Bone and Soft Tissue Pathology Practice Questions

Q: A 10-year-old child with known hemophilia presents with ankle pain. X-ray shows a lytic lesion with sclerotic rim at the calcaneum. What is the most likely diagnosis?

Pseudotumor associated with bleeding disorders. ***Pseudotumor associated with bleeding disorders*** - A lytic lesion with a sclerotic rim in the **calcaneum** in a child with **hemophilia** is highly suggestive of a **hemophilic pseudotumor** due to repeated hemorrhage. - These lesions occur from recurrent **intraosseous bleeding** forming a hematoma that stimulates bone resorption and reactive sclerotic rim formation. - Hemophilic pseudotumors are **expansile, blood-filled cystic lesions** that can mimic neoplasms radiologically. - They are one of the most serious complications of hemophilia, requiring differentiation from malignancy. *Ochronosis* - Ochronosis is a rare metabolic disorder (alkaptonuria) characterized by deposition of **homogentisic acid polymer** in connective tissues. - It typically causes progressive **arthropathy** in adults with diffuse degenerative changes and disc calcifications, not a solitary lytic lesion in a child. *PVNS* - **Pigmented villonodular synovitis (PVNS)** is a benign proliferative disorder of the synovium. - It primarily affects the **synovial lining** of joints and tendon sheaths, causing joint erosions and soft tissue masses, but not typically a solitary intraosseous lytic lesion with sclerotic rim in the calcaneum. *Eumycosis* - **Eumycosis (eumycetoma)** is a chronic, progressively destructive fungal infection affecting subcutaneous tissues and bone. - Classical presentation involves **soft tissue swelling, sinus tracts, and grain discharge**, making it less likely in the absence of these features.

Q: At which of the following sites do osteoclasts remove bone?

Both Howship's lacunae and resorption bays.. ***Both Howship's lacunae and resorption bays.*** - **Howship's lacunae** and **resorption bays** are **synonymous terms** referring to the same anatomical structures - These are the **characteristic shallow depressions or pits** on bone surfaces where osteoclasts attach via their ruffled border and actively resorb bone [1] - Osteoclasts create an acidic microenvironment in these lacunae that dissolves the mineral matrix, followed by enzymatic digestion of the organic matrix [1] - Both terms are used interchangeably in histology and pathology to describe these sites of active bone resorption *Howship's lacunae* - This is an **incomplete answer** - while Howship's lacunae are indeed sites where osteoclasts remove bone, this option ignores that resorption bays refer to the same structures - Selecting only one term when both are synonymous makes this answer **technically incomplete** *Resorption bays* - This is also an **incomplete answer** - resorption bays are correct sites of osteoclastic bone resorption, but this option excludes the more commonly used term Howship's lacunae - Since both terms describe identical structures, this answer is **incomplete** *Neither Howship's lacunae nor resorption bays.* - This is **completely incorrect** - both terms specifically describe the anatomical sites where osteoclasts perform bone resorption - These lacunae/bays are the **definitive histological markers** of osteoclastic activity and bone remodeling **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1182-1184.

Q: MIC-2 (CD99) expression is most characteristically associated with

Ewings sarcoma. ***Ewings sarcoma*** - **MIC-2 (CD99)** is a highly sensitive and widely used immunohistochemical marker for **Ewing sarcoma** [2]. - Its expression is observed in nearly **95%** of Ewing sarcoma cases, reflecting the characteristic neuroectodermal differentiation of this tumor. *Alveolar soft tissue sarcoma* - This tumor typically expresses **TFE3**, a transcription factor involved in its unique genomic translocation, and is generally **negative for CD99**. - It is characterized by a distinctive **alveolar growth pattern** and granular eosinophilic cytoplasm, differentiating it from Ewing sarcoma. *Osteosarcoma* - Osteosarcomas are primarily characterized by the production of **osteoid** by malignant cells and are typically **negative for CD99** [1]. - Immunohistochemical markers for osteosarcoma often include **alkaline phosphatase** and osteocalcin. *Dermatofibrosarcoma protuberans* - This tumor is characterized by expression of **CD34** and a specific **COL1A1-PDGFB fusion gene**. - It is typically **negative for CD99**, which helps differentiate it from other spindle cell tumors. **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. 671-672.

Q: Not a true statement about Osteoclastoma

Originates in the metaphyseal region of bones. ***Originates in the metaphyseal region of bones*** - Giant cell tumors (**osteoclastoma**) are typically found in the **epiphyseal region** of long bones, particularly around the knee (distal femur and proximal tibia), rather than the metaphysis [1]. - While they can extend into the metaphysis, their origin is characteristically **epiphyseal** after skeletal maturity [1]. *Benign bone tumor* - **Giant cell tumors** are considered **benign but locally aggressive** tumors [1]. - They have a potential for **local recurrence** and, rarely, **malignant transformation** or distant metastasis (typically to the lungs). *Usually solitary* - **Giant cell tumors** are almost always **solitary lesions** [1]. - Multifocal involvement is exceedingly rare and should prompt investigation for underlying syndromes or alternative diagnoses. *Common in age between 20-40 years* - Giant cell tumors typically occur in skeletally mature individuals, with a peak incidence in the **third and fourth decades of life** (20-40 years old). - They are rare before skeletal maturity because the epiphysis has not yet fused. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1205-1206.

Q: Muscle biopsy shows ragged red fibers on modified Gomori trichrome stain. Which enzyme defect is most likely?

Complex I. ***Complex I*** - **Ragged red fibers** on modified Gomori trichrome stain are the pathological hallmark of **mitochondrial myopathies** [1] - **Complex I (NADH-CoQ reductase) deficiency** is the **most common cause** of mitochondrial disease, accounting for approximately 30-40% of all cases - Complex I deficiency is the **most frequent cause of ragged red fibers** in muscle biopsies - Associated clinical features include progressive muscle weakness, exercise intolerance, lactic acidosis, and encephalomyopathy (Leigh syndrome) [1] - The ragged red appearance results from subsarcolemmal accumulation of abnormal mitochondria attempting to compensate for defective oxidative phosphorylation *Complex II* - **Complex II (succinate dehydrogenase) deficiency** is a relatively rare cause of mitochondrial myopathy - More commonly associated with hereditary paraganglioma-pheochromocytoma syndromes and certain cancers - Can cause ragged red fibers but is much less common than Complex I deficiency - The only complex entirely encoded by nuclear DNA (not mitochondrial DNA) *Complex III* - **Complex III (ubiquinol-cytochrome c reductase) deficiency** is a rare cause of mitochondrial disease - Can present with myopathy and ragged red fibers, but accounts for only a small percentage of mitochondrial disorders - Associated with exercise intolerance and multisystem involvement when present *Complex IV* - **Complex IV (cytochrome c oxidase, COX) deficiency** can cause mitochondrial myopathy with ragged red fibers [1] - However, it is **less common than Complex I deficiency** as a cause of ragged red fibers - COX-deficient fibers can be identified using specific COX histochemical staining [1] - Associated with Leigh syndrome and other encephalomyopathies, but not the **most likely** cause when ragged red fibers are present **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1305-1306.

Q: A patient with multiple fractures and blue sclerae is suspected of having osteogenesis imperfecta. What genetic mutation is most commonly associated with this condition?

COL1A1. ***COL1A1*** - **Osteogenesis imperfecta** is primarily caused by mutations in the genes encoding **Type I collagen**, specifically **COL1A1** and **COL1A2**. - Mutations in **COL1A1** account for the **majority of cases** (~60-70%), with COL1A2 mutations responsible for most remaining cases, and lead to defective collagen synthesis or structure, resulting in brittle bones and other connective tissue abnormalities like **blue sclerae** [1]. - The defective collagen weakens bone matrix, leading to the characteristic **multiple fractures** with minimal trauma [2]. *BRCA1* - **BRCA1** is a tumor suppressor gene associated with an increased risk of developing **breast cancer** and **ovarian cancer**. - Mutations in **BRCA1** play no role in the pathogenesis of osteogenesis imperfecta or collagen synthesis. *RB1* - **RB1** is a tumor suppressor gene linked to **retinoblastoma**, a rare childhood eye cancer, and other malignancies. - Mutations in **RB1** are not involved in collagen synthesis or bone formation. *P53* - **P53** is a critical tumor suppressor gene often termed the "guardian of the genome," playing a role in cell cycle arrest, apoptosis, and DNA repair. - While fundamental in cancer biology, mutations in **P53** are not associated with osteogenesis imperfecta. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 671-672. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, p. 1188.

Q: A young patient is diagnosed with osteosarcoma. Which region of the long bones is most commonly affected?

Metaphysis. ***Correct: Metaphysis*** - The **metaphysis** is the most common site for osteosarcoma development due to its rich vascular supply and high rate of osteoblastic activity during bone growth. - This region is actively growing and undergoing rapid cell division, making it more susceptible to malignant transformation. - Osteosarcoma most commonly affects the metaphyseal region around the knee (distal femur and proximal tibia). *Incorrect: Epiphysis* - The **epiphysis** is the end part of a long bone, initially separated from the main bone by cartilage but later fused with it. - While other tumors like **chondroblastoma** and **giant cell tumor** can occur here, osteosarcoma is rarely found in this region. *Incorrect: Diaphysis* - The **diaphysis** is the main shaft of a long bone, consisting of compact bone. - While other bone tumors like **Ewing sarcoma** commonly affect the diaphysis, osteosarcoma is less frequent in this area compared to the metaphysis. *Incorrect: Articular surface* - The **articular surface** is covered with cartilage and is involved in joint articulation. - Tumors rarely originate directly from the articular cartilage or surface, and osteosarcoma has no predilection for this region.

Q: Most common age group affected by Osteosarcoma

10-20 years. ***10-20 years*** [1] - **Osteosarcoma** is the most common primary malignant bone tumor and has a bimodal age distribution, with peaks in **adolescence (10-20 years)** coinciding with rapid growth and secondarily in older adults [1]. - The peak incidence in adolescents is attributed to the increased osteoblastic activity during **pubertal growth spurts**, making these cells more susceptible to malignant transformation. *Up to 10 years* - While pediatric bone tumors can occur, osteosarcoma is **less common** in children under 10 compared to the adolescent age group. - Other bone tumors like **Ewing sarcoma** might be more prevalent in this younger age range, especially in early childhood [2]. *30-40 years* - This age group is generally **less affected** by primary osteosarcoma compared to adolescents and older adults. - The incidence significantly decreases after the adolescent peak and before the secondary peak in older adults. *Older than 45 years* - A secondary peak of osteosarcoma occurs in older adults, often associated with **Paget's disease of bone** or previous **radiation exposure** [1]. - However, the most prominent and common age group for osteosarcoma overall is still adolescents. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1198-1200. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 671-672.

Q: Which condition characterized by multiple enchondromas AND hemangiomas is associated with an increased risk of developing chondrosarcomas?

Maffucci syndrome. ***Maffucci syndrome*** - **Maffucci syndrome** is a rare, non-hereditary disorder characterized by the presence of multiple **enchondromas** (benign cartilaginous tumors) AND **hemangiomas** (benign vascular tumors) - The combination of enchondromas with vascular lesions is diagnostic of Maffucci syndrome - A significant complication is malignant transformation of enchondromas into **chondrosarcomas**, with a risk of approximately **15-30%** - The presence of hemangiomas differentiates it from Ollier disease *Felty syndrome* - **Felty syndrome** is a complication of **rheumatoid arthritis**, characterized by the triad of rheumatoid arthritis, **splenomegaly**, and **neutropenia** - Not associated with enchondromas, hemangiomas, or chondrosarcomas - Its primary effects relate to immune dysfunction and increased infection susceptibility *Ollier disease* - **Ollier disease** is characterized by multiple **enchondromas** but WITHOUT hemangiomas (this is the key differentiating feature) - Also carries increased risk of chondrosarcoma transformation (25-50%), actually higher than Maffucci syndrome - Typically shows unilateral distribution - The absence of vascular lesions distinguishes it from Maffucci syndrome *None of the options* - Incorrect because **Maffucci syndrome** fits the description of having both enchondromas AND hemangiomas with chondrosarcoma risk

Q: What is the most common site of metastasis in the skeleton?

Vertebrae. ***Vertebrae*** - The **vertebrae** are the most common sites of metastasis in the skeleton due to their **high blood supply** and involvement in various malignancies [1]. - This frequently leads to conditions such as **vertebral compression fractures** and is associated with significant **back pain** and neurological deficits [1]. *Skull* - While the **skull** can be involved, it is not the most frequent site for skeletal metastases, with the vertebrae being more common [1]. - Metastasis to the skull may present as **local pain** or **swelling**, but overall, it is less prevalent compared to vertebral involvement. *Femur* - The **femur** can be a site for metastasis, particularly in certain cancers, but it is less common than the vertebrae [2]. - Metastatic lesions in the femur are more often associated with **pathologic fractures** rather than being the primary site of metastasis [1]. *Tibia* - The **tibia** is also a possible site of metastatic spread, but this is rare compared to the vertebrae [2]. - Typically associated with **painful lesions**, the tibia's involvement often indicates advanced disease but is not a primary site like the vertebrae. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 674-675. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 671-672.

Question 1

A 10-year-old child with known hemophilia presents with ankle pain. X-ray shows a lytic lesion with sclerotic rim at the calcaneum. What is the most likely diagnosis?

Accepted Answer

Pseudotumor associated with bleeding disorders

Answer

Ochronosis

Answer

PVNS

Answer

Eumycosis

Question 2

At which of the following sites do osteoclasts remove bone?

Accepted Answer

Both Howship's lacunae and resorption bays.

Answer

Howship's lacunae

Answer

Resorption bays

Answer

Neither Howship's lacunae nor resorption bays.

Question 3

MIC-2 (CD99) expression is most characteristically associated with

Accepted Answer

Ewings sarcoma

Answer

Alveolar soft tissue sarcoma

Answer

Osteosarcoma

Answer

Dermatofibrosarcoma protuberans

Question 4

Not a true statement about Osteoclastoma

Accepted Answer

Originates in the metaphyseal region of bones

Answer

Benign bone tumor

Answer

Usually solitary

Answer

Common in age between 20-40 years

Question 5

Muscle biopsy shows ragged red fibers on modified Gomori trichrome stain. Which enzyme defect is most likely?

Accepted Answer

Complex I

Answer

Complex IV

Answer

Complex II

Answer

Complex III

Question 6

A patient with multiple fractures and blue sclerae is suspected of having osteogenesis imperfecta. What genetic mutation is most commonly associated with this condition?

Accepted Answer

COL1A1

Answer

BRCA1

Answer

RB1

Answer

P53

Question 7

A young patient is diagnosed with osteosarcoma. Which region of the long bones is most commonly affected?

Accepted Answer

Metaphysis

Answer

Epiphysis

Answer

Diaphysis

Answer

Articular surface

Question 8

Most common age group affected by Osteosarcoma

Accepted Answer

10-20 years

Answer

Up to 10 years

Answer

Older than 45 years

Answer

30-40 years

Question 9

Which condition characterized by multiple enchondromas AND hemangiomas is associated with an increased risk of developing chondrosarcomas?

Accepted Answer

Maffucci syndrome

Answer

None of the options

Answer

Felty syndrome

Answer

Ollier disease

Question 10

What is the most common site of metastasis in the skeleton?

Accepted Answer

Vertebrae

Answer

Femur

Answer

Tibia

Answer

Skull

Bone and Soft Tissue Pathology — MCQs

Bone and Soft Tissue Pathology — MCQs

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