# Distinct Imaging Features of Peripheral Nerve Sheath Tumours in NF2-Related Schwannomatosis: A Case Report

## TL;DR

A teenage patient with NF2-related schwannomatosis showed unusual nerve imaging features not typical of classic schwannomas.

## Contribution

The case highlights distinct imaging features of perineurioma in NF2-related schwannomatosis, rarely reported before.

## Key findings

- Ultrasound showed fusiform, multifascicular enlargement of the ulnar nerve and brachial plexus.
- MRI revealed T2-hyperintense and T1-isointense nerve changes with diffuse gadolinium enhancement.
- The findings suggest perineurioma as a rare but possible manifestation in NF2-related schwannomatosis.

## Abstract

Peripheral nerve sheath tumours (PNST) are an important feature of the NF2-related schwannomatosis. These constitute primarily schwannomas which are characterized as nodular, solitary benign tumours of single fascicles. We here describe a pronounced, extensive, multifascicular enlargement of the right ulnar nerve and bilateral brachial plexus in a teenage patient with NF2-related schwannomatosis. Neither their imaging nor the clinical characterization were consistent with classic schwannomas.

Within a multimodal work-up, detailed and standardized high-resolution nerve ultrasound was correlated to clinical, electroneurographic, and MRI findings. Follow-up data over 2 years were provided.

The clinical presentation of a slowly progressive, predominantly motor axonal neuropathy of the right ulnar nerve prompted a comprehensive nerve ultrasound examination, initiated by this clinically and neurophysiologically defined “sentinel” finding. Ultrasound imaging revealed an extensive, fusiform enlargement of the right ulnar nerve, as well as bilateral involvement of the brachial plexus, the latter without corresponding clinical symptoms. Subsequent genetic analysis confirmed the diagnosis of NF2-related schwannomatosis.

Signs of a mononeuropathy are a frequent manifestation of NF2-related schwannomatosis in childhood. The here presented nerve imaging characteristics, however, did not correspond to classic schwannomas. The fusiform, long-extended, multifascicular enlargement with mixed hyper- and hypoechogenic components on ultrasound, as well as markedly T2-hyperintense and T1-isointense appearance with diffuse gadolinium enhancement on MRI, is consistent with perineurioma. These mesenchymal nerve tumours have rarely been described in NF2-related schwannomatosis. This association is further supported by the present case and highlights the necessity for additional peripheral nerve imaging studies in NF2-related schwannomatosis, including the application of high-resolution ultrasound.