Bone and Soft Tissue Pathology Practice Questions

Q: A 14 year old male presents with mushroom like tumor in the distal femur for past 2 years. Which of the following features suggest malignant transformation?

Cartilage thickness $>2 \mathrm{~cm}$. ***Cartilage thickness >2 cm*** - A **cartilage cap thickness greater than 2 cm** in an osteochondroma in an adult (or >3 cm in children) is a strong indicator of **malignant transformation** into a secondary peripheral **chondrosarcoma**. [2], [3] - **Key imaging finding:** Cartilage cap measured on MRI or CT scan - Other features suggesting malignant transformation include continued growth after skeletal maturity, new or increasing pain, cortical destruction, and new soft tissue mass. [2], [3] *Presence of cartilage cap* - All osteochondromas have a cartilage cap by definition - this is a normal feature, not a sign of malignancy. [1] - The **thickness** of the cap, not its presence, is what matters. *Location in metaphysis* - Osteochondromas typically arise from the metaphysis near the growth plate - this is a normal location. [3] - Location alone does not indicate malignant transformation. *Size less than 1 cm* - Small size suggests a benign, stable lesion. - Malignant transformation is suggested by **increasing size** and growth after skeletal maturity, not small size. [2] **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, p. 1202. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 672-673. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1202-1204.

Q: A muscle biopsy shows 'moth-eaten' fibers. Which histochemical finding would confirm mitochondrial myopathy?

Ragged red fibers on MGT. ***Ragged red fibers on MGT*** - The presence of **ragged red fibers** on a **modified Gomori trichrome (MGT) stain** is the histological hallmark of **mitochondrial myopathies**. - These fibers represent abnormal accumulation of **dysfunctional mitochondria** beneath the sarcolemma. *Type 1 fiber predominance* - While some myopathies may show type 1 fiber predominance, it is a **non-specific finding** and does not confirm mitochondrial myopathy. - It can be seen in various conditions, including **neurogenic atrophy** or some **congenital myopathies**. *Rimmed vacuoles* - **Rimmed vacuoles** are characteristic of **inclusion body myositis** (IBM) and some **distal myopathies**. - They are not a specific finding for mitochondrial myopathy. *Nemaline rods* - **Nemaline rods** are pathognomonic for **nemaline rod myopathy**, a distinct form of congenital myopathy. - They are composed of **actin filament aggregates** and are unrelated to mitochondrial dysfunction.

Q: Most common type of lesion in Pott's spine:

Paradiscal. ***Paradiscal*** - **Paradiscal lesions** are the most characteristic and common type of lesion in Pott's spine (approximately 50% of cases), preferentially affecting the anterior vertebral body adjacent to the intervertebral disc [1]. - This location is rich in **vascularity**, allowing Mycobacterium tuberculosis to spread more easily and cause significant destruction of the vertebral bodies and discs [1]. - Typically results in **angular kyphosis (gibbus deformity)** due to anterior vertebral collapse. *Posterior* - **Posterior lesions** affect the posterior elements of the vertebrae including the pedicles, laminae, and spinous processes. - This is the **rarest type** of tuberculous spinal involvement. - May present with neurological deficits due to posterior encroachment on the spinal canal. *Central* - A **central lesion** in Pott's spine involves primarily the vertebral body itself, without specific early involvement of the disc space or adjacent vertebrae. - This type is less common than paradiscal lesions and typically leads to **vertebra plana** (flat vertebra) or uniform **compression fracture** rather than angular kyphosis. *Anterior* - **Anterior lesions** affect the front part of the vertebral body and can lead to a wedge-shaped collapse. - While the anterior column is frequently involved, the term "anterior" is less specific than "paradiscal" in describing the most common initial location that characteristically spreads to the intervertebral disc space. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1197-1198.

Q: Albers-Schönberg disease is:

Osteopetrosis. ***Osteopetrosis*** - **Albers-Schönberg disease** is another name for **osteopetrosis**, also known as **marble bone disease** [1]. - It is a group of rare genetic disorders characterized by abnormally **dense bones** due to a defect in **osteoclast** function, leading to impaired bone resorption [1]. *Osteoporosis* - **Osteoporosis** is characterized by decreased bone density and structural deterioration of bone tissue, leading to an increased risk of fractures. - It results from an imbalance where **bone resorption outpaces bone formation**, the opposite of osteopetrosis. *Paget* (Paget's disease of bone) - **Paget's disease of bone** involves localized areas of increased bone turnover, leading to disorganized bone remodeling and weakened, enlarged bones. - It is distinct from osteopetrosis, which involves a generalized increase in bone density. *Osteogenesis imperfecta* - **Osteogenesis imperfecta** (OI), or brittle bone disease, is a genetic disorder causing extremely fragile bones prone to fractures, often due to defects in **collagen production** [1]. - This condition presents with bone fragility and often blue sclera, which is the opposite of the increased bone density seen in osteopetrosis. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1188-1189.

Q: Marble bone disease is:

Osteopetrosis. ***Osteopetrosis*** - **Osteopetrosis**, also known as **marble bone disease**, is a rare genetic disorder characterized by abnormally dense bones due to a defect in **osteoclast function** [1]. - Impaired bone resorption leads to an accumulation of woven bone, causing bones to be fragile despite their density [1]. *Osteosclerosis* - **Osteosclerosis** is a general term for increased bone density and can be a feature of various conditions, including osteopetrosis. - However, it is a descriptive term rather than a specific disease diagnosis equivalent to marble bone disease. *Histiocytosis X* - **Histiocytosis X**, also known as **Langerhans cell histiocytosis**, is a rare disorder involving the proliferation of Langerhans cells. - It primarily affects bone but can also involve other organs, presenting with lytic lesions rather than increased bone density. *Osteomalacia* - **Osteomalacia** is a condition characterized by inadequate mineralization of bone tissue, leading to soft and weakened bones. - It is typically caused by **vitamin D deficiency** and is the opposite of increased bone density. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1188-1189.

Q: Crystals deposited in Pseudogout:

Calcium pyrophosphate dihydrate. ***Calcium pyrophosphate dihydrate*** - **Calcium pyrophosphate dihydrate (CPPD)** crystals are characteristic of pseudogout, also known as **CPPD deposition disease**. [1] - These crystals typically appear **rhomboid-shaped** and show **positive birefringence** under polarized light microscopy. [1] *Calcium oxalate* - **Calcium oxalate** crystals are primarily associated with **kidney stones** and severe kidney disease. - They are not the causative agent for pseudogout, which involves different crystal types and joint pathology. *Monosodium urate* - **Monosodium urate** is the crystal form associated with **gout**, forming needle-shaped crystals with **negative birefringence**. [2] - This is distinct from pseudogout, which involves CPPD crystals and a different clinical presentation. [1], [2] *Amyloid* - **Amyloid** refers to insoluble, misfolded proteins that can deposit in various tissues and organs, causing **amyloidosis**. - Amyloid deposits are associated with organ dysfunction but do not form the characteristic crystals found in pseudogout. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Osteoarticular And Connective Tissue Disease, pp. 683-684. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, pp. 1218-1220.

Q: Osteogenesis imperfecta is due to

Defective synthesis of type I collagen. ***Defective synthesis of type I collagen*** - **Osteogenesis imperfecta** is primarily caused by mutations in genes (COL1A1 or COL1A2) that encode **Type I collagen**, leading to defective collagen synthesis [1]. - This defective collagen results in **fragile bones**, leading to recurrent fractures, which is the hallmark of the disorder [1]. *Inborn error of the methionine metabolism* - An inborn error of methionine metabolism, such as **homocystinuria**, affects multiple systems including bone, but it causes **osteoporosis** and marfanoid habitus, not the typical features of osteogenesis imperfecta. - Homocystinuria is characterized by **thromboembolism**, **ectopia lentis**, and developmental delay, which are not features of osteogenesis imperfecta. *Growth hormone dysfunction* - **Growth hormone dysfunction** primarily leads to growth disturbances like **dwarfism** or **gigantism**, but does not directly cause the characteristic bone fragility and connective tissue defects seen in osteogenesis imperfecta. - While growth hormone can influence bone metabolism, its dysfunction is not the underlying genetic defect responsible for osteogenesis imperfecta. *Bony abnormality confined to the metaphysis* - A bony abnormality confined to the **metaphysis** is characteristic of conditions like **rickets** or **achondroplasia**, where there are issues with cartilage growth and ossification. - **Osteogenesis imperfecta** affects the entire bone structure due to a systemic defect in collagen, not just a confined region like the metaphysis. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Bones, Joints, and Soft Tissue Tumors, p. 1188.

Question 1

A 14 year old male presents with mushroom like tumor in the distal femur for past 2 years. Which of the following features suggest malignant transformation?

Accepted Answer

Cartilage thickness $>2 \mathrm{~cm}$

Answer

Presence of cartilage cap

Answer

Location in metaphysis

Answer

Size less than 1 cm

Question 2

A 5 year old child who presented with proptosis of one of the eyes was found to have a desmin positive tumour. What is the probable diagnosis?

Accepted Answer

Rhabdomyosarcoma

Answer

Neuroblastoma

Answer

Retinoblastoma

Answer

Ewing's sarcoma

Question 3

A 12-year-old Caucasian male presents with his mother to the pediatrician’s office complaining of right thigh pain. He reports that he has noticed slowly progressive pain and swelling over the distal aspect of his right thigh over the past two months. He denies any recent trauma to the area and his temperature is 100.9°F (38.3°C). On exam, there is swelling and tenderness overlying the distal right femoral diaphysis. Laboratory evaluation is notable for an elevated white blood cell (WBC) count and elevated erythrocyte sedimentation rate (ESR). A radiograph of the patient’s right leg is shown. Biopsy of the lesion demonstrates sheets of monotonous small round blue cells with minimal cytoplasm. Which of the following genetic mutations is most likely associated with this patient’s condition?

Accepted Answer

t(11;22)

Answer

RB1 inactivation

Answer

TP53 inactivation

Answer

t(8;14)

Answer

t(X;18)

Question 4

A muscle biopsy shows 'moth-eaten' fibers. Which histochemical finding would confirm mitochondrial myopathy?

Accepted Answer

Ragged red fibers on MGT

Answer

Type 1 fiber predominance

Answer

Rimmed vacuoles

Answer

Nemaline rods

Question 5

Most common type of lesion in Pott's spine:

Accepted Answer

Paradiscal

Answer

Posterior

Answer

Central

Answer

Question 6

Albers-Schönberg disease is:

Accepted Answer

Osteopetrosis

Answer

Osteoporosis

Answer

Paget

Answer

Osteogenesis imperfecta

Question 7

Marble bone disease is:

Accepted Answer

Osteopetrosis

Answer

Osteosclerosis

Answer

Histiocytosis X

Answer

Osteomalacia

Question 8

Crystals deposited in Pseudogout:

Accepted Answer

Calcium pyrophosphate dihydrate

Answer

Calcium oxalate

Answer

Amyloid

Answer

Monosodium urate

Question 9

Osteogenesis imperfecta is due to

Accepted Answer

Defective synthesis of type I collagen

Answer

Inborn error of the methionine metabolism

Answer

Growth hormone dysfunction

Answer

Bony abnormality confined to the metaphysis

Question 10

The signs of malignant transformation in osteochondroma are all except

Accepted Answer

Weight loss

Answer

Increase in thickness of cartilage cap

Answer

Increase in size

Answer

Pain

Bone and Soft Tissue Pathology — MCQs

Bone and Soft Tissue Pathology — MCQs

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