TOACS FCPS Station · X‑ray Long Bones: Osteopetrosis

📷 X‑ray Long Bones (AP view)

X-ray long bones showing diffuse osteosclerosis and bone-within-bone appearance in osteopetrosis

Figure 1 · AP long bone radiograph · Osteopetrosis – Marble Bone Disease

🔍 Key radiographic features:

✓ Diffuse osteosclerosis – uniformly dense, marble‑like bones
✓ “Bone‑within‑bone” (endobone) – concentric layers of dense bone
✓ Loss of corticomedullary differentiation – no distinct cortex/medullary cavity
✓ Erlenmeyer flask deformity – flared metaphyses (widened)
✓ Brittle bones – may show healing fractures

📋 Clinical scenario (examiner prompt)

A 3‑month‑old infant presents with macrocephaly, hepatosplenomegaly, and pancytopenia. The infant has had hypocalcemic seizures. On examination, there is frontal bossing and vision impairment. A long bone X‑ray (AP view) is shown.

Macrocephaly Endobone Pancytopenia Hypocalcemia

🧑‍⚕️ Examiner tasks · TOACS

1. Identify the diagnosis from the X‑ray and clinical context.

2. Describe the X‑ray findings (diffuse osteosclerosis, endobone, Erlenmeyer flask).

3. Explain the pathophysiology (defective osteoclast bone resorption).

4. Discuss management (HSCT, calcitriol, interferon‑gamma).

⚠️ Key concept: Osteopetrosis (marble bone disease) is caused by defective osteoclast‑mediated bone resorption. The “bone‑within‑bone” (endobone) appearance is a classic radiographic hallmark. Autosomal recessive (infantile malignant) presents in infancy with pancytopenia, hepatosplenomegaly, hypocalcemia, and cranial nerve compression. HSCT is the only curative treatment.

🎯 Expected answers (for examiners)

• Diagnosis: Osteopetrosis (likely autosomal recessive, infantile malignant)
• X‑ray findings: Diffuse osteosclerosis, endobone (bone‑within‑bone), Erlenmeyer flask deformity
• Pathophysiology: Defective osteoclast function → impaired bone resorption → increased bone density but brittle
• Management: HSCT (curative), calcitriol (stimulates osteoclasts), interferon‑gamma (modest benefit), supportive care

⚡ Quick FCPS‑style MCQ

The “bone‑within‑bone” (endobone) appearance on X‑ray is characteristic of:

A. Osteogenesis imperfecta B. Osteopetrosis C. Rickets D. Paget disease

Feature	Osteopetrosis
Pathology	Defective osteoclast function
Bone density	Increased (sclerotic)
Bone quality	Brittle (prone to fractures)
Marrow	Obliterated → pancytopenia
Cranial nerves	Compression → blindness, deafness

🩻 TOACS FCPS Station · X‑ray Long Bones: Osteopetrosis

📷 X‑ray Long Bones (AP view)

🧑‍⚕️ Examiner tasks · TOACS

📌 Topic summary ·