Microcystic/Reticular Schwannoma Occurring in the Lumbar Spine: A Rare Case Report

Abstract

Microcystic/reticular schwannoma (MRS) is a rare subtype of schwannoma characterized by distinctive histological features. It mainly occurs in the head-and-neck region and extremities. We present a case of MRS occurring in the lumbar spine, which is an exceedingly rare location for this tumor. This is the case of a middle-aged woman who presented with complaints of lower back pain radiating to the left lower limb. Magnetic resonance imaging demonstrated features suggestive of a myxopapillary ependymoma arising from the cauda equina at the L4–L5 vertebral level. Diagnosis of MRS was made based on the typical histopathological features and immunohistochemical positivity for the S100 marker. MRS is a rare subtype of schwannoma, which differs from classical schwannoma in several aspects. Raising awareness regarding this subtype is essential to budding pathologists to prevent their misdiagnosis as myxopapillary ependymoma.

INTRODUCTION

Schwannomas are benign nerve sheath tumors originating from Schwann cells, commonly found in peripheral nerves of the head, neck, and extremities.[1] Microcystic/reticular schwannoma (MRS) is a new and rarer variant of schwannoma, it was initially described by Liegl et al. in 2008 with a predilection for the visceral organs.[2] It is characterized by a distinctive microcystic and reticular growth pattern histologically.[3] MRS typically presents as a slow-growing, painless mass and has been reported in various anatomical locations, predominantly in the soft tissues of the extremities.[4] MRS of the spine is extremely rare, with only one case of cervical spine and two cases of lumber spine reported till date.[5,6,7] Here, we report a case of MRS located in the lumbar spine. To the best of our knowledge, this will be the third case of MRS in the lumber spine reported worldwide.

CASE REPORT

Case presentation

A 32-year-old woman presented with a 6-month history of progressively worsening lower back pain radiating to the left lower limb. He reported occasional episodes of numbness and tingling in the left leg but denied any motor weakness or bladder/bowel dysfunction. Physical examination revealed tenderness over the lumbar region with no neurological deficits.

Investigation

Magnetic resonance imaging (MRI) of the lumbar-sacral spine demonstrated a T1 intermediate to hypointense and T2 intermediate to hyperintense signal mass seen in the cauda equina region of the lumbar spinal canal at the L2–L3 level on MRI measuring approximately 39 mm × 13 mm in size. Based on the clinical and radiological findings, a provisional diagnosis of myxopapillary ependymoma was made.

Surgical management

The patient underwent an L2–L3 laminectomy for excision of the tumor. Intraoperatively, a whitish-to-yellowish, unencapsulated mass adherent to the left L3 nerve root was encountered. Gross total resection of the tumor was achieved, preserving the nerve root integrity. After that specimen was sent for histopathological examination.

Histopathological examination

Gross

The specimen measured 4.0 cm × 1.3 cm × 1.2 cm in dimension. The outer surface was smooth and shiny. Cut surface was soft. The cut surface showed a well-circumscribed tumor, grayish-to-brownish in color with multiple small cystic spaces, and had a soft, gelatinous texture [Figure 1].

Figure 1.

(a) MRI showing an intradural extramedullary mass at the L2–L3 level (arrow indicates the lesion). (b) Grossly, well-circumscribed tumor with attached nerve root. (c) The Cut surface showed numerous microcytic areas. (d and e) H- and E-stained sections showed numerous microcystic and reticular patterns of tumor cells. (f) Immunohistochemistry showed S-100 positivity in tumor cells

Microscopic examination

Sections revealed a benign tumor composed of spindle cells arranged in intersecting fascicles with a reticular growth pattern. The tumor cells exhibited elongated nuclei with inconspicuous nucleoli and scant cytoplasm. Numerous microcysts filled with eosinophilic material were dispersed throughout the tumor. Verocay bodies and thick-walled blood vessels were not seen. There is no evidence of nuclear atypia, necrosis, and atypical mitosis [Figure 1]. Immunohistochemical staining showed positive staining for S-100 protein, confirming the Schwann cell origin of the tumor. The histological features and immunohistochemistry (IHC) were consistent with a diagnosis of MRS.

Postoperative course

The patient had an uneventful postoperative course with a resolution of his preoperative symptoms. Follow-up MRI of the lumbar spine performed 3 months after surgery showed no evidence of residual or recurrent tumor.

DISCUSSION

Schwannoma is a benign peripheral nerve sheath tumor. It usually occurs in the fourth decade of life and there is no sex predilection.[8] It typically presents as a slow-growing mass, often associated with nerve roots or peripheral nerves.[1] While schwannomas are commonly found in the head, neck, and soft-tissue extremities, occurrence in the spine is exceedingly rare, with limited reported cases.[5] The lumber spine location is a very rare location for schwannoma. According to the literature, only two cases of lumber spine location were reported.[6,7] Our case is the third case of lumber spine location of schwannoma.

Based on the clinicoradiological examination, differential diagnoses of spinal MRS include neurofibromas with extensive myxoid degeneration, microcystic and myxoid meningiomas, and myxopapillary ependymoma.[7,9] In our case, the radiological provisional diagnosis was myxopapillary ependymoma. This finding is consistent with the finding of Ando et al.[9] Definitive diagnosis relies on histopathological examination, which reveals the characteristic microcystic and reticular growth pattern of the MRS.[10]

Several morphologic variants of schwannoma are well recognized and include classical, plexiform, ancient, cellular, melanotic, epithelioid, glandular, and hybrid forms of schwannoma with neurofibroma and perineurioma.[8,10] MRS is an uncommon subtype of schwannoma, with only a few cases approximately 37 have been reported in the literature.[3] MRS differs from classical schwannoma based on histomorphology.[6] Histopathological examination of classical schwannoma typically exhibits a biphasic pattern of spindle cells with Antoni A and Antoni B area and thickened hyalinized walled blood vessels. These characteristic features are hallmarks of classical schwannoma.[11] Complete surgical excision is the treatment of choice for microcystic/reticular schwannoma, with an emphasis on total tumor removal while preserving neurological function.[6,7] MRS has spindle-shaped tumor cells arranged in unique microcystic and reticular patterns. In our case, these two unique patterns are present while Antoni A and Antoni B areas with thickened hyalinized walled blood vessels are absent.[2,3,4] Our findings were consistent with the findings of Li et al., Liu et al., and Tripathi et al. who also reported similar histomorphology in their respective cases of lumber spinal schwannomas.[5,6,7]

IHC plays an important role in the differential diagnosis of MRS. In our case, tumor cells showed diffuse and strong nuclear as well as cytoplasmic positivity for S-100. This finding corresponds to various literature.[3,4,10] Fritchie et al. first time identified specific genetic characteristics in the MRSs which showed TFE3 fusion with the NONO gene and overexpression of the ALK gene. These specific genetic alterations may have implications for diagnosis, prognosis, and potential targeted therapies for the affected individuals.[12] Surgical excision remains the primary treatment modality for MRS, aiming for complete resection while preserving neurological function. The prognosis following surgical resection is excellent, with low rates of recurrence reported in the literature.[1,4,6,7]

CONCLUSION

MRS is a rare subtype of schwannoma, and its occurrence in the lumbar spine is exceptionally uncommon. Clinicians should consider MRS in the differential diagnosis of intradural extramedullary spinal masses. Raising awareness regarding this subtype is essential to budding pathologists to prevent their misdiagnosis. Further studies are warranted to elucidate the optimal management of this rare tumor entity.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that her name and initials will not be published and due efforts will be made to conceal her identity, but anonymity cannot be guaranteed.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.