Schwannomas of the deep motor branch of the ulnar nerve: a systematic review of the literature with an additional case report and anatomical analysis.

[PURPOSE] Schwannomas originating from the deep motor branch of the ulnar nerve (DMBUN) are exceptionally rare, presenting with variable and often heterogeneous clinical manifestations depending on their precise anatomical location. While these tumors have been described in the literature, reports specifically involving the DMBUN are exceedingly limited, rendering postoperative prognostication challenging. This study aims to systematically review the existing literature and present a novel case, with the objective of delineating anatomical characteristics and clarifying potential postoperative outcomes.

[METHODS] A systematic literature search was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, using the MEDLINE and Scopus databases. Data regarding patient demographics, clinical presentation, anatomical localization, and surgical outcomes were extracted and analyzed.

[RESULTS] Seven articles met the inclusion criteria. A total of nine tumors were initially identified as schwannomas of the DMBUN over a 73-year period; however, only five cases - including the newly reported one - were confirmed. The median patient age was 59.6 years; complete recovery was achieved in three cases, with time to functional improvement ranging from 4 to 6 months.

[CONCLUSION] In this limited series, available data suggest that accurate preoperative imaging and careful intraoperative microsurgical dissection may lead to favorable outcomes, with complete recovery achievable in schwannomas of the DMBUN. No clear association was observed between postoperative nerve function and tumor size, patient age, or time since symptom onset.