Ancient schwannoma of the gluteal region: a case report

Abstract

Schwannomas are benign peripheral nerve sheath tumors that rarely develop in the gluteal region. We describe a 35-year-old man with a 5-year history of a slowly enlarging left gluteal mass, which became painful after superficial ulceration developed. Ultrasonography and magnetic resonance imaging demonstrated a well-circumscribed, heterogeneously enhancing solid lesion without evidence of invasion. Because malignancy could not be excluded on imaging, the mass was excised en bloc with clean margins without prior biopsy. Histopathology revealed encapsulated spindle cells arranged in a palisading pattern, with cystic degeneration and hemorrhage; immunohistochemistry was positive for S100, vimentin and calponin, confirming the diagnosis of ancient schwannoma. No recurrence occurred during 3 years of follow-up. Schwannoma should be considered in the differential diagnosis of gluteal mass, even in the absence of a positive Tinel sign.

Introduction

Schwannoma is the most common benign nerve sheath tumor of peripheral nerves and arises from Schwann cells [1]. It accounts for 1%–3% of peripheral nerve tumors and most commonly involves the head, neck, and upper extremities. Schwannomas are usually solitary, slow-growing masses and are rarely symptomatic, which often delays diagnosis [1–3]. Peripheral nerve sheath tumors of the lower extremity represent 9% of all such tumors and are most frequently located in the spinal nerves and the brachial plexus. To our knowledge, the sciatic and tibial nerves are the most common sites of schwannoma in the lower extremity [4, 5], whereas schwannoma of the gluteal region is exceedingly rare. Here, we report a case of schwannoma of the gluteal region in a 35-year-old man.

Case report

A 35-year-old man presented with pain, swelling, and an ulcerated skin lesion over the medial aspect of the left gluteal region. The mass had reportedly been present for 5 years and had gradually enlarged over time. Over the preceding 3 months, superficial ulceration developed, and the patient—whose occupation required prolonged sitting—began experiencing pain, prompting him to seek medical attention. There was no preoperative neurovascular deficit.

Ultrasonography revealed a well-circumscribed, heterogeneous, hypoechoic subcutaneous solid lesion measuring 43 × 20 mm in the left gluteal region, without significant vascularity. Magnetic resonance imaging (MRI) demonstrated a 72 × 38 mm, well-defined, solid, heterogeneous, markedly contrast-enhancing lesion containing areas of fat and fluid intensity in the medial left gluteal region, without evident invasion (Fig. 1). No nerve from which the lesion originated could be identified.

Figure 1.

(a) Transverse T1-weighted image showing hypointense mass. (b) Transverse T2-weighted image showing peripheral hipointensity and central hyperintensity. (c) Sagittal T1-weighted contrast-enhanced image showing well-defined peripheral contrast. (d) Transverse T1-weighted contrast-enhanced image showing heterogeneous hyperintense contrast.

Because of the heterogeneous internal structure raising concern for malignancy, and because the extent of soft tissue allowed for wide surgical margins, the tumor was resected en bloc with clean surgical margins without prior biopsy (Fig. 2).

Figure 2.

(a) Posterior view showing superficial ulceration on the skin. (b and c) Medial lateral view showing superficial ulceration and resected normal fatty tissue. (d) Anterior view showing resected normal fatty tissue.

Histopathological examination revealed an encapsulated tumor within the dermis and subcutaneous fat, composed of spindle cells arranged in a fibrillary background with a palisading pattern. Hypocellular and hypercellular areas were observed together, along with cystic degeneration and hemorrhagic areas within the tumor. Focal areas of hyalinization and thick-walled vascular structures were observed. Hemosiderin-laden macrophages and a sparse infiltrate of mononuclear inflammatory cells were noted within the hyalinized stroma. Degenerative-type nuclear atypia, characterized by irregular, hyperchromatic, and multilobulated nuclei, was evident in the Schwann cells. Neither mitoses nor necrosis were observed.

Immunohistochemically, tumor cells stained positive for vimentin, S100, and calponin (Fig. 3). These findings were consistent with ancient schwannoma.

Figure 3.

(a) The lesion, composed of spindle cells surrounded by a fibrous capsule (H&E, ×40). (b) Oedema, cystic degeneration, and hemorrhagic areas within the lesion. Image showing focal areas of hyalinization, thick-walled vascular structures, hemosiderin-laden macrophages, and a sparse infiltrate of mononuclear inflammatory cells within the hyalinized stroma (H&E, ×40). (c) Image showing Verocay bodies formed by nuclear palisading. Degenerative-type nuclear atypia, characterized by irregular, hyperchromatic, and multilobulated nuclei, is observed in Schwann cells. (H&E, ×200). (d) Spindle cells of the lesion showing positive staining for S100 (immunoperoxidase, ×100).

Discussion

Schwannoma is the most common solitary nerve tumor. It is usually solitary and most often occurs in the head, neck, and upper extremities. Its etiology remains poorly understood, although some authors have suggested a role for traumatic factors and autosomal dominant inheritance in its development [5]. This tumor can occur at any age, with the highest incidence between 30 and 60 years and no sex predilection [6]. In our case, the patient was a 35-year-old obese man. Nevertheless, there was a size discrepancy between ultrasonography and MRI. We believe this difference stemmed from the failure to measure the peripheral zone of contrast enhancement—visible on MRI—during the ultrasound examination.

Schwannoma is a slow-growing, encapsulated tumor. The capsule originates from the perineurium of the parent nerve fascicle and is surrounded by a condensation of the deepest layers of the epineurium, with well-differentiated Schwann cells found within it [1, 7–9]. Schwannoma may remain asymptomatic until it causes a secondary pathology in the surrounding tissue. In our case, the patient’s mass had been asymptomatic for 5 years and became symptomatic only in the preceding 3 months, following superficial ulceration.

Radiological examination is used to exclude bone involvement or soft tissue abnormalities. On ultrasonography, schwannoma typically appears as a solid, well-circumscribed, oval, homogeneously hypoechoic mass. On MRI, schwannoma is isointense, or shows decreased signal relative to skeletal muscle on T1-weighted images and heterogeneously increased signal intensity on T2-weighted images [10–13]. Schwannomas typically enhance with contrast, showing central hyperintensity on T1-weighted images, while the periphery shows a well-defined hypointense ‘target sign’ indicating the presence of a capsule; on T2-weighted images, the center of the mass shows low signal intensity while the periphery shows high signal intensity [14]. In our case, a well-circumscribed, heterogeneously enhancing lesion was identified, with heterogeneous contrast enhancement on T1 and T2-weighted images.

Histologically, schwannoma is composed of hypocellular and hypercellular areas (Antoni A and B). Degenerative changes such as cyst formation, calcification, hemorrhage, and hyalinization may be present, and intratumoral axons are absent. Schwannomas are immunohistochemically positive for S100 protein [1, 8, 9, 11, 13, 15].

Microscopic enucleation is generally the preferred surgical approach. However, given the atypical location of the tumor and its heterogeneous contrast enhancement, which raised the possibility of malignant transformation, we performed a wide resection with clean surgical margins. No recurrence or additional complaints were observed during 3 years of follow-up with ultrasonography and MRI.

In conclusion, schwannoma is generally rare in the lower extremities and exceedingly rare in the gluteal region. Schwannoma should be considered in the differential diagnosis of a painless gluteal subcutaneous mass, even in the absence of a positive Tinel sign or a palpable nerve fascicle.

Author contributions

Ridvan Acar (Conceptualization, methodology, investigation, writing—original draft, funding acquisition) and Seyma Ozturk (Writing—original draft, writing—review and editing)

Conflicts of interest

The authors declare that they have no conflicts of interest.

Funding

This research received no external funding. All costs were covered by the first author.

Consent

Written informed consent was obtained from the patient for the publication of this case report and the accompanying images. The consent form is available from the corresponding author upon request.