Axillary Nerve Schwannoma: A Rare Case Report.

Primary tumors of the brachial plexus are a rare cause of an axillary swelling. Schwannomas are benign tumors arising from Schwann cells. Most of the schwannomas occur in the head and neck region and in the flexor aspect of the limbs. We present a case of a 60-year-old female who presented with pain in the left axilla radiating to the left upper limb since 2 years and a painful swelling in her left axilla for 3 months. The diagnosis is made by fine needle aspiration cytology and magnetic resonance imaging, and confirmed by histopathological examination as schwannoma.

Introduction

Schwannomas are benign encapsulated perineural tumors arising from Schwann cells of nerve sheath of peripheral or cranial nerves. About 25% of all schwannomas occur in the head and neck region. They rarely occur in the axillary nerve or brachial plexus. We report here one such case of an axillary schwannoma, which is rare and unusual in its site of occurrence.

Case Report

A 60-year-old female patient presented to Victoria Hospital with pain in the left axilla since 2 years, insidious in onset, radiating to left upper limb and associated with tingling sensation up to the tip of all fingers. She noticed a painful swelling in her left axilla 3 months back. On examination, a solitary, tender, firm swelling of 4 cm × 3 cm in its greatest dimension was situated in the left axilla. Lymph nodes were not palpable. There were no neurological deficits detected on the left upper limb.

All hematological investigations were within normal limits. Fine-needle aspiration cytology showed several fragments of closely packed, oval to spindle cells with focal, minimal atypia and few fragments of fibrous tissue, suggestive of a benign cellular spindle lesion. Ultrasound of left axilla showed well-defined hypoechoic lesion measuring 2.5 cm × 2.5 cm with internal vascularity, giving the differential diagnosis of lymph node, or soft tissue tumor (nerve sheath tumor). Magnetic resonance imaging (MRI) showed a well-defined solid, homogeneously enhancing, T1 hypo and T2/proton density fat saturation hyperintense lesion continuous with the axillary nerve sheath in left axillary fat with no locoregional lymphadenopathy [Figure 1a–d].

Figure 1

(a) Axillary swelling, preoperative. (b-d) Magnetic resonance image showing well-defined solid, homogeneously enhancing, T1 hypo and T2/proton density fat saturation hyperintense lesion continuous with the axillary nerve sheath (white arrow = axillary nerve,

The patient underwent excision of the tumor that was found to be arising from the axillary nerve sheath [Figure 2a–d]. The patient did not have any neurological deficit after the procedure, except for the pain in the axilla. Post-operatively and after discharge, the patient was advised physiotherapy. The patient came for follow-up after 1 month without any neurological deficit. Histopathological examination (HPE) showed encapsulated lesion consisting of proliferating fibroblasts with scanty collagen and organoid arrangement of cells at places, without cellular atypia, suggestive of schwannoma.

Figure 2

(a) Intraoperative photo showing the tumor continuous with axillary nerve. (b) Intraoperative photo showing axillary nerve dissected from the tumor. (c) Intraoperative photo showing the axillary nerve after excision of the tumor. (d) Gross tumor specimen after removal

Discussion

Schwannoma (neurilemmoma) is a benign tumor, arising from Schwann cells.[1] They usually have a peak incidence in the third to fifth decades of life, affecting both sexes equally. Schwannoma is a slow growing, solitary, firm, well-circumscribed, and encapsulated round or ovoid tumor[2] ranging from 1.5 to 3 cm in diameter.[34] The presence of large tumors, as well as rare cases of multiple neoplasms, has been reported.[567] An extracranial schwannoma may present as a solitary swelling anywhere in the body, the most common sites being the head and neck, flexor surfaces of the upper and lower limbs, posterior mediastinum in the thorax and on the trunk.[8] However, a schwannoma in the axilla is of unusual occurrence, such that a schwannoma presenting as a brachial plexus tumor accounts to only about 5% of Schwannomas.[9] Thus, on account of their rare occurrence and involvement of unusual sites, they pose a significant challenge to diagnosis and treatment.

MRI is an important and preferred diagnostic tool. On imaging scans, schwannoma is visualized as a well-defined homogeneously enhancing lesion, usually fusiform in shape, isointense to surrounding muscles on T1-weighted images, and hyperintense on T2-weighted images and enhanced with gadolinium.[10] Biopsy for HPE is also an important tool for diagnosis. On HPE, schwannomas are found to contain a varying proportion of two different areas. Antoni type A areas are highly cellular and contain closely packed spindle-shaped cells forming palisades called Verocay bodies. Antoni type B areas are composed of loosely arranged spindle-shaped cells in a mucinous matrix.[11]

The first choice of treatment for schwannoma is surgical excision of the tumor, while sparing the nerve trunk to avoid neurological deficits. Extracapsular excision is a commonly used operative technique in this regard. The intracapsular technique was used by Date et al.[12] Reports comparing results obtained after extracapsular and intracapsular enucleation of schwannoma have found the latter to be a better technique due to lower risk of complications.[12]

However, determining the margins of tumor excision is always difficult and controversial. The involved nerve may have to be sometimes sacrificed to achieve complete resection of the tumor. A significant risk of neurological complications is associated with any intraoperative damage to nerve fascicles. In recent reports, intraoperative nerve action potential recording has been shown to avoid nerve damage during the procedure.[13]

Conclusion

We have presented a rare case of axillary schwannoma. They pose a significant challenge to diagnosis on account of their rare occurrence in unusual sites. Hence, a clinician has to bear in mind the possibility of a schwannoma in patients presenting with a swelling in the axilla. MRI has a valuable diagnostic importance, and surgical excision of these tumors is associated with a good prognosis.

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Conflicts of interest

There are no conflicts of interest.