A 49-year-old woman presented with an asymptomatic lesion on the right side of her neck that had been present for approximately 10 years. Over time, the lesion had slowly increased in size. There was no history of antecedent trauma to the area or discharge from the lesion. Her past health was unremarkable. There was no personal or family history suggestive of neurofibromatosis, schwannomatosis, or similar such lesions.
Physical examination revealed a nontender, smooth-surfaced, skin-colored, firm, multinodular mass on the right side of her neck. The mass was subcutaneous and measured 2.0 × 2.5 cm. The mass was mobile from side to side but not in a vertical direction. The Tinel sign (paresthesia upon percussion of the lesion) was negative. No similar lesions were observed elsewhere on the body. The remainder of the clinical examination revealed no abnormalities. In particular, there were no café au lait patches, axillary freckling, or Lisch nodules.
Answer: Plexiform schwannomaSee the full case at Consultant360
An excisional biopsy of the mass was performed. Examination of the gross specimen showed an encapsulated multinodular tumor with a fairly firm and smooth surface.
Histologically, the tumor consisted of varying hypertrophic nerve fascicules showing a plexiform pattern, along with fibrous connective tissue. The tumor was mainly composed of hypercellular Antoni A areas consisting of tightly spaced spindle-shaped cells with palisading nuclei. Hypocellular Antoni B areas consisting of gelatinous and microcytic tissue with a loose meshwork of cells were also seen. There were no signs of pleomorphism, mitosis, hemorrhage, or necrosis. Immunohistochemical analysis revealed that the tumor cells were strongly positive for S-100 protein.
Based on the clinical and histologic findings, a diagnosis of plexiform schwannoma was established. After surgical excision, the postoperative course was uneventful. Three years postoperatively, there had been no clinical recurrence of the lesion.
Plexiform or multinodular schwannoma is a benign tumor originating from the Schwann cell of the nerve sheath, characterized by plexiform or multinodular growth patterns both grossly and microscopically.1-3 The condition was first described in 1970 by Masson, which he called “plexiform schwannogliosis.”4 The term plexiform schwannoma was coined in 1978 by Harkin and colleagues, who reported on 6 patients aged 9 to 39 years with the condition and recognized this disease entity as a distinct variant of schwannoma.5 Plexiform schwannomas differ from conventional schwannomas that grow as a globular mass within a single fascicle of an often multifascicular nerve.6 Rather, plexiform schwannomas typically appear as multinodular and often affect multiple fascicles.6
Schwannomas account for 28% to 36% of peripheral nerve sheath tumors.7,8 Plexiform schwannomas account for 2% to 5% of all schwannomas.9-12
The vast majority of plexiform schwannomas cases occur in adults between 20 and 50 years of age.2,7 The condition may, however, arise at any age, including during childhood.2 There is no sex or racial predilection.11-13 The occurrence is usually sporadic, although it can be associated with neurofibromatosis type 2 and schwannomatosis.9,14
The exact etiopathogenesis is not known. Trauma might play an etiologic role in at least some cases.11,12,14 The vast majority of plexiform schwannomas involve small nerves in the dermal or subcutaneous tissue.
Characteristically, plexiform schwannomas are composed of multiple intradermal or subcutaneous encapsulated tan nodules separated by fibrous septa.2,14 Histologically, the nodules are composed predominantly of cellular Antoni A areas consisting of slender spindle cells with frequent nuclear palisades and Verocay bodies.1,2,11,14 Antoni B areas, which are hypocellular degenerative areas composed of spindle cells distributed in a haphazard manner in a loose stroma, may also be seen.15 Immunostaining for S-100 protein is strongly and diffusely positive.15 S-100 protein is an acidic protein in the nucleus and cytoplasm of Schwann cells.15
Typically, a plexiform schwannoma presents as an asymptomatic, solitary, slow-growing, well-circumscribed, soft to rubbery, nontender nodule.16 The average diameter is approximately 2 cm.2 The mass is generally mobile from side to side but not in a vertical direction.2 Pain is unusual because the tumor displaces but does not invade the nerve.14 Occasionally, paresthesia in the distribution of the involved nerve may be elicited with pressure/percussion over the lesion (Tinel sign).
The tumor usually occurs in the dermal and subcutaneous tissue.7,11 Rarely, skeletal muscle and deep somatic soft tissue may be affected.1,17 Sites of predilection include the head and neck followed by the trunk and upper extremities.7,9,15,17 Plexiform schwannomas are traditionally solitary.9,13,14 Multiple plexiform schwannomas occurring in the same patient have rarely been reported.16
Diagnosis and Laboratory Investigations
The diagnosis is usually suspected clinically based on typical physical features and is confirmed histologically based on the characteristic histologic findings. Magnetic resonance imaging is useful to distinguish a plexiform schwannoma from a conventional schwannoma and to define the extent of a deep-seated lesion.3,6
The main differential diagnosis is a plexiform neurofibroma. A plexiform neurofibroma can be present at birth or develop early in childhood.12 It has the appearance of a serpentine “bag of worms.”11,12 Histologically, a plexiform neurofibroma is characterized by a disorganized array of Schwann cells, fibroblasts, and axons with wiry cytoplasmic processes.15 A plexiform neurofibroma is pathognomonic of neurofibromatosis type 1 and carries a significant risk of malignant transformation.12,15,17
Other differential diagnoses include schwannomatosis, malignant peripheral nerve sheath tumor, traumatic neuroma, perineurinoma, epidermoid cyst, dermoid cyst, hemangioma, lipoma, angiolipoma, lymphangioma, leiomyoma, and eccrine spiradenoma.3
Complications and Prognosis
A plexiform schwannoma is cosmetically unsightly and may have an adverse impact on quality of life. The condition may be associated with neurofibromatosis type 2, especially when multiple lesions are present or when the onset is in childhood.9,14,17,18 There is no association with neurofibromatosis type 1.3,7,15 Also, there is no propensity for malignant transformation.1,2,15,19
Without treatment, plexiform schwannomas usually grow slowly and persist indefinitely.
The treatment of choice is complete surgical excision with free margins, with the best possible attempt to preserve the functional nerve trunk.14
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17. Ko JY, Kim JE, Kim YH, Ro YS. Cutaneous plexiform schwannoma in a patient with neurofibromatosis type 2. Ann Dermatol. 2009;21(4):402-405.
18. Miyakawa T, Kamada N, Kobayashi T, et al. Neurofibromatosis type 2 in an infant with multiple plexiform schwannomas as first symptom. J Dermatol. 2007;34(1):60-64.
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