Optimal management of brainstem metastases: a narrative review

Background and Objective: Brainstem metastases comprise fewer than 7% of all brain metastases. Nonetheless, they present clinicians with unique clinical challenges in symptom management and treatment. No comprehensive review summarizing the management of brainstem metastases exists. This review aims to summarize epidemiology, anatomy, clinical correlation, prognosis, options for management of symptoms, treatment, treatment toxicity, and dose and fractionation for brainstem stereotactic radiosurgery (SRS) as reported in the literature. Methods: In July 2021, we searched PubMed and Embase for retrospective studies of brainstem metastasis treatment, as well as case series and case reports describing diagnosis and clinical management of brainstem metastasis. Keywords and MeSH terms searched included “brainstem metastasis”, “symptomatic brainstem metastasis”, “brain metastasis”, “stereotactic radiosurgery brainstem”, “whole brain radiation brainstem”, “brainstem metastasis resection”, “brainstem radiation toxicity”, “brainstem radiosurgery toxicity”, “brainstem radiosurgery dose”, and “radiosurgery dose tolerance”. Titles and abstracts were screened for relevant articles and studies. References from full-text articles were screened for additional studies. Key Content and Findings: Single-institution studies and multicenter retrospective analyses from 1993 to 2021 reflect a shift from reliance on whole-brain radiation therapy (WBRT) to SRS for primary treatment of brainstem metastases. Recent multicenter retrospective analyses and single-institution case series support the safety and efficacy of SRS of brainstem metastases in symptom management and preservation of quality of life. Incidence of radiation-induced toxicity following SRS of brainstem metastases is comparable to that of SRS for other brain metastases. Complications following brainstem SRS are most strongly associated with prior WBRT. Conclusions: Radiation oncologists play a central role in the treatment of brainstem metastases due to reliance on SRS. Dose and fractionation of brainstem SRS remain largely institution-dependent. The field would benefit from inclusion of brainstem metastases in prospective trials of SRS and studies of adverse effects of salvage WBRT after prior SRS of brainstem metastases.