Neurilemomma, also known as schwannoma, is a benign, encapsulated neurogenic tumor originating from neural crest derived Schwann cells of any nerve in the body. They present as asymptomatic palpable masses or may induce late neurologic complaints such as chronic neuropathic pain. Diagnosis is usually established 5 years after disease onset.
Neurilemommas are usually located on the flexor surfaces of the limbs (wrist, elbow, knee), and may involve cranial or spinal nerves or even small nerve twigs, causing different types of symptoms . Their peak incidence is between ages 30 and 60 and sex ratio is 1. If a spinal nerve is involved, symptoms mimic disk hernia  .
The tumor itself may cause no pain or it can be tender on palpation. It is usually well defined, slow growing and mobile relative to the underlying and overlying structures. Nerve compression may cause distal paresthesia, carpal tunnel or tarsal tunnel syndrome, discogenic back discomfort or sciatic pain. Cranial nerve involvement has also been described. The cause of these symptoms may not be easily detected because lesions may be located proximally and cause distal complaints. Patient complaints are present in 33% of cases .
Different types of neurilemmoma have been described: plexiform , cellular, ancient, solitary, melanotic   and plexiform melanocytic . Less frequently encountered variants include malignant epithelioid schwannoma without neurofibromatosis , cutaneous pseudoglandular schwannoma , neuroblastomalike/rosetoid schwannoma  and plexiform multinodular neurilemomma . Lesions can also be found as part of genetic syndromes: schwannomatosis, type 1 or 2 neurofibromatosis and the Carney complex. The tumor may compress neighboring structures, causing various symptoms. Rare locations include the subungal  and lip  areas, whereas commonly involved nerves are vagus, cervical, ulnar and peroneal. Both sensory and motor nerves may be affected and functional deficit may be encountered.
Neurilemmomas are benign tumors with no malignancy potential, except for 10% of the melanotic type.
With noncontributory hematological and biochemical workup, neurilemmoma diagnosis relies on history and clinical evaluation, as well as imaging and histologic examination.
Plain radiographies often reveal non specific aspects, as these tumors are radiolucent, while ultrasonography is a reliable diagnosis method . More information is added by computerized tomography or magnetic resonance scanning, that describe a usually round mass, no bigger than 2,5 cm that uniformly enhances when gadolinium contrast is administered.
If doubt persists and a biopsy is needed or symptoms dictate excision, histology provides further description. The tumor is unilocular and surrounded by a vascularized capsule composed of epineurium. Neurilemmomas contain benign spindle cells (Antoni A areas) and connective tissue (Antoni B areas) with no mitotic figures, and may contain calcification or hemorrhage areas or degenerative cysts. The grade of the tumor depends on how aggressive the growth is. Immunohistochemistry is positive for vimentin, keratin, glial fibrillary acid protein, neuron-specific enolase and myelin basic protein   and negative for masson trichrome stain. Leu7, S-100 protein and epithelial membrane antigen are present . In degenerate tumors, the most valuable diagnostic tool is S-100 protein antibody stain, as it highlights beyond doubt the presence of Schwann cells in the tumor.