Calvarial multiple myeloma: Raindrop skull

The "Raindrop skull" appearance represents the multiple punched-out and lytic lesions hitting a surface and creating a scattered splash pattern.

A 73-year-old female presented with multiple painless lumps over the forehead and head. The patient reported unintentional weight loss, fatigability, loss of appetite, fever, night sweats, and back pain for seven months (B symptoms). The examination revealed multiple, nonmobile, calvarial lesions with defined borders, measuring approximately 1 × 1 cm. Laboratory investigations of serum-free light chains showed a free kappa level of 12.91 mg/L, a lambda level of 4549.28 mg/L, and a free kappa/lambda ratio of 0.00. Radiological imaging of the skull and brain showed a "raindrop skull" appearance and multiple calvarial osteolytic lesions. The patient underwent a right superior iliac crest bone marrow aspirate and trephine biopsy. The laboratory and histopathological sections were compatible with multiple myeloma. A diagnosis of multiple myeloma (free light chain lambda) was rendered.

Calvarial multiple myeloma is rare and requires a high index of suspicion to diagnose. "Raindrop skull" appearance is pathognomonic of calvarial multiple myeloma.