Brain metastatic carcinoma is a rare occurrence among prostate cancer metastases. 68Gallium prostate-specific membrane antigen PET-CT ([68Ga]PSMA PET/CT) is commonly used for prostate cancer staging and detection of biochemical recurrences. However, various CNS tumors exhibit activity on [68Ga]PSMA PET/CT and may often be included in the differential diagnosis. Herein, we present a case of brain metastatic prostate cancer successfully treated with surgical resection and adjuvant stereotactic Gamma Knife radiosurgery (GKRS) followed by androgen deprivation therapy (ADT) to emphasize the need for histologic confirmation. A 70-year-old male with a history of very high-risk prostatic adenocarcinoma presented with biochemical recurrence following radical prostatectomy and irradiation of the prostatic fossa. [68Ga]PSMA PET/CT and MRI identified a solitary lesion in the left occipital lobe; differential diagnosis included prostate metastasis, meningioma, or a new metastatic primary lesion. The patient underwent surgical resection, and immunohistochemical staining confirmed the lesion as brain metastatic prostate adenocarcinoma. One month after resection, the patient underwent GKRS to the tumor bed and two additional metastases, followed by ADT. Repeated imaging 15 months after GKRS revealed stable posttreatment changes with no evidence of new metastases, thus demonstrating durable, effective local and systemic control. Brain metastatic prostate adenocarcinoma without nodal or osseous metastases is a rare phenomenon. The affinity of [68Ga]PSMA PET/CT for non-prostate histologies such as meningioma introduces uncertainty into the diagnostic process. This case demonstrates the durable local control conferred by GKRS toward these lesions and emphasizes the need for clinical, radiographic, and histopathologic data to identify disease presentations and facilitate appropriate treatment regimens.

Central nervous system (CNS) metastases of atypical carcinoid tumors are exceptionally rare. Isolated studies suggest a survival benefit in patients who receive whole-brain radiotherapy (WBRT); however, it has been known to have detrimental effects on long-term memory and executive function. Here, we present a case of a patient initially diagnosed with stage IIB bronchopulmonary carcinoid who later developed hepatic and intracranial metastases despite receiving adjuvant systemic therapy over a two-year period. She underwent hippocampal-sparing WBRT (HS-WBRT), receiving 30 Gy in 10 fractions via daily image-guided photon therapy using two coplanar arcs. Subsequent clinical evaluations and magnetic resonance imaging (MRI) of the brain at 11 months post-treatment demonstrated a decrease in the size and number of brain metastases, with the patient reporting stable memory and cognition. This case demonstrates the efficacious delivery of palliative HS-WBRT in a patient with a rare presentation of brain-metastatic atypical carcinoid, conferring effective local control and preservation of cognition. Multi-therapy regimens that incorporate HS-WBRT may be considered for improved disease control and quality of life. Further investigation of systemic agents, and possible molecular targets that could confer greater efficacy against treatment-progressive atypical carcinoids, is also warranted.