Bone and Soft Tissue Pathology — MCQs

A 4-year-old boy is brought to the physician by his parents due to frequent falls, inability to jump, and easy fatigue. Physical examination reveals weakness in the pelvic and shoulder girdles, as well as enlargement of the child's calf muscles. The serum level of creatine kinase is elevated. A biopsy of calf muscle reveals marked variation in size and shape of muscle fibers, with foci of muscle fiber necrosis, myophagocytosis, regenerating fibers, and fibrosis. Molecular diagnostic assays performed on muscle biopsy from the patient would show alterations in the length of the primary transcript for which muscle-associated protein?

Q349

Histology of Myositis ossificans most closely mimics which of the following?

Q350

What is the gene fusion associated with Ewing's sarcoma?

Bone and Soft Tissue Pathology Indian Medical PG Practice Questions and MCQs

Question 341: Which of the following statements about desmoid tumors is incorrect?

A. Show infiltrative growth pattern
B. Often seen below the umbilicus
C. More common in women
D. Highly radiosensitive (Correct Answer)

Explanation: ***Highly radiosensitive*** - This is the **INCORRECT** statement and hence the correct answer to this question. - Desmoid tumors are **radioresistant**, not radiosensitive, meaning they do not respond well to radiation therapy. - Radiation therapy is typically reserved for cases where surgery is not feasible or for local control after incomplete resection, but it is not highly effective as a standalone treatment. - The radioresistant nature is an important clinical characteristic that influences treatment planning. *Often seen below the umbilicus* - This statement is **correct** about desmoid tumors. - Desmoid tumors frequently arise from the **anterior abdominal wall**, with a common location being below the umbilicus, particularly in postpartum women. - Abdominal wall desmoids are strongly associated with **pregnancy** and trauma, and can be locally aggressive. *Show infiltrative growth pattern* - This statement is **correct** about desmoid tumors. [1] - Desmoid tumors are characterized by their **locally aggressive** and infiltrative growth pattern, often invading adjacent tissues like muscle, fascia, and neurovascular structures. [1] - This infiltrative nature makes complete surgical resection challenging and contributes to a high rate of **local recurrence** (up to 20-40% after surgery). - Despite their aggressive local behavior, desmoid tumors do not metastasize. *More common in women* - This statement is **correct** about desmoid tumors. - Desmoid tumors show a **female predominance**, particularly affecting women during their reproductive years (ages 25-40). - This gender predilection is linked to **hormonal influences**, with increased risk during **pregnancy** and the postpartum period. - The association with estrogen is further supported by occasional tumor regression after menopause. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 691-692.

Question 342: Which of the following soft-tissue lesions has a biphasic histologic pattern and consists of cuboidal epithelial and spindle-shaped mesenchymal cells?

A. Synovial sarcoma (Correct Answer)
B. Nodular fasciitis
C. Liposarcoma
D. Malignant fibrous histiocytoma

Explanation: *Liposarcoma* - Typically presents with **lipoblasts** and does not exhibit a **biphasic histologic pattern**. - Usually lacks **cuboidal epithelial** cells, focusing instead on adipose tissue differentiation. *Nodular fasciitis* [2] - This is a reactive benign lesion characterized by **plump fibroblasts** and **myofibroblasts**, not a malignant neoplasm. - The histological pattern is **monophonic** and does not feature **epithelial components**. *Synovial sarcoma* [1] - Though it can present with a biphasic pattern, it is characterized by **monomorphic spindle cells** and does not consistently show **epithelial components** like cuboidal cells. - Typically associated with **SS18-SSX fusion** genes, which is not an indication of just any malignant neoplasm. *Malignant fibrous histiocytoma* - Characterized by **histiocytic and spindle cell** components but lacks the **epithelial features** that define a biphasic pattern. - Primarily composed of **malignant fibrous histiocytoma**, which does not indicate a specific malignancy associated with epithelial differentiation. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1225-1226. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1223-1224.

Question 343: Which of the following is a marker for Ewing sarcoma?

A. SS18-SSX fusion
B. MDM2 amplification
C. EWSR1 gene fusion (Correct Answer)
D. None of the options

Explanation: ***EWSR1 gene fusion*** - **Ewing sarcoma** is characterized by specific chromosomal translocations involving the **EWSR1 gene** on chromosome 22, most commonly **t(11;22)(q24;q12)**, leading to an **EWSR1-FLI1 fusion gene**. - This fusion gene acts as an **aberrant transcription factor**, driving the oncogenesis and giving rise to the characteristic **small round blue cell tumor** morphology. *MDM2 amplification* - **MDM2 amplification** is a genetic alteration primarily associated with **atypical lipomatous tumors/well-differentiated liposarcoma** and **dedifferentiated liposarcoma**. - It is a marker used in the diagnosis of these specific soft tissue sarcomas and is not typically found in Ewing sarcoma. *SS18-SSX fusion* - The **SS18-SSX fusion gene** results from a characteristic chromosomal translocation **t(X;18)(p11.2;q11.2)** and is the defining genetic hallmark of **synovial sarcoma**. - This fusion gene is a critical diagnostic marker for synovial sarcoma and is not present in Ewing sarcoma. *None of the options* - This option is incorrect because **EWSR1 gene fusion** is a well-established and specific marker for Ewing sarcoma.

Question 344: Which of the following is a bone-forming malignant tumor?

A. Osteoid osteoma
B. Osteosarcoma (Correct Answer)
C. Chondroblastoma
D. Giant cell tumor

Explanation: ***Osteosarcoma*** - **Osteosarcoma** is the most common **primary malignant bone tumor**, characterized by the production of **osteoid** (immature bone) by malignant osteoblasts [1], [2]. - It typically arises in the **metaphysis of long bones** (e.g., distal femur, proximal tibia, proximal humerus) and often presents with pain and swelling [1], [2]. *Osteoid osteoma* - **Osteoid osteoma** is a benign bone tumor characterized by a small nidus of **osteoid-forming tissue** surrounded by sclerotic bone. - While it involves osteoid formation, it is **not malignant** and does not metastasize. *Chondroblastoma* - **Chondroblastoma** is a rare, **benign cartilage-forming tumor** that typically occurs in the **epiphysis of long bones** in skeletally immature individuals. - It is composed of chondroblast-like cells and does not produce osteoid or show malignant features. *Giant cell tumor* - **Giant cell tumor** of bone is an **aggressive, locally destructive benign tumor** characterized by numerous osteoclast-like giant cells and spindle-shaped stromal cells. - It arises in the **epiphysis/metaphysis** of long bones (e.g., distal femur, proximal tibia) but is not a bone-forming tumor and is typically not malignant, though it has a high recurrence rate. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 671-674. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1200-1202.

Question 345: The muscle which is affected last with Duchenne muscular dystrophy is-

A. Facial
B. Abdominal
C. Diaphragm
D. Ocular (Correct Answer)

Explanation: ***Ocular*** - The **extraocular muscles** are typically spared until the very late stages of Duchenne muscular dystrophy (DMD), making them among the last to be affected [1]. - This sparing is a characteristic feature that helps differentiate DMD from some other neuromuscular conditions. *Facial* - While facial muscles can be less severely affected compared to limb muscles, they do show involvement earlier than ocular muscles, contributing to a **mask-like facies** in advanced stages. - Weakness of facial muscles can lead to difficulties with smiling, whistling, and closing the mouth completely *Diaphragm* - The **diaphragm** is a crucial respiratory muscle, and its weakness in DMD is a major cause of **respiratory insufficiency** and mortality, usually occurring in the later stages of the disease progression [1]. - Diaphragmatic involvement typically manifests before ocular muscles are affected, often necessitating ventilatory support. *Abdominal* - **Abdominal muscles** are affected relatively early in the progression of DMD, contributing to difficulties with posture and compromised respiratory function due to poor cough effort. - Weakness in these muscles impacts core strength and stability, preceding the involvement of ocular muscles. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, pp. 1244-1245.

Question 346: Which bone is most commonly involved in Paget's disease?

A. Pelvis (Correct Answer)
B. Skull
C. Vertebrae
D. Femur

Explanation: ***Pelvis*** - The **pelvis** is the **most commonly involved bone** in Paget's disease, affected in approximately **60-70% of cases**. [1] - Patients may be **asymptomatic** or present with **pelvic pain**, difficulty walking, or hip problems. [1] - Complications include **acetabular protrusion**, secondary **osteoarthritis of the hip**, and pathological fractures. - The high frequency of pelvic involvement makes it the most characteristic site for this disease. *Femur* - The **femur** is the second most commonly affected bone, involved in approximately **55% of cases**. [1] - Presents with **anterior bowing** ("saber-shin" deformity when tibia is involved), bone pain, and increased risk of **pathological fractures** (classic "chalkstick" or "banana" fracture). [1] - Long bone involvement leads to deformities and gait disturbances. [2] *Skull* - The **skull** is affected in **25-65% of cases**, but is less common than the pelvis. - Leads to **frontal bossing**, enlarged head circumference (**increased hat size**), and **hearing loss** due to ossicle involvement or auditory nerve compression. [1] - Complications include **basilar invagination**, headaches, and rarely cranial nerve deficits. [1] *Vertebrae* - The **spine** (especially lumbar and sacral regions) is involved in approximately **50% of cases**. [1] - Causes **back pain**, **spinal stenosis**, **nerve root compression**, and **kyphosis**. [1] - Vertebral involvement increases the risk of **vertebral compression fractures** and neurological complications. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1192-1194. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 660-661.

Question 347: Which tumor is most commonly associated with radiation exposure?

A. Osteoblastoma
B. Ewing's sarcoma
C. Osteoclastoma
D. Osteosarcoma (Correct Answer)

Explanation: ***Osteosarcoma*** - **Osteosarcoma** is the most common primary bone tumor and is known to be associated with previous **radiation exposure**, particularly in patients who received radiotherapy for other cancers. - The risk of developing osteosarcoma increases with higher doses of **radiation**, especially when the bone is within the radiation field. *Osteoblastoma* - **Osteoblastoma** is a rare, benign bone tumor that is not typically associated with a history of **radiation exposure**. - It usually presents as localized pain and tenderness and is characterized by the formation of **osteoid tissue** and bone. *Ewing's sarcoma* - **Ewing's sarcoma** is a highly malignant bone tumor of neuroectodermal origin, most commonly affecting children and young adults. - While its exact etiology is unclear, it is not directly linked to **radiation exposure** but rather to specific **chromosomal translocations**, such as t(11;22)(q24;q12). *Osteoclastoma* - Also known as **giant cell tumor of bone**, osteoclastoma is a benign but locally aggressive tumor. - It is not known to be caused by **radiation exposure** but is characterized by its large, multinucleated giant cells resembling osteoclasts.

Question 348: A 4-year-old boy is brought to the physician by his parents due to frequent falls, inability to jump, and easy fatigue. Physical examination reveals weakness in the pelvic and shoulder girdles, as well as enlargement of the child's calf muscles. The serum level of creatine kinase is elevated. A biopsy of calf muscle reveals marked variation in size and shape of muscle fibers, with foci of muscle fiber necrosis, myophagocytosis, regenerating fibers, and fibrosis. Molecular diagnostic assays performed on muscle biopsy from the patient would show alterations in the length of the primary transcript for which muscle-associated protein?

A. Creatine kinase
B. Desmin
C. Dystrophin (Correct Answer)
D. Glycogen phosphorylase

Explanation: ***Dystrophin*** - The clinical features, including muscle weakness, calf muscle hypertrophy, and elevated **creatine kinase**, indicate a muscular dystrophy, most characteristically associated with **dystrophin** deficiency [1]. - **Muscle biopsy results** showing variation in muscle fiber size and necrosis further support the diagnosis of **Duchenne muscular dystrophy**, where dystrophin mutations are commonly identified [1]. *Desmin* - Although desmin is a muscle protein, it is primarily involved in **muscle fiber structure** and not directly associated with the symptoms or findings noted in this case. - Conditions linked to desmin abnormalities usually involve **myofibrillar myopathies**, which present differently than the scenario described here. *Glycogen phosphorylase* - Glycogen phosphorylase is crucial in **glycogen metabolism**, and its deficiency typically leads to metabolic myopathies presenting with **exercise intolerance** rather than the distinct symptoms of muscle necrosis seen here. - The muscle pathology observed (necrosis and regeneration) does not correlate with typical presentations seen in glycogen storage diseases. *Creatine kinase* - While creatine kinase levels are elevated in many muscle disorders, including dystrophies, it is not a structural protein and thus does not fit the question's focus on **primary transcript alterations** [2]. - Measuring creatine kinase assists in diagnosing muscle damage but does not indicate a molecular defect like **dystrophin**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, pp. 1244-1245. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, pp. 1245-1246.

Question 349: Histology of Myositis ossificans most closely mimics which of the following?

A. Giant Cell Tumor
B. Ewing's tumor
C. Osteochondroma
D. Osteosarcoma (Correct Answer)

Explanation: ***Osteosarcoma*** - Histologically, myositis ossificans can mimic **osteosarcoma**, as both conditions show features of **ossification and bone formation** [1]. - **Age** and **location** may also help differentiate, but careful histological examination reveals similarities. *Osteochondroma* - Characterized by a **cartilaginous cap** overlying the bone, which is not present in myositis ossificans [2]. - Usually develops in patients with a **pedunculated or sessile base**, rather than the heterogeneous ossification seen in myositis ossificans. *Ewing's tumour* - This is a **malignant round cell tumor** that predominantly affects children and young adults, with specific **translocation** genetic features. - Histologically, it shows a **small, blue cell appearance**, distinct from the fibroblastic reaction and bone formation seen in myositis ossificans. *GCT* - Granulosa cell tumors (GCT) are primarily **gynecological**, with no significant **bony changes** as seen in myositis ossificans. - Histologically, GCTs show **multinucleated giant cells** and are associated with **subarticular bone lesions**, unlike the heterotopic ossification seen in myositis ossificans. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 673-674. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 672-673.

Question 350: What is the gene fusion associated with Ewing's sarcoma?

A. EWS-FLI1 (Correct Answer)
B. FUS-CHOP
C. EWS-ATF1
D. PAX3-FOXO1

Explanation: ***EWS-FLI1*** * This is the **most common and characteristic gene fusion** found in Ewing's sarcoma, occurring in about 85% of cases. * The fusion involves the **Ewing sarcoma RNA-binding protein 1 (EWSR1)** gene on chromosome 22 and the **Friend leukemia integration 1 transcription factor (FLI1)** gene on chromosome 11. *PAX3* * **PAX3** gene fusions, particularly **PAX3-FOXO1**, are associated with **alveolar rhabdomyosarcoma**, a different type of soft tissue sarcoma. * While both are pediatric tumors, their genetic drivers and typical histologies differ significantly from Ewing's sarcoma. *FUS-CHOP* * The **FUS-CHOP (DDIT3)** gene fusion is characteristic of **myxoid liposarcoma**, a distinct type of adipocytic tumor. * This fusion involves the **FUS RNA binding protein (FUS)** gene and the **DNA damage inducible transcript 3 (DDIT3)** gene. *EWS-ATF1* * The **EWS-ATF1** gene fusion is a molecular hallmark of **clear cell sarcoma** (also known as malignant melanoma of soft parts). * This fusion involves the **EWSR1** gene and the **activating transcription factor 1 (ATF1)** gene, leading to distinct biological and clinical features compared to Ewing's sarcoma.

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