Multiple myeloma with pathologically proven skull plasmacytoma after a mild head injury: Case report.

Rationale: MM is a malignant tumor originating from the plasma cells of the bone marrow. Central nervous system myelomatosis is very rare and may be a complication of MM.

Patient Concerns: A 60-year-old man presented with a slowly growing soft mass at his right frontal scalp after a mild head injury 6 months ago.

Diagnoses: Neuroradiological examinations revealed a solid intracranial-extracranial mass with an osteolytic lesion in the skull. Histopathological examination showed skull plasmacytoma, and postoperative examinations revealed multiple myeloma.

Interventions: The tumor was completely removed and the skull defect repaired with the titanium mesh. Then, chemotherapy was initiated after surgery with bortezomib and dexamethasone.

Outcomes: The patient received eight chemotherapies within one year after surgery.

Lessons: Despite a history of head injury, a differential diagnosis should be kept in mind during the diagnosis of solid intracranial-extracranial masses, especially in the presence of osteolytic skull at the lesioned site.