Dermal nerve sheath myxomas are benign peripheral nerve sheath tumours usually originating from the skin or subcutaneous tissues.
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Terminology
The previous term was ‘classic or myxoid variant of neurothekeoma’ but data has shown that they are biologically and clinically distinct from neurothekeoma 1,2.
Diagnosis
The diagnosis of dermal nerve sheath myxoma is established by a combination of clinical, histological and immunohistochemical features 1.
Diagnostic criteria
Diagnostic criteria according to the WHO classification of soft tissue and bone tumours (5th edition) 1:
small superficial lesions of the distal extremities in young adult patients
multilobulated myxoid neoplasm
consisting of bland spindle cells and epithelioid Schwann cells
immunoreactivity for S100
Epidemiology
Dermal nerve sheath myxomas are rare tumours. They occur in a wide age range with a peak in the fourth decade of life. Men are slightly more frequently affected 1,4.
Clinical presentation
They are usually slow-growing and otherwise asymptomatic. Sometimes they can be painful 1.
Pathology
Dermal nerve sheath myxomas are myxoid neoplasms with a multinodular growth pattern consisting of bland spindle cells and epithelioid Schwann cells 1.
Aetiology
The aetiology is unknown 1.
Location
Dermal nerve sheath myxomas are often found in the dermis and subcutis of extremities, in particular, the fingers knees and toes. They also can be rarely found around the spinal canal 1-3.
Macroscopic appearance
Macroscopically dermal nerve sheath myxomas are well-delineated shimmering white to translucent nodules of a firm to rubbery consistency. They have varying sizes on detection but most are small and less than 2.5 cm 1.
Microscopic appearance
Histological features of dermal nerve sheath myxomas include the following 1-4:
multinodular growth pattern
abundant myxoid matrix surrounded by a prominent crust of fibrous tissue
small epithelioid ring-like stellate or spindled neoplastic Schwann cells arranged in cords or nests
mild nuclear atypia
few mitoses
Immunophenotype
Neoplastic Schwann cells should be diffusely positive S100 and show reactivity to GFAP, and CD57 on immunohistochemistry stains. The surrounding fibrous connective tissue should respond to collagen IV 1-4.
Radiographic features
Ultrasound
On ultrasound, dermal nerve sheath myxomas have been described as lobulated and with a heterogeneous hyperechoic echotexture 4.
MRI
On MRI dermal nerve sheath myxomas have been described as a well-defined lesion with the following signal characteristics 4,5:
T1: isointense compared to muscle
T2: hyperintense
T1 C+ (Gd): enhancement
Radiology report
The radiological report should include a description of the following:
form, location and size
tumour margins and transition zone
relations to the muscular fascia
relations to bones
relations to neurovascular structures
Treatment and prognosis
Management of dermal nerve sheath myxomas usually consists of complete excision. However, they feature a high recurrence rate of up to 47% which can occur repeatedly 1.
History and etymology
Dermal nerve sheath myxomas were first reported in the literature by two American pathologists, James C. Harkin and Richard Jay Reed in 1969 2,3,6.
Differential diagnosis
Tumours or conditions which can mimic the presentation and/or appearance of dermal nerve sheath myxomas include:
cellular neurothekeoma: more common in the head and neck area
acral fibromyxoma: often near the nailbed
plexiform neurofibroma: often associated with neurofibromatosis type 1
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