Gamma Knife Radiosurgery and Immunotherapy as Primary Treatment for a Malignant Tumor of the Cranial Base beginning as Lentigo Maligna: A Case Report.

Melanoma in the head and neck is known to metastasize to cranial nerves. Prompt treatment is critical for preventing progression and reducing neuropathy. We report a patient who presented with cranial neuropathy related to a malignant skull base lesion that originated as lentigo maligna. The diagnosis was challenging, requiring two surgeries to obtain tissue and neither biopsy leading to a definitive diagnosis. Pathological analyses demonstrated positive immunoreactivity for SOX10 and S100, preservation of H3K27me3, and PTEN and STK11 mutations. The patient was managed with Gamma Knife Radiosurgery and combination immunotherapy. Imaging at 9 months post-SRS showed resolution of the mass lesion. Clinically, the patient has occasional left-sided facial pain requiring no medication and denies facial numbness. We favor a diagnosis of desmoplastic neurotropic melanoma due to the neurotropic spread and response to melanoma-targeted immunotherapy.