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Perineuriomas are rare WHO grade 1 tumors composed of neoplastic perineural cells. They are found either in the deep soft tissues or arising from peripheral nerves of the limbs or rarely the cranial nerves.
The epidemiology of perineuriomas depends on their locations.
Soft tissue perineuriomas occur in adults and are more frequent in females (M:F 1:2)1.
Intraneural perineuriomas are encountered in young adults and adolescents with no sex predilection 1,2.
Typically patients with intraneural perineuriomas present with muscle weakness 1. Soft tissue perineuriomas present as deep masses, or in cases of malignant degeneration, metastatic disease, or direct invasion, although this is uncommon 1.
Perineuriomas can be divided according to their location and relationship to larger nerves.
When they arise in deep soft tissues, referred to as soft tissue perineurioma or extraneural perineurioma they are unassociated with sizable identifiable nerves.
Instead, when they arise from peripheral nerves of the limbs or rarely the cranial nerves, they are known as intraneural perineuriomas 1.
Perineuriomas are indolent low-grade tumors (WHO grade 1) 1.
Very rarely tumors with similar morphology but high-grade features are encountered, previously known as malignant perineuiomas. These are now considered variants of malignant peripheral nerve sheath tumors (MPNST) and are also known as MPNST with perineural differentiation 1.
Soft tissue perineuriomas appear as well-circumscribed rounded masses 1.
Intraneural perineuriomas present as a fusiform expansion of a segment of peripheral nerve, ranging greatly in length, but typically longer than 10 cm 1,2. Multiple nerve fascicles are involved and enlarged but do not demonstrate the bag-of-worms appearance seen in plexiform neurofibromas 1.
Perineuriomas are composed of neoplastic perineural cells, the disposition of which varies with the location of the tumors.
Soft tissue perineuriomas demonstrate a whorled or storiform arrangement of neoplastic cells, within a collagen background 1.
Intraneural perineuriomas demonstrate extension of neoplastic perineural cells around axons, largely contained by the endoneurium 1.
Intraneural perineuriomas appear as fusiform enlargement of a nerve with increased T2 signal and contrast enhancement 2.
Treatment and prognosis
Soft tissue perineuriomas can usually be cured with resection, although local recurrence and metastasis are described in malignant tumors 1.
Intraneural perineuriomas can be treated conservatively following histological confirmation with biopsy 1. Alternatively, the mass can be resected with or without nerve grafting 2.
The differential diagnosis for intraneural perineuriomas includes 2: