Dermal nerve sheath myxoma

Dermal nerve sheath myxomas are benign peripheral nerve sheath tumors usually originating from the skin or subcutaneous tissues.

Terminology

The previous term was ‘classic or myxoid variant of neurothekeoma’ but recent 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 tumors (5^th 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 tumors. 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.

Etiology

The etiology 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
• tumor 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

Tumors 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
• schwannoma