A 3-year-old boy presents with a painless lump over the left parietal scalp and polyuria with polydipsia of 2 months duration. Serum sodium is 152 mEq/L with dilute urine. Skull radiograph shows a sharply punched-out lytic lesion with a beveled edge. Biopsy shows cells positive for CD1a and S100 with Birbeck granules on electron microscopy. What is the diagnosis?

• A Ewing sarcoma with ectopic ADH secretion
• B Langerhans cell histiocytosis with diabetes insipidus ✓
• C Juvenile xanthogranuloma with nephrogenic diabetes insipidus
• D Neuroblastoma metastatic to skull with SIADH

Explanation

Lytic skull lesions with a beveled margin, pituitary stalk involvement causing central diabetes insipidus, and CD1a positive, Birbeck granule containing histiocytes define Langerhans cell histiocytosis. The combination of lytic bone lesions, exophthalmos, and diabetes insipidus forms the classic Hand-Schuller-Christian triad. Ewing sarcoma does not produce Birbeck granules or cause DI, and neuroblastoma metastases are associated with raised catecholamines rather than this immunophenotype.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.