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.
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Terminology
The term 'cellular digital fibroma' is not recommended 1,2.
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 1,3,4.
Diagnosis
The diagnosis of acral fibromyxoma is based on the location and histological features of lesion 1.
Diagnostic criteria
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
Clinical presentation
They are slowly enlarging tumors and might be associated with nail deformity They can be painless or painful 1.
Associations
Associations with trauma have been described in rare cases 4.
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 patterns 1,3.
Etiology
The etiology of acral fibromyxoma is unknown 1.
Location
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.
Macroscopic appearance
Macroscopically acral fibromyxomas have a verrucoid or polypoid or lobulated appearance. They have poorly defined borders and a soft to firm consistency 1,3.
Microscopic appearance
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
Immunophenotype
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.
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 1,4,6.
Ultrasound
On ultrasound, they have been reported as nodular hypoechoic inhomogeneous lesions with variable vascularity 4,7.
MRI
The appearance has been reported as lobulated soft tissue mass in the subungual area 4,6.
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 1,3,4,6.
History and etymology
Superficial acral myxofibroma has been first described by the American pathologists John F. Fetsch, William B. Laskin and Markku Miettinen in 2001 5,8.
Differential diagnosis
The differential diagnosis of acral myxofibroma includes the following 2,3:
ingrowing nail
cellular digital fibroma
acral fibrokeratoma
fibrous histiocytoma
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