Nearly half of brainstem metastases are asymptomatic upon discovery, in part due to the sensitivity of MRI and its frequent use in workup and follow-up imaging of patients with cancer. Symptomatic brainstem metastases result from direct impingement of nuclei, tracts, or CNs caused by mass effect or vasogenic edema. In a pooled meta-analysis of 22 single-institution studies, Chen and colleagues reported that 49% of brainstem metastases among 1,104 patients were symptomatic at diagnosis, with a 46.8% median incidence of symptomatic brainstem metastasis among the studies. Reports of brainstem-localizing signs in the literature are summarized in Table 2.[8–14] Specifically, involvement of the corticospinal tract can result in hemiparesis while hemisensory loss can result from damage to the medial lemniscus. Ataxia can result from disruption of brainstem-cerebellum communication. CN palsies can be caused by lesions of the CN nuclei, internuclear connections or efferent fibers. Figure 1 demonstrates post-gadolinium MRI imaging of a symptomatic metastatic lesion to the pons.
Axial T1-weighted MRI of pontine metastasis before and after radiosurgery. (A) Melanoma metastatic to the pons resulting in a 6 mm left pontine lesion causing hemiparesis. (B) This lesion was treated with single fraction linear accelerator-based radiosurgery, and 6 months later, the lesion involuted and resolved. MRI, magnetic resonance imaging.
Chin Clin Oncol. 2022;11(2):15 © 2022 AME Publishing Company