Pseudoglandular schwannoma of the cauda equina. Case report

Multiple schwannomas with pseudoglandular element synchronously occurring under the tongue: A case report

BACKGROUND

Schwannoma is a rare benign, encapsulated tumor of the nerve sheath under the tongue, mostly occurring as solitary tumors with classical histological pattern and several common morphological variants. To our knowledge, multiple schwannomas with pseudoglandular element synchronously occurring under the tongue are rare; we report herein the first such case.

CASE SUMMARY

A 53-year-old man had first noticed an isolated asymptomatic mass under the tongue, and as the mass grew, the tongue was elevated. Physical examination showed multiple oval neoplasms, and the overlying mucosa was normal. Computed tomography showed three low-density oval neoplasms under the tongue, which were cystic-solid with unclear boundary. The patient has no cutaneous tumors, VIII nerve tumors, or lens opacities and no history of neurofibromatosis 2 or confirmed schwannomatosis in any first-degree relative. Magnetic resonance imaging showed no evidence of vestibular schwannoma. The preoperative diagnosis was mucoepidermoid carcinoma. During hospitalization, all neoplasms were completely excised by surgeons through an intraoral approach under general anesthesia. The diagnosis of the multiple schwannomas with pseudoglandular element was made by histopathology after surgery. At the 15-mo follow-up visit, the patient had no sign of recurrence or development of other peripheral nerve tumors.

CONCLUSION

Although rare, multiple schwannomas with pseudoglandular element do exist in patients presenting with masses under the tongue. Oral surgeons should be aware of the existence of multiple schwannomas with pseudoglandular element when considering masses under the tongue due to the different prognosis between multiple schwannomas with pseudoglandular element and mucoepidermoid carcinoma.

Schwannomas with pseudoglandular elements: clinicopathologic study of 61 cases

Schwannomas are benign neoplasms of peripheral nerve sheath. A number of morphologic variants of schwannoma have been described. The pseudoglandular variant is very rare. We retrieved and reviewed hematoxylin and eosin slides of all cases of schwannoma reported between 2007 and 2014 to look for pseudoglandular elements. Pseudoglandular cystic spaces were seen in 61 (6.3%) of 971 schwannomas diagnosed during the study period. Of these 61 cases, 56 (91.8%) were located in the spinal nerve roots. The majority (60.6%) were male. Mean age in these 61 cases was 41 years. Mean tumor size was 3.5 cm. All 61 cases showed typical Antoni A and Antoni B areas with multiple pseudoglandular cystic spaces scattered throughout. These areas were lined by flat to cuboidal cells which showed positivity for immunohistochemical stain S-100 and were negative for epithelial membrane antigen. An average of 7 pseudoglandular cystic spaces was noted per case. In conclusion, pseudoglandular cystic spaces are lined by Schwann cells and most likely represent degenerative changes in schwannoma probably degenerated Verocay bodies. They are rare albeit well-defined features seen in a significant though small number of schwannomas. It is important not to mistake them for other neoplasms. Larger studies are required to determine predilection of these changes in spinal nerve root schwannomas as seen in our series.

Schwannomas and their pathogenesis

Schwannomas may occur spontaneously, or in the context of a familial tumor syndrome such as neurofibromatosis type 2 (NF2), schwannomatosis and Carney's complex. Schwannomas have a variety of morphological appearances, but they behave as World Health Organization (WHO) grade I tumors, and only very rarely undergo malignant transformation. Central to the pathogenesis of these tumors is loss of function of merlin, either by direct genetic change involving the NF2 gene on chromosome 22 or secondarily to merlin inactivation. The genetic pathways and morphological features of schwannomas associated with different genetic syndromes will be discussed. Merlin has multiple functions, including within the nucleus and at the cell membrane, and this review summarizes our current understanding of the mechanisms by which merlin loss is involved in schwannoma pathogenesis, highlighting potential areas for therapeutic intervention.