Acral fibromyxoma

Last revised by Dr Joachim Feger on 14 Sep 2022

Acral fibromyxomas, also known as superficial acral fibromyxomas or digital fibromyxomas are benign mesenchymal proliferations prone to recurrence usually found in the subungual and periungual sites of the digits.

The term 'cellular digital fibroma' is not recommended 1,2.

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 1,3,4.

The diagnosis of acral fibromyxoma is based on the location and histological features of lesion 1.

Diagnostic criteria according to the WHO classification of tumors: soft tissue and bone (5th edition) 1:

  • acral or for the most part periungual location
  • dermal tumor with infiltration of the subcutis
  • lobulated structure with fascicular, whorled or storiform growth pattern
  • bland spindle cells in a collagenous or variably myxoid stroma

The following immunohistochemical criteria are desirable:

  • CD34 positivity
  • loss of RB1 expression

They are slowly enlarging tumors and might be associated with nail deformity They can be painless or painful 1.

Associations with trauma have been described in rare cases 4.

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 patterns 1,3.

The etiology of acral fibromyxoma is unknown 1.

Acral fibromyxomas are usually found in an acral periungual and subungual location of the fingers and toes. On rare occasions, they might be seen in other areas of the extremities such as hands and feet ankles, wrists or lower legs and thighs 1,3-5.

Macroscopically acral fibromyxomas have a verrucoid or polypoid or lobulated appearance. They have poorly defined borders and a soft to firm consistency 1,3.

Microscopically nuchal fibromas show the following  features 1,3-5:

  • 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

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 1, 3-6.

There have been reports of RB1 gene deletion.

Acral fibromyxomas might cause erosive or osteolytic changes on the underlying bone but usually do not feature calcifications 1,4,6.

On ultrasound, they have been reported as nodular hypoechoic inhomogeneous lesions with variable vascularity 4,7.

The appearance has been reported as lobulated soft tissue mass in the subungual area 4,6.

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

The radiological report should include a description of the following:

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

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 1,3,4,6.

Superficial acral myxofibroma has been first described by the American pathologists John F. Fetsch, William B. Laskin and Markku Miettinen in 2001 5,8.

The differential diagnosis of acral myxofibroma includes the following 2,3:

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Cases and figures

  • Case 1
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