Noting schwannomas rarely arise in the foot and ankle alone, these authors discuss the treatment of cellular schwannoma in the fifth toe in a 23-year-old patient.
The fifth digit is a frequent site for various podiatric medical pathologies yet it is uncommon to consider the likelihood of a peripheral nerve tumor in our differential diagnoses. Peripheral nerve sheath tumors rarely occur in the foot and ankle region, accounting for only 10 percent of all soft tissue tumors in the foot and ankle.1 Most authors agree peripheral nerve sheath tumors occur between the second and fifth decades of life.2 There is reportedly no predilection for race or ethnicity, and gender distribution is equal.2
Schwannomas are the most common solitary tumors of the peripheral nervous system.3 They are benign neoplasms that are slowly progressive, originating from the Schwann cells along a peripheral nerve sheath.4 Typically encapsulated, schwannomas can be characterized by a homogenous arrangement of Verocay bodies and spindle-shaped cells that are in hypercellular (Antoni A) and hypocellular (Antoni B) sections.5 Aside from the olfactory and optic nerves, cellular schwannomas mostly occur in the neck, posterior mediastinum or pelvic region.6 Ankle and pedal schwannomas alone are rare, but the present case is a cellular schwannoma of a fifth digit.7
A Closer Look At The Patient Presentation
A 23-year-old woman presented to the office complaining of a painful “lump” on the outside of the fifth digit of her left foot. She first noticed the mass approximately four years prior to this visit and relates the mass had significantly increased in size since that time. The patient denied any form of trauma or foreign body to the area.
As the mass became larger, she noted the pain level and sensations worsened. Her pain was mainly a “dull ache with occasional burning and tingling.” She was unable to wear certain shoe gear as the lateral compression on the forefoot exacerbated these symptoms. The patient works as a coffee shop attendant, laboring on her feet most of the day. Her medical history is unremarkable. She only takes prenatal vitamins and has no known allergies.
Physical examination of the left fifth digit revealed a well-circumscribed, non-pulsatile, nodular mass that was immobile. The mass was localized along the plantar lateral aspect of the fifth digit, extending from the level of the proximal interphalangeal joint to the distal tuft. Palpation of the mass yielded a “sharp, burning” sensation while active range of motion (ROM) at the level of the proximal interphalangeal joint elicited the “achy” pain. Vascular examination showed normal pedal pulses and capillary refill time was equal to all digits. Lower extremity reflexes were within normal limits and protective sensation was intact to all points bilaterally. The patient demonstrated a rectus foot type upon weightbearing.
Plain radiographs showed soft tissue swelling but no osseous involvement or pathology. Magnetic resonance imaging (MRI) revealed a soft tissue lesion plantar to the distal and middle phalanges of the fifth digit, measuring approximately 2.1 cm long x 1.2 cm wide x 0.1 cm deep. The lesion appeared to be well encapsulated and showed high signal intensity on T2 weighted imaging (see Figure 1). The osseous structures of the forefoot were normal.
We scheduled an outpatient procedure to excise the soft tissue mass from the left fifth digit. We made a dorsolateral incision from the level of the base of the fifth proximal phalanx, extending distally, approximately 2 cm in length (see Figure 2). We completely excised the mass with a combination of careful sharp and blunt dissection. The mass we removed from the operative field was an unequal lobulated mass (see Figure 3). The proximal portion of the lesion was more than twice the size of the smaller distal section. There were no osseous or periosteal tissues involved, and no tendinous attachments were visible intraoperatively. We subsequently sent the mass for pathologic examination.
The gross pathologic examination was of “a transected pink-tan soft tissue mass, which (measured) 3.0 x 1.5 x 1.3 cm. The outer aspect appears to have a fibrous capsule. The specimen was sectioned, revealing a yellowish-tan soft tissue lesion, which is firm and solid, (but) appears to be lymphomatous.” The pathology report revealed a cellular schwannoma. Specifically, the composition of the tumor was “spindle-shaped cells showing vague Antoni A and B patterns.” The calculated mitotic rate was in the acceptable range of a cellular schwannoma. Immunohistochemical staining showed “strong positivity with S100 and CD34,” which is likely indicative of a neural tumor rather than smooth muscle tumor.
What You Should Know About Cellular Schwannomas
The most important aspect of dealing with any soft tissue tumor is determining whether it is benign or malignant as this may be the most influential prognostic factor. One must rule out malignancy through proper tissue sampling and histological analysis.3 Benign solitary cellular schwannomas rarely become malignant but accurate diagnosis is key to providing adequate and efficient treatment.8 Biopsy and immunohistochemical staining are essential components of the surgical process when obtaining a definitive diagnosis.9 Surgical resection of these tumors is the mainstay of treatment. However, these tumors do not require radical excision but simple resection ensuring preservation of the involved peripheral nerve.10
This is a unique case of a benign cellular schwannoma located within a fifth digit. Only one other such case was evident in the literature. Wolp and Johnson reported a fifth digit schwannoma involving a simple excision without complication.8 Complications have been associated with these solitary lesions. Nath and colleagues reported a case of a non-healing ulcer on a hallux secondary to cellular schwannoma. After six months of local wound care treatments, a biopsy of the ulcer indicated a benign schwannoma.11
Our patient’s postoperative course was unremarkable and without complication. She has since returned to normal daily activities, including full-time at work, with no recurrence of pain or symptoms. The incision has healed well with no hypertrophic cicatrix or hyperpigmentation about the operative site.
Dr. Ciano is a Podiatric Attending Surgeon at the VA Medical Center in Providence, R.I.
Dr. Reuter is affiliated with the Department of Podiatric Surgery at Roger Williams Medical Center in Providence, R.I. He is board-certified in foot and ankle surgery by the American Board of Podiatric Surgery, and a Fellow of the American College of Foot and Anklev Surgeons.
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