Schwannomas are benign tumors exclusively composed of Schwann cells that arise from the peripheral nerve sheath; these tumors theoretically can present anywhere in the body where nerves reside. They tend to occur in the head and neck region (classically an acoustic neuroma) but also occur in other locations, including the retroperitoneal space and the extremities, particularly flexural surfaces. Patients with cutaneous schwannomas are most likely to present to their primary care provider’s office reporting skin findings or localized pain, and providers should be aware of schwannomas on the differential for painful nodular growths.
A 70-year-old man with type 2 diabetes mellitus presented to the primary care clinic for intermittent, sharp, localized left lower quadrant abdominal wall pain that was gradually progressive over the previous few months. The patient noticed the development of a small nodule 7 to 8 months prior to the visit, at which time the pain was less frequent and less severe. He reported no postprandial association of the pain, nausea, vomiting, diarrhea, constipation, or other gastrointestinal symptoms.
Ten months prior to the presentation, he was involved in a low-impact motor vehicle collision as a pedestrian in which he fell face-first onto the hood of an oncoming car. At that time, he did not note any abdominal trauma or pain. Evaluation at a local emergency department did not reveal any major injuries. In the interim, he had self-administered insulin in his abdominal region, as he had without incident for the previous 2 years. He reported that he was not injecting near the site of the nodule since it had formed. He could not recall whether the location was a previous insulin administration site.
On examination, the patient’s vital signs were normal as were the cardiac and respiratory examinations. An abdominal exam revealed normal bowel sounds and no overlying skin changes or discoloration. Palpation revealed a 1.5 x 1 cm rubbery-to-firm, well-circumscribed subcutaneous nodule along his mid-left abdomen, about 7 cm lateral to the umbilicus. The nodule was sensitive to both light touch and deep pressure. It was firmer than expected for an abdominal wall lipoma. There was no central puncta or pore to suggest an epidermal inclusion cyst. There was no surrounding erythema or induration to suggest an abscess.
The patient was referred for surgery and underwent excisional biopsy of the mass. Pathology revealed a well-circumscribed vascular/spindle-cell lesion consistent with a schwannoma. His postoperative course was uncomplicated. At 4-week follow-up the incision had healed completely and the patient was pain free.
Soft-tissue nodules are common—about two-thirds of soft-tissue tumors are classified into 7 diagnostic categories: lipoma and lipoma variants (16%), fibrous histiocytoma (13%), nodular fasciitis (11%), hemangioma (8%), fibromatosis (7%), neurofibroma (5%), and schwannoma (5%).1 Peripheral nerve tumors (schwannomas, neurofibromas) can be associated with pain or paresthesias, and less commonly, neurologic deficits, such as motor weakness. Peripheral nerve tumors have several classifications, such as nonneoplastic vs neoplastic, benign vs malignant, and sheath vs nonsheath origins. Schwannomas are considered part of the neoplastic subset due to their growth; otherwise, they are benign with a sheath origin. In contrast to neurofibromas, benign schwannomas have a slower rate of progression, lower association with pain, and fewer neurologic symptoms.2