TOACS FCPS Station · X‑ray Forearm: Thrombocytopenia with Absent Radius (TAR Syndrome)

📷 X‑ray Forearm (AP view)

X-ray forearm showing absent radius in TAR syndrome

Figure 1 · AP forearm radiograph · TAR Syndrome – Absent Radius

🔍 Key radiographic features:

✓ Bilateral absence of the radius (radial aplasia)
✓ Shortened, bowed ulna (may be present)
✓ Hand deviated radially (clubhand deformity)
✓ Normal humerus (proximal bone intact)
✓ Bilateral involvement – characteristic of TAR syndrome

📋 Clinical scenario (examiner prompt)

A newborn is noted to have bilateral absence of the radii with short, bowed ulnae and radial deviation of the hands. The infant also has petechiae and bruising on the trunk and extremities. Platelet count is 15,000/μL. An X‑ray of the forearm (AP view) is shown.

Absent radius Thrombocytopenia Bilateral Radial deviation

🧑‍⚕️ Examiner tasks · TOACS

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

2. Describe the X‑ray findings (bilateral radial aplasia, bowed ulna).

3. Explain the pathophysiology (TAR syndrome, megakaryocyte defect).

4. Discuss management (platelet transfusions, orthopedic management).

⚠️ Key concept: TAR syndrome (Thrombocytopenia with Absent Radius) is a rare congenital disorder characterized by bilateral radial aplasia and thrombocytopenia (platelets typically <50,000). Bone marrow shows decreased or absent megakaryocytes. Unlike Fanconi anemia, there is no progressive marrow failure. Thrombocytopenia improves with age (usually by 1-2 years).

🎯 Expected answers (for examiners)

• Diagnosis: TAR syndrome (Thrombocytopenia with Absent Radius)
• X‑ray findings: Bilateral absent radii, short bowed ulnae, radial deviation of hands
• Pathophysiology: Decreased megakaryocyte production in marrow; improves with age
• Management: Platelet transfusions (for bleeding), orthopedic/surgical correction of radial deviation, avoid antiplatelet drugs

⚡ Quick FCPS‑style MCQ

A newborn with bilateral absent radii and thrombocytopenia (platelets 15,000) most likely has:

A. Fanconi anemia B. TAR syndrome C. Wiskott-Aldrich syndrome D. ITP

📌 Topic summary ·

Definition
Thrombocytopenia with absent radius

X‑ray finding
Bilateral radial aplasia

Platelet count
Usually <50,000

Marrow
Decreased/absent megakaryocytes

Prognosis
Improves with age (by 1-2 years)

Treatment
Platelet transfusions, orthopedic correction

Feature	TAR Syndrome	Fanconi Anemia
Radial aplasia	Bilateral	May be unilateral
Thrombocytopenia	Present (improves with age)	Progressive pancytopenia
Marrow	Decreased megakaryocytes	Hypoplastic, progressive
Associated anomalies	Cardiac, GI	Renal, cardiac, microcephaly
Chromosome fragility	No	Yes (diepoxybutane positive)

🩻 TOACS FCPS Station · X‑ray Forearm: Thrombocytopenia with Absent Radius (TAR Syndrome)

📷 X‑ray Forearm (AP view)

🧑‍⚕️ Examiner tasks · TOACS

📌 Topic summary ·