Acral fibromyxoma

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Acral fibromyxomas are benign mesenchymal proliferations prone to recurrence usually found in the subungual and periungual sites of the digits.

Terminology

Superficial acral fibromyxoma or digital fibromyxoma are other acceptable names, the term cellular digital fibroma is no longer recommended .

Epidemiology

Acral fibromyxomas are rare. Most tumors are seen in middle-aged adults, however, they can occur in a wide age range. There is a male predilection.

Clinical presentation

They are slowly enlarging tumors and might be associated with nail deformity They can be painless or painful .

Associations

Associations with trauma have been described in rare cases .

Pathology

Acral fibromyxoma is a skin-based nonencapsulated fibroblastic proliferation leading to an infiltration of the subcutaneous tissue. They are characterized by lobular architecture with fascicular, palisading or storiform growth pattern .

Etiology

The etiology of acral fibromyxoma is unknown .

Location

Acral fibromyxomas are usually found in an acral periungual and subungual location of the fingers and toes. In rare occasions, they might be seen in other areas of the extremities as hands and feet ankles, wrists or lower legs and thighs.

Macroscopic appearance

Macroscopically acral fibromyxomas have a verrucoid or polypoid or lobulated appearance. They have poorly defined borders and a soft to firm consistency .

Microscopic appearance

Microscopically nuchal fibromas show the following  features :

  • infiltrative growth pattern, rarely invading the underlying bone
  • storiform or fascicular growth pattern
  • variably collagenous or myxoid stroma with accentuated microvasculature
  • loosely distributed bland spindled or stellate fibroblasts
  • rare mitotic activity
  • no necrosis
  • no nuclear pleomorphism
Immunohistochemistry

On immunohistochemistry stains, tumor cells usually express CD34, CD99 and vimentin. Occasional positivity of epithelial membrane antigen and smooth muscle actin is seen. A loss of RB1 expression can be observed .

Genetics

There have been reports of RB1 gene deletion.

Radiographic features

Plain radiograph

Acral fibromyxomas might cause erosive or osteolytic changes on the underlying bone but usually do not feature calcifications .

Ultrasound

On ultrasound, they have been reported as a nodular hypoechoic inhomogeneous lesion with variable vascularity .

MRI

The appearance has been reported as lobulated soft tissue mass in the subungual area .

Signal characteristics
  • T1: isointense to muscle
  • T2: hyperintense
  • STIR:  hyperintense
  • T1 C+ (Gd): heterogeneous enhancement

Radiology report

The radiological report should include a description of the following:

  • location and size of the tumor
  • relation to the underlying bone

Treatment and prognosis

The treatment of choice is surgical excision. Local recurrence can happen in up to one-fourth of the cases, but are non-destructive and can be cured by re-excision. There are no reported metastases .

History and etymology

The first description of acral myxofibroma was done by Fetsch and colleagues in 2001 .

Differential diagnosis

The differential diagnosis of acral myxofibroma includes the following :