypia and hyperchromatic stromal cells. Molecular testing demonstrates amplification of a specific gene on chromosome 12q13-15. Which of the following genes is amplified in this tumor?

Explanation

Well-differentiated liposarcoma (and atypical lipomatous tumors) are characterized by the amplification of MDM2 and CDK4 genes on chromosome 12q. MDM2 amplification inhibits p53, promoting tumor survival.

Question 5

A 17-year-old male with a history of a treated proximal humerus chondroblastoma presents 3 years later for routine follow-up. A chest CT reveals three small, asymptomatic bilateral pulmonary nodules. Biopsy of a nodule shows benign-appearing chondroblasts identical to the primary tumor. What is the most appropriate management?

Explanation

Chondroblastomas can rarely produce 'benign' pulmonary implants (1-2% of cases). These implants do not behave like true malignancies and have an excellent prognosis; they are typically managed with surgical resection or observation.

Question 6

Which of the following epigenetic alterations is highly specific for diagnosing chondroblastoma and distinguishing it from other giant cell-rich bone lesions?

Explanation

The H3F3B K36M mutation is found in approximately 90-95% of chondroblastomas. In contrast, the H3F3A G34W mutation is characteristic of giant cell tumors of bone.

Question 7

A 50-year-old female presents with a 15 cm deep, painless thigh mass.

MRI shows a predominantly fatty tumor with thick, nodular septations (>2 mm) and areas of non-lipogenic enhancement. What is the most appropriate definitive surgical approach?

Explanation

The imaging findings indicate a malignant fatty tumor, likely a liposarcoma. The standard of care for deep soft tissue sarcomas of the extremity is wide local excision with negative margins, often combined with radiation therapy.

Question 8

Which subtype of liposarcoma is unique in its tendency to spread to extrapulmonary sites, specifically necessitating a whole-spine MRI during initial staging to rule out bone metastases?

Explanation

Myxoid liposarcoma has a uniquely high propensity to metastasize to extrapulmonary sites, particularly the spine. Staging protocols for myxoid liposarcoma mandate an MRI of the entire spine.

Question 9

A 35-year-old male with untreated syringomyelia presents with massive swelling, instability, and crepitus of his right shoulder. He reports minimal pain despite severe radiographic destruction of the glenohumeral joint. What is the underlying pathophysiology of his joint destruction?

Explanation

The patient has a Charcot (neuropathic) joint of the shoulder, classically associated with syringomyelia. The loss of pain and proprioceptive sensation leads to repetitive microtrauma and severe joint destruction.

Question 10

A 16-year-old undergoes curettage of a presumed chondroblastoma.

Pathology shows areas of typical chondroblastoma juxtaposed with multiple blood-filled spaces lined by fibrous septa containing giant cells. What does this secondary finding represent?

Explanation

Secondary aneurysmal bone cysts (ABCs) occur in up to 15-20% of chondroblastomas. Histologically, they present as blood-filled spaces lacking an endothelial lining, but they do not alter the benign nature of the primary tumor.

Question 11

A 68-year-old male undergoes resection of a retroperitoneal sarcoma. Pathology reveals an abrupt transition from a well-differentiated liposarcoma to a high-grade, non-lipogenic pleomorphic sarcoma. What is the diagnosis?

Explanation

Dedifferentiated liposarcoma is characterized by the abrupt histological transition from a well-differentiated liposarcoma to a high-grade non-lipogenic sarcoma. It shares the same MDM2/CDK4 amplification as its well-differentiated counterpart.

Question 12

A 9-year-old boy presents with an atypical right thoracic scoliosis curve of 45 degrees. MRI confirms a large syringomyelia spanning C5 to T8 and a Chiari I malformation. What is the most appropriate initial surgical intervention?

Explanation

In patients with scoliosis secondary to syringomyelia/Chiari I, neurosurgical decompression is the recommended first step. Decompression often halts curve progression and may even improve the scoliosis in younger children with flexible curves.

Question 13

When differentiating atypical lipomatous tumor (ALT) from well-differentiated liposarcoma (WDL), which of the following is the primary distinguishing factor according to the WHO classification?

Explanation

ALT and WDL are morphologically and genetically identical (MDM2 amplified). The terminology is based on anatomic location: ALT is used for extremity/trunk tumors (where complete excision prevents recurrence), while WDL is used for deep locations like the retroperitoneum where local recurrence can be fatal.

Question 14

An 18-year-old female presents with shoulder pain. Imaging shows a lytic epiphyseal lesion in the proximal humerus with a sclerotic rim. Which of the following immunohistochemical markers would be most helpful in confirming the diagnosis of chondroblastoma?

Explanation

Chondroblastoma cells consistently express S-100 and SOX9, reflecting their chondroid lineage. Cytokeratin is for carcinomas, CD34 for vascular tumors, and Desmin/SMA for muscle tumors.

Question 15

A 75-year-old female presents with a rapidly growing, painful thigh mass. Biopsy demonstrates a high-grade sarcoma with numerous pleomorphic lipoblasts and complex karyotype with severe aneuploidy. There is no MDM2 amplification or t(12;16) translocation. What is the most likely diagnosis?

Explanation

Pleomorphic liposarcoma is the rarest and most aggressive subtype, characterized by complex karyotypes lacking the specific translocations or gene amplifications (like MDM2) seen in other liposarcomas.

Question 16

Which specific spinal cord tract is initially compromised in syringomyelia, leading to the classic 'cape-like' neurological deficit?

Explanation

Syringomyelia begins as a central dilation of the spinal canal. It first compresses the crossing pain and temperature fibers of the spinothalamic tract located in the anterior white commissure.

Question 17

A 16-year-old male with an open proximal femur physis presents with a symptomatic chondroblastoma crossing the physis into the metaphysis. How does this transphyseal involvement affect the surgical approach and prognosis?

Explanation

Chondroblastomas can cross the open physis. The treatment remains extended curettage; however, careful technique is required, and parents must be counseled on the high risk of iatrogenic physeal damage and subsequent growth arrest.

Question 18

Regarding the radiation sensitivity of liposarcoma subtypes, which variant is considered highly radiosensitive and often exhibits dramatic tumor shrinkage following neoadjuvant radiation therapy?

Explanation

Myxoid liposarcoma is exquisitely radiosensitive. Neoadjuvant radiation often leads to significant tumor shrinkage, making subsequent surgical resection easier.

Question 19

A 40-year-old male presents with hip pain. Radiographs show a lytic lesion in the femoral head epiphysis. Biopsy shows large cells with clear cytoplasm and distinct cell membranes, amidst a cartilaginous matrix. What is the most important differential diagnosis to distinguish from chondroblastoma in this older age group?

Explanation

Clear cell chondrosarcoma typically presents in the epiphysis of long bones in adults (30-50 years old), whereas chondroblastoma presents in the epiphysis of adolescents. Clear cell chondrosarcoma requires wide resection, unlike the curettage used for chondroblastoma.

Question 20

A 14-year-old female presents with scoliosis. On physical exam, stroking the skin around the umbilicus fails to elicit an umbilical deviation toward the stimulus on the left side. What is the significance of this finding in the context of adolescent idiopathic scoliosis?

Explanation

Asymmetric or absent abdominal reflexes are an objective 'hard' neurological sign in a patient with scoliosis. This finding strongly suggests an underlying intraspinal anomaly, such as syringomyelia, and mandates an MRI of the entire neuroaxis.

Question 21

A 45-year-old male presents with a deep, painless mass in his posterior thigh. Core needle biopsy demonstrates a myxoid stroma, scattered lipoblasts, and a prominent branching capillary network. Which cytogenetic abnormality is most characteristic of this tumor?

Explanation

The clinical and histologic description (myxoid stroma, chicken-wire vasculature, lipoblasts) is classic for myxoid liposarcoma. This tumor is characterized by the t(12;16) translocation, which fuses the FUS and DDIT3 genes.

Question 22

A 14-year-old boy presents with chronic knee pain. Radiographs reveal an eccentric, lytic lesion in the distal femoral epiphysis with a thin sclerotic rim.

Biopsy demonstrates mononuclear cells with grooved nuclei and areas of pericellular 'chicken-wire' calcification. What is the most appropriate definitive management?

Explanation

The presentation and histology are pathognomonic for a chondroblastoma, a benign but locally aggressive epiphyseal tumor. The standard of care is extended intralesional curettage, often augmented with a high-speed burr, followed by bone grafting or cementation.

Question 23

A 10-year-old girl is evaluated for a new-onset scoliosis. Physical examination reveals an atypical left-sided thoracic curve. Neurological examination reveals a loss of pain and temperature sensation in a cape-like distribution over her shoulders. What is the most appropriate next step in evaluation?

Explanation

A left-sided thoracic curve or a curve associated with neurologic deficits (such as the classic cape-like distribution of sensory loss) is highly suspicious for syringomyelia. A total spine MRI and brain MRI are required to evaluate for a syrinx and associated Chiari malformation.

Question 24

A 60-year-old man undergoes resection of a massive retroperitoneal tumor. Histology shows an abrupt transition between areas of well-differentiated adipocytic proliferation and areas of high-grade, non-lipogenic sarcoma. Which molecular marker is critically amplified in this pathology?

Explanation

This is a dedifferentiated liposarcoma, which typically arises from a well-differentiated liposarcoma, especially in the retroperitoneum. Both well-differentiated and dedifferentiated liposarcomas are characterized by the amplification of MDM2 and CDK4 on chromosome 12.

Question 25

A patient with a known history of an expanding syringomyelia in the cervical and thoracic spine begins to experience progressive flaccid paralysis and significant muscle atrophy in the intrinsic muscles of the hands. This specific physical finding indicates extension of the syrinx into which spinal cord structure?

Explanation

While central cord expansion initially damages the crossing spinothalamic fibers (causing loss of pain/temp), further expansion into the anterior horns damages lower motor neurons. This results in flaccid paralysis, atrophy, and fasciculations in the upper extremities.

Question 26

A 16-year-old boy presents with progressive shoulder pain. Radiographs demonstrate an epiphyseal lesion in the proximal humerus. Biopsy confirms chondroblastoma. Two years after successful curettage, routine imaging reveals three small, asymptomatic lung nodules. Biopsy of a lung nodule shows histologically benign chondroblastoma. What is the most appropriate management?

Explanation

Chondroblastoma is a benign tumor that can rarely produce 'benign metastases' to the lungs (1-2% of cases). The standard treatment for these lung lesions is surgical resection, which generally provides an excellent prognosis and is often curative.

Question 27

You are treating a 45-year-old patient diagnosed with myxoid liposarcoma of the proximal thigh. In addition to local imaging and a chest CT, what additional imaging modality is uniquely indicated for staging this specific sarcoma subtype?

Explanation

Myxoid liposarcoma has a unique propensity to metastasize to extrapulmonary sites, particularly the spine and bone, even before lung metastases appear. Whole spine MRI is recommended as part of the initial staging workup for this subtype.

Question 28

A 35-year-old woman with an untreated Chiari I malformation and large cervical syringomyelia presents with rapid, painless swelling of her right shoulder, accompanied by a 'crunching' sensation during movement. Radiographs reveal severe destruction of the humeral head and glenoid with loose osseous debris. What is the underlying pathophysiology of this joint destruction?

Explanation

The patient has developed neuropathic (Charcot) arthropathy of the shoulder, a classic complication of syringomyelia. The loss of protective sensation and proprioception leads to repeated microtrauma and subsequent rapid joint destruction.

Question 29

Histological examination of a well-differentiated liposarcoma (atypical lipomatous tumor) reveals hyperchromatic, atypical stromal cells within mature adipose tissue. By what primary mechanism does the characteristic gene amplification in this tumor promote oncogenesis?

Explanation

Well-differentiated liposarcomas feature MDM2 amplification. The MDM2 protein binds to and ubiquitinates p53, leading to its degradation and functionally inhibiting the p53 tumor suppressor pathway, promoting unchecked cell proliferation.

Question 30

A 13-year-old girl is found to have a 60-degree progressive thoracic scoliosis associated with a large, symptomatic syringomyelia and a Chiari I malformation. What is the recommended surgical sequencing for her treatment?

Explanation

In a patient with scoliosis secondary to a syrinx/Chiari malformation, neurosurgical decompression is indicated first to decompress the neural axis. Spinal fusion performed without prior decompression carries an unacceptably high risk of neurologic injury during deformity correction.

Question 31

Which of the following locations is the most common site for a chondroblastoma to arise in a skeletally immature patient?

Explanation

Chondroblastomas almost exclusively arise in the epiphyses (or apophyses, like the greater trochanter) of long bones in skeletally immature patients. The distal femur, proximal tibia, and proximal humerus are the most common locations.

Question 32

A 55-year-old man presents with a deep intramuscular mass in his vastus lateralis. MRI demonstrates a predominantly lipomatous mass with several thick, nodular septations measuring 4 mm in width that show enhancement. What is the most appropriate management strategy?

Explanation

Thick (>2 mm), nodular, and enhancing septations in a lipomatous mass on MRI are highly suspicious for an atypical lipomatous tumor (ALT) / well-differentiated liposarcoma. A core needle biopsy is required to confirm the diagnosis prior to definitive wide surgical resection.

Question 33

A 15-year-old male undergoes intralesional curettage of a pathologically confirmed chondroblastoma of the proximal tibial epiphysis.

During the procedure, a secondary cystic, hemorrhagic, and multiloculated cavity is encountered adjacent to the primary tumor. What is the most likely diagnosis of this secondary lesion?

Explanation

Secondary aneurysmal bone cysts (ABCs) occur in up to 15-20% of chondroblastomas. They present as blood-filled, multiloculated cavities that often require concurrent aggressive curettage to prevent recurrence.

Question 34

Myxoid liposarcoma has a distinct clinical response to neoadjuvant therapy compared to most other high-grade soft tissue sarcomas. Which of the following best describes this characteristic response?

Explanation

Myxoid liposarcoma is uniquely radiosensitive among soft tissue sarcomas. Preoperative radiation therapy often leads to dramatic tumor shrinkage, improved surgical margins, and extensive hyalinization/necrosis on the final pathology specimen.

Question 35

A 16-year-old male athlete presents with chronic ankle pain. Radiographs show a lytic, geographically distinct lesion within the calcaneal apophysis.

Histology demonstrates mononuclear cells with longitudinal nuclear grooves ('coffee bean' nuclei). Which highly specific epigenetic mutation is most strongly associated with this neoplasm?

Explanation

Chondroblastoma is driven by a highly specific histone H3 mutation: H3F3B K36M, which is present in over 90% of cases. The other options refer to different tumors (IDH1 in enchondroma/chondrosarcoma, G34W in giant cell tumor, GNAS in fibrous dysplasia).

Question 36

A 65-year-old woman presents with a rapidly enlarging, painless mass in her posterior thigh. Core needle biopsy demonstrates a high-grade sarcoma with pleomorphic lipoblasts, severe nuclear atypia, and a complex karyotype lacking any specific gene fusions or MDM2 amplification. What is the most likely diagnosis?

Explanation

Pleomorphic liposarcoma is the rarest and most aggressive subtype. Unlike other subtypes, it lacks specific translocations (like t(12;16) in myxoid) or amplifications (MDM2 in well-differentiated/dedifferentiated) and is characterized by a complex karyotype and high metastatic potential.

Question 37

In the classical neurological presentation of syringomyelia, the loss of pain and temperature sensation occurs bilaterally across the shoulders and upper extremities. This specific deficit results from the syrinx compressing which of the following?

Explanation

The syrinx typically begins in the central canal and expands outward. The first fibers it disrupts are the spinothalamic tract fibers that are decussating (crossing) in the anterior white commissure, leading to a bilateral loss of pain and temperature sensation at the level of the lesion.

Question 38

Which of the following clinical presentations is the most common initial symptom in a patient with a chondroblastoma?

Explanation

Because chondroblastomas are located in the epiphysis close to the articular surface, they most commonly present with joint pain, decreased range of motion, and a secondary sympathetic joint effusion. Pathologic fractures are rare.

Question 39

Which anatomical location carries the highest risk for an atypical lipomatous tumor (ALT) to undergo transformation into a dedifferentiated liposarcoma?

Explanation

Atypical lipomatous tumors (ALTs) and well-differentiated liposarcomas (WDLPS) are morphologically identical. The retroperitoneum carries the highest risk (up to 20%) of dedifferentiation due to the difficulty in achieving complete surgical margins and longer times to symptomatic presentation.

Question 40

A 10-year-old boy presents to the clinic with an isolated finding of diminished abdominal reflexes and mild hyperreflexia in the lower extremities. Further workup reveals a cervical syringomyelia. The presence of hyperreflexia in the lower extremities indicates that the syrinx has expanded to compress which structure?

Explanation

While syrinx expansion into the anterior horns causes lower motor neuron signs (flaccid paralysis/areflexia) at the level of the lesion, lateral expansion into the corticospinal tracts causes upper motor neuron signs (hyperreflexia, spasticity) below the level of the lesion.

Question 41

Which of the following chromosomal translocations is highly characteristic of myxoid liposarcoma?

Explanation

Myxoid liposarcoma is characterized by the t(12;16)(q13;p11) translocation, resulting in the FUS-DDIT3 fusion gene in over 90% of cases. A variant t(2;12) EWSR1-DDIT3 translocation is seen in the remaining cases.

Question 42

A 15-year-old boy presents with right knee pain. Radiographs reveal a well-defined lytic lesion in the proximal tibial epiphysis with a thin sclerotic margin. Biopsy demonstrates mononuclear cells, scattered multinucleated giant cells, and areas of pericellular calcification. What is the most appropriate initial management?

Explanation

The clinical and histological presentation is classic for a chondroblastoma. The standard of care is aggressive intralesional curettage, burring, and bone grafting, which offers high cure rates while preserving the joint.

Question 43

A 45-year-old female presents with progressive, painless swelling and instability of her right shoulder. Examination reveals massive crepitus and a loss of pain and temperature sensation over her shoulders and upper back. What is the most appropriate imaging modality to confirm the underlying etiology of her joint pathology?

Explanation

The patient has a Charcot (neuropathic) shoulder secondary to syringomyelia, indicated by her "cape-like" distribution of dissociated sensory loss. MRI of the cervical and thoracic spine is the gold standard to visualize the syrinx cavity.

Question 44

A deep-seated, 8 cm thigh mass in a 60-year-old man is biopsied, revealing an atypical lipomatous tumor (well-differentiated liposarcoma). Which of the following molecular markers is most consistently amplified in this pathology?

Explanation

Well-differentiated liposarcomas (atypical lipomatous tumors) and dedifferentiated liposarcomas are characterized by ring chromosomes and giant rod chromosomes leading to the amplification of MDM2 and CDK4 on chromosome 12q13-15.

Question 45

In a patient diagnosed with chondroblastoma of the proximal humerus, what specific histological feature is considered pathognomonic for this lesion?

Explanation

Chondroblastoma typically features mononuclear chondroblasts, osteoclast-like giant cells, and islands of eosinophilic chondroid matrix. The presence of fine, lace-like pericellular calcifications (the "chicken wire" pattern) is pathognomonic.

Question 46

Neuropathic (Charcot) arthropathy of the upper extremity, particularly affecting the shoulder or elbow, is most commonly associated with which of the following underlying conditions?

Explanation

While diabetes is the most common cause of Charcot joints in the foot and ankle, syringomyelia is the most common cause of neuropathic arthropathy in the upper extremities (shoulder and elbow) due to central cord disruption.

Question 47

What is the primary definitive treatment for a 10 cm dedifferentiated liposarcoma located deep within the posterior compartment of the thigh without evidence of systemic metastasis?

Explanation

Dedifferentiated liposarcoma is a high-grade soft tissue sarcoma. The standard of care for a localized, deep, high-grade soft tissue sarcoma of the extremity is wide surgical resection typically combined with (neoadjuvant or adjuvant) radiation therapy.

Question 48

A 17-year-old male undergoes curettage for a proximal femur chondroblastoma. Two years later, routine imaging reveals asymptomatic 1 cm bilateral pulmonary nodules. Biopsy of a nodule confirms benign-appearing chondroblastoma. What is the most appropriate management?

Explanation

Chondroblastoma can occasionally produce "benign" pulmonary metastases (occurring in 1-2% of cases) that are histologically identical to the primary tumor. Surgical resection of these nodules is the treatment of choice and carries an excellent prognosis.

Question 49

A 55-year-old presents with a painless, enlarging thigh mass. Histology demonstrates mature adipocytes with variation in cell size, scattered hyperchromatic stromal cells, and lipoblasts. Molecular testing is positive for CDK4 amplification. What is the most likely diagnosis?

Explanation

The histological description of mature fat with hyperchromatic, atypical stromal cells and lipoblasts, combined with CDK4 (and MDM2) amplification, is diagnostic of well-differentiated liposarcoma (atypical lipomatous tumor).

Question 50

Which physical examination finding is classically associated with the expanding central cord lesion seen in advanced syringomyelia?

Explanation

Syringomyelia causes an expanding central syrinx that primarily affects the crossing spinothalamic tracts. This results in "dissociated sensory loss," where pain and temperature sensation are lost (often in a cape-like distribution) but light touch and proprioception (dorsal columns) remain intact.

Question 51

A 16-year-old female presents with hip pain. Radiographs reveal a well-circumscribed, lytic lesion in the greater trochanter with a thin sclerotic rim. Which of the following immunohistochemical markers is characteristically positive in the mononuclear cells of this tumor?

Explanation

The lesion is a chondroblastoma (presenting in an apophyseal equivalent of an epiphysis). The mononuclear cells in chondroblastoma are characteristically positive for S-100 and DOG1.

Question 52

A 45-year-old patient presents with a large retroperitoneal mass identified as a dedifferentiated liposarcoma. Compared to well-differentiated liposarcoma, the dedifferentiated subtype is most strongly associated with which of the following?

Explanation

Dedifferentiated liposarcoma represents progression to a high-grade, non-lipogenic sarcoma. It behaves far more aggressively than well-differentiated liposarcoma, with significantly higher rates of both local recurrence and distant metastasis.

Question 53

Which of the following is the most common anatomic location for the development of a chondroblastoma?

Explanation

Chondroblastomas almost exclusively arise in the epiphyses or apophyses of long bones in skeletally immature patients. The distal femur epiphysis is the single most common site, followed by the proximal tibia and proximal humerus.

Question 54

A 32-year-old male with a known Chiari I malformation presents with weakness in his intrinsic hand muscles and multiple painless burn scars on his forearms. What is the precise pathophysiological mechanism responsible for his sensory deficit?

Explanation

The patient has syringomyelia, common in Chiari I malformations. The syrinx expands centrally in the spinal cord, first damaging the decussating spinothalamic fibers in the anterior white commissure, causing bilateral loss of pain and temperature sensation.

Question 55

Pleomorphic liposarcoma is the rarest and most aggressive subtype of liposarcoma. Unlike well-differentiated and myxoid liposarcomas, molecular analysis of a pleomorphic liposarcoma typically exhibits:

Explanation

Pleomorphic liposarcoma is a high-grade sarcoma characterized by complex, chaotic, and unbalanced karyotypes. It lacks the specific MDM2 amplifications seen in well-differentiated/dedifferentiated types and the FUS-DDIT3 translocations seen in the myxoid type.

Question 56

While performing an intralesional curettage of a chondroblastoma in the proximal humerus of a 14-year-old patient, the surgeon must be particularly careful to avoid iatrogenic damage to which of the following structures?

Explanation

Because chondroblastomas are epiphyseal lesions that typically occur in patients with open growth plates, surgical curettage risks damaging the adjacent physis, which can result in premature growth arrest or limb deformity.

Question 57

A 38-year-old female presents with a deep thigh mass that is confirmed by biopsy to be a myxoid liposarcoma. This specific sarcoma subtype has a unique predilection for metastasis to which of the following locations, necessitating specific staging studies?

Explanation

Unlike most other soft tissue sarcomas which metastasize primarily to the lungs, myxoid liposarcoma has a strong predilection for extrapulmonary metastasis, particularly to other soft tissue sites, the retroperitoneum, and the axial skeleton (spine). Staging must include whole spine/pelvis MRI.

Question 58

A 50-year-old woman develops a rapidly progressive, destructive arthropathy of her right elbow without significant trauma. Neurological exam reveals absent reflexes and cape-like sensory loss. MRI confirms a large cervical syrinx. What is the most appropriate initial management for her elbow?

Explanation

The patient has a Charcot elbow secondary to syringomyelia. Surgical interventions like arthroplasty, arthrodesis, or ORIF in Charcot joints have notoriously high failure and complication rates. Initial management involves bracing/protection and neurosurgical evaluation of the syrinx.

Question 59

A well-circumscribed, radiolucent lesion is found in the calcaneus of a 22-year-old patient. Biopsy confirms chondroblastoma. What makes the calcaneus and other tarsal bones unique regarding the anatomical predilection of chondroblastoma?

Explanation

Chondroblastomas prefer epiphyseal locations. In the foot and ankle, the tarsal bones (especially the calcaneus and talus) are considered epiphyseal or apophyseal equivalents, making them classic locations for this tumor outside the long bones.

Question 60

Which subtype of liposarcoma is characterized histologically by a prominent branching capillary network resembling a "chicken-wire" vascular pattern, abundant mucinous stroma, and small lipoblasts?

Explanation

Myxoid liposarcoma is histologically characterized by a rich, delicate, arborizing capillary network often described as a "chicken-wire" or "crow's feet" vascular pattern, set in a myxoid (mucinous) stroma with lipoblasts.

Question 61

A 15-year-old male presents with chronic knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion in the proximal tibia with a sclerotic rim. Biopsy reveals mononuclear cells with clefted nuclei and a distinct "chicken-wire" pattern of calcification.

What is the most appropriate management for this lesion?

Explanation

This is a classic presentation of a chondroblastoma, an epiphyseal lesion found in skeletally immature patients. Histology demonstrates mononuclear cells with grooved nuclei and "chicken-wire" calcifications. The gold standard treatment is aggressive extended curettage (often with chemical/mechanical adjuvants) and bone grafting.

Question 62

A 45-year-old male presents with a deep, painless thigh mass. Histopathologic examination reveals uniform, small round cells in a myxoid stroma with a prominent, arborizing "crow's feet" capillary network. Which of the following cytogenetic abnormalities is pathognomonic for this tumor?

Explanation

The diagnosis is myxoid liposarcoma, characterized by small round cells, a myxoid background, and a delicate arborizing capillary network. The defining genetic alteration is the t(12;16) translocation, which creates the FUS-DDIT3 fusion protein.

Question 63

An 8-year-old male presents with a rapidly progressive left thoracic scoliosis curve of 45 degrees. On neurological examination, he has absent superficial abdominal reflexes on the left side but normal lower extremity motor strength. What is the most appropriate next step in management?

Explanation

A left-sided thoracic scoliosis curve and asymmetric/absent abdominal reflexes in a young child are "red flags" indicating a potential underlying intraspinal anomaly, such as syringomyelia or Chiari malformation. An MRI of the entire spine and hindbrain is mandatory before considering any deformity correction.

Question 64

A 60-year-old patient undergoes resection of a massive retroperitoneal tumor. Histology shows mature adipose tissue with scattered highly atypical, hyperchromatic stromal cells. Fluorescence in situ hybridization (FISH) confirms the diagnosis of a well-differentiated liposarcoma. Which gene amplification was detected?

Explanation

Well-differentiated liposarcomas (and their dedifferentiated counterparts) are characterized by supernumerary ring chromosomes that result in the amplification of MDM2 and CDK4 on chromosome 12q13-15. This amplification helps differentiate it from benign lipomas.

Question 65

A 17-year-old male undergoes curettage of a distal femur chondroblastoma. Two years later, routine surveillance imaging reveals three small pulmonary nodules. Biopsy of a lung nodule confirms cells identical to the primary tumor. What is the expected clinical behavior of these lung lesions?

Explanation

Chondroblastoma is a benign tumor but is unique in its ability to rarely produce "benign pulmonary metastases." These implants are histologically identical to the primary tumor and are typically successfully treated with complete surgical resection, yielding excellent long-term survival.

Question 66

A 45-year-old female presents with painless swelling, crepitus, and instability of the right shoulder. Radiographs show severe destruction of the glenohumeral joint with massive osseous debris but no signs of infection. Neurological exam reveals a loss of pain and temperature sensation in the upper extremities. What is the primary pathophysiology?

Explanation

This patient has neuropathic (Charcot) arthropathy of the shoulder secondary to syringomyelia. Cavitation of the central spinal cord (syrinx) damages crossing spinothalamic tracts in the anterior white commissure, leading to the classic "cape-like" loss of pain and temperature.

Question 67

A 35-year-old male is newly diagnosed with myxoid liposarcoma of the posterior thigh. When planning staging workup for this specific histologic subtype, which of the following is true regarding its metastatic pattern?

Explanation

Unlike most other high-grade soft tissue sarcomas that metastasize primarily to the lungs, myxoid liposarcoma is unique for its tendency to metastasize to extrapulmonary bone and soft tissues, particularly the spine. Staging protocols typically include an MRI of the entire spine.

Question 68

Histological evaluation of a curettage specimen from a proximal humerus lesion reveals sheets of mononuclear cells with "coffee-bean" nuclei, interspersed osteoclast-like giant cells, and delicate pericellular calcifications.

This constellation of findings is diagnostic for:

Explanation

The histological triad of mononuclear cells with clefted ("coffee-bean") nuclei, scattered osteoclast-like giant cells, and "chicken-wire" (pericellular) calcifications is pathognomonic for chondroblastoma.

Question 69

In the pediatric population, a symptomatic syrinx (syringomyelia) causing a rapidly progressive scoliosis is most commonly associated with which of the following underlying cranial abnormalities?

Explanation

Syringomyelia in children is predominantly associated with a Chiari I malformation, where the cerebellar tonsils herniate through the foramen magnum. This alters CSF dynamics, leading to the formation of a syrinx within the spinal cord.

Question 70

A 65-year-old female presents with a massive, painless thigh mass. Core biopsy reveals an abrupt transition from a well-differentiated, lipoma-like tumor to a high-grade, non-lipogenic sarcoma.

Which of the following statements is true regarding this specific entity?

Explanation

This describes dedifferentiated liposarcoma, which represents high-grade progression of a well-differentiated liposarcoma. Importantly, both well-differentiated and dedifferentiated liposarcomas share the exact same genetic hallmark: amplification of the MDM2 and CDK4 genes.

Question 71

While chondroblastomas classically occur in the epiphysis of long bones, they can also arise in apophyseal equivalents. Which of the following is the most common apophyseal location for a chondroblastoma?

Explanation

The greater trochanter of the femur and the greater tuberosity of the humerus are apophyses (epiphyseal equivalents) and represent classic anatomical locations for apophyseal chondroblastomas.

Question 72

A 12-year-old girl with syringomyelia and an associated Chiari I malformation presents with a 60-degree progressive thoracic scoliosis. Which of the following describes the recommended sequence of surgical interventions?

Explanation

To minimize the risk of devastating neurological complications during deformity correction, neurosurgical intervention (suboccipital decompression) for the Chiari malformation/syrinx must be performed before addressing the scoliosis.

Question 73

Among the main histological subtypes of liposarcoma, which carries the worst overall prognosis, highest rate of metastasis, and is characterized by a complex karyotype lacking a specific, defining chromosomal translocation?

Explanation

Pleomorphic liposarcoma is the rarest and most aggressive subtype. It presents as a high-grade pleomorphic sarcoma with complex karyotypes (lacking specific translocations or MDM2 amplifications) and has the highest rate of distant metastasis and lowest survival.

Question 74

Due to a local recurrence rate of 10-20% following simple curettage of a chondroblastoma, modern surgical management routinely incorporates an extended curettage. Which of the following combinations is typically utilized in the surgical bed?

Explanation

To reduce local recurrence of chondroblastoma, extended curettage utilizing a high-speed burr to break through the reactive bone, followed by chemical/thermal adjuvants like phenol, hydrogen peroxide, or cryotherapy, is standard prior to bone grafting or PMMA.

Question 75

A 28-year-old male with a known cervical syrinx presents with painless burns on his hands. He has normal light touch and proprioception bilaterally. The pathophysiology of his isolated sensory deficit is due to compression of which specific spinal cord structure?

Explanation

A centrally expanding syrinx initially compresses the anterior white commissure, where the second-order neurons of the lateral spinothalamic tracts decussate. This selective damage results in a bilateral loss of pain and temperature sensation while preserving the dorsal columns (light touch/proprioception).

Question 76

When evaluating a deep soft tissue mass of the thigh on MRI, which of the following imaging characteristics is highly suggestive of a well-differentiated liposarcoma rather than a benign lipoma?

Explanation

Well-differentiated liposarcoma shares the bright T1 signal of fat seen in benign lipomas but is distinguished by the presence of thick (>2mm), nodular, and contrast-enhancing internal septations.

Question 77

A 14-year-old patient presents with a large joint effusion and severe shoulder pain. Radiographs demonstrate a radiolucent lesion in the proximal humeral epiphysis. MRI confirms the lesion and surrounding bone marrow edema.

Which local complication is highly associated with chondroblastoma and likely causing the profound joint effusion?

Explanation

Chondroblastomas are intensely inflammatory tumors that cause extensive surrounding marrow edema and reactive joint effusions. Additionally, up to 15-20% of chondroblastomas develop secondary aneurysmal bone cysts (ABCs), exacerbating pain and swelling.

Question 78

A 55-year-old male presents with a large, deep intramuscular mass in the vastus lateralis. Core needle biopsy confirms dedifferentiated liposarcoma. Staging scans show no evidence of distant metastasis.

What is the most appropriate definitive management?

Explanation

Dedifferentiated liposarcoma of the extremity is a high-grade soft tissue sarcoma. The gold standard for localized high-grade extremity soft tissue sarcoma is wide surgical resection (negative margins) combined with neoadjuvant or adjuvant radiation therapy to optimize local control.

Question 79

A 40-year-old male presents with cape-like pain and temperature sensory loss in the upper extremities. MRI of the cervical spine reveals a syrinx extending from C2 to T2. However, there is no evidence of a Chiari malformation, spinal tumor, or tethered cord. What is the most likely anamnestic finding in this patient's history?

Explanation

When a syrinx is found without an associated congenital anomaly (like Chiari malformation) or tumor, it is often acquired. Prior severe spinal cord trauma or an inflammatory process (meningitis/arachnoiditis) alters normal CSF dynamics, leading to secondary syrinx formation.

Question 80

A pathologist is evaluating a curettage specimen from a distal femur epiphyseal lesion. The differential diagnosis is primarily between chondroblastoma and giant cell tumor of bone. Which of the following combinations of immunohistochemical markers and genetic mutations is highly specific for chondroblastoma?

Explanation

Chondroblastomas are of cartilaginous origin and express S-100. More specifically, recent molecular pathology has identified the H3.3 K36M mutation (a histone H3.3 gene mutation) as highly specific for chondroblastoma, differentiating it from giant cell tumor of bone (which has the H3F3A G34W mutation).

Question 81

A 14-year-old boy presents with chronic right knee pain. Radiographs reveal a well-circumscribed, lytic lesion with a thin sclerotic rim located centrally in the distal femoral epiphysis. Biopsy demonstrates mononuclear cells with longitudinal nuclear grooves and scattered multinucleated giant cells within a background of pericellular 'chicken-wire' calcification. What is the most appropriate primary surgical treatment for this lesion?

Explanation

The clinical and histologic findings are diagnostic of chondroblastoma, a benign but locally aggressive epiphyseal tumor. Extended intralesional curettage with high-speed burring and filling the defect with bone graft or cement is the standard of care to minimize recurrence while preserving the joint.

Question 82

A 45-year-old male presents with a painless, deep thigh mass. MRI reveals a multinodular intramuscular mass with high T2 signal and linear septations. Core needle biopsy confirms myxoid liposarcoma. Which of the following chromosomal translocations is most characteristic of this tumor?

Explanation

Myxoid liposarcoma is classically associated with the t(12;16) translocation, which results in the FUS-DDIT3 fusion gene in over 90% of cases. Identifying this translocation is crucial for definitive diagnosis and helps differentiate it from other myxoid soft tissue tumors.

Question 83

A 28-year-old female presents with a progressive left-sided thoracic scoliosis and decreased pain and temperature sensation in her bilateral upper extremities. Light touch and proprioception remain intact. Which of the following is the most appropriate next step in her evaluation?

Explanation

Dissociated sensory loss (loss of pain/temperature with preserved dorsal column function) and an atypical left-sided thoracic scoliotic curve strongly suggest syringomyelia. An MRI of the entire neuroaxis is required to evaluate for a syrinx and associated congenital anomalies like a Chiari malformation.

Question 84

A 15-year-old male undergoes extended curettage of a proximal humeral epiphyseal lesion confirmed as chondroblastoma.

During his 2-year follow-up, a routine chest CT reveals a solitary 1.2 cm pulmonary nodule. A biopsy of the nodule shows identical histology to the primary bone tumor. What is the most appropriate management?

Explanation

Chondroblastoma can occasionally produce 'benign' pulmonary metastases, occurring in 1-2% of cases. These metastases typically behave indolently, and surgical resection of the lung nodules is frequently curative, providing an excellent long-term prognosis.

Question 85

An asymptomatic 60-year-old woman undergoes imaging for a suspected hematoma, revealing a deep intramuscular lipomatous mass in her anterior thigh measuring 12 cm. Core needle biopsy demonstrates mature adipocytes with focal hyperchromatic nuclei and nuclear atypia. Molecular testing is most likely to show amplification of which of the following?

Explanation

Well-differentiated liposarcoma (atypical lipomatous tumor) is characterized by the amplification of the MDM2 and CDK4 genes on chromosome 12q13-15. This molecular finding reliably distinguishes it from benign deep lipomas.

Question 86

A 12-year-old boy presents with a rapidly progressive right thoracic scoliosis measuring 55 degrees. An MRI demonstrates a large cervicothoracic syrinx and a Chiari I malformation. What is the most appropriate recommended treatment sequence?

Explanation

In patients with a syrinx and significant scoliosis, neurosurgical decompression of the Chiari malformation/syrinx must precede orthopedic spinal deformity correction. Decompression alone may halt progression or even improve the scoliotic curve, particularly in younger patients.

Question 87

A 32-year-old female presents with a slowly enlarging, firm mass in her posterior thigh.

Histology shows uniform spindle cells in a collagenous stroma without significant atypia or necrosis. Immunohistochemistry is strongly positive for nuclear beta-catenin. Given the diagnosis, what is the preferred initial management strategy?

Explanation

The diagnosis is extra-abdominal aggressive fibromatosis (desmoid tumor), confirmed by nuclear beta-catenin positivity. Because these tumors lack metastatic potential, frequently recur after surgery, and often spontaneously stabilize or regress, active observation is now the first-line management for asymptomatic patients.

Question 88

A 65-year-old man presents with a rapidly growing, painful soft tissue mass in his left thigh.

Histological examination reveals highly atypical, bizarre, multinucleated giant cells and lipoblasts with no well-differentiated areas. There are no specific genetic translocations identified. Which of the following statements regarding this subtype of liposarcoma is true?

Explanation

Pleomorphic liposarcoma is the least common but most aggressive subtype of liposarcoma. It is a high-grade tumor with complex karyotypes (lacking specific translocations or MDM2/CDK4 amplifications) and carries a high risk of early pulmonary metastasis and poor overall survival.

Question 89

When attempting to differentiate a chondroblastoma from a giant cell tumor of bone on core needle biopsy, which of the following histological or immunohistochemical features is most specific for chondroblastoma?

Explanation

Chondroblastoma is characterized by S-100 positive mononuclear chondroblasts and 'chicken-wire' pericellular calcification. Giant cell tumor of bone, conversely, is characterized by the H3F3A G34W mutation and lacks typical chondroid matrix or S-100 positivity.

Question 90

A 40-year-old male with a history of a chronic, untreated cervical syrinx presents with a massively swollen, painless right shoulder. Radiographs demonstrate severe joint destruction, bony debris, and disorganization of the glenohumeral joint. Infection is ruled out via aspiration. What is the fundamental pathophysiology driving this joint destruction?

Explanation

This patient has a neuropathic (Charcot) arthropathy of the shoulder, classically associated with syringomyelia in the upper extremity. The underlying mechanism is the disruption of pain and proprioceptive pathways, leading to unrecognized repetitive microtrauma and progressive joint destruction.

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

Master ABOS Orthopedic Board Review: Liposarcoma, Chondroblastoma, Syringomyelia | Part 17

Key Takeaway

Master ABOS Orthopedic Board Review: Liposarcoma, Chondroblastoma, Syringomyelia | Part 17

Chapter Index