Acral fibromyxomas are benign mesenchymal proliferations prone to recurrence usually found in the subungual and periungual sites of the digits.
Superficial acral fibromyxoma or digital fibromyxoma are other acceptable names, the term cellular digital fibroma is no longer recommended 1.
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.
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 3.
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 1,2.
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. In rare occasions, they might be seen in other areas of the extremities as hands and feet ankles, wrists or lower legs and thighs 1-3.
Macroscopically acral fibromyxomas have a verrucoid or polypoid or lobulated appearance. They have poorly defined borders and a soft to firm consistency 1,2.
Microscopically nuchal fibromas show the following features 1-3:
- 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 1-5.
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 1,3,4.
On ultrasound, they have been reported as a nodular hypoechoic inhomogeneous lesion with variable vascularity 3,5.
The appearance has been reported as lobulated soft tissue mass in the subungual area 3,4.
- 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
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 1-4.
History and etymology
The first description of acral myxofibroma was done by Fetsch and colleagues in 2001 6.
The differential diagnosis of acral myxofibroma includes the following 2:
- 1. W.H.O. Classification WHO Classification of Tumours Editorial Board, Who Classification of Tumours Editorial. Soft Tissue and Bone Tumours. (2020) ISBN: 9789283245025
- 2. Ashby-Richardson H, Rogers GS, Stadecker MJ. Superficial acral fibromyxoma: an overview. (2011) Archives of pathology & laboratory medicine. 135 (8): 1064-6. doi:10.5858/2009-0684-RSR1 - Pubmed
- 3. Crepaldi BE, Soares RD, Silveira FD, Taira RI, Hirakawa CK, Matsumoto MH. Superficial Acral Fibromyxoma: Literature Review. (2019) Revista brasileira de ortopedia. 54 (5): 491-496. doi:10.1016/j.rbo.2017.10.011 - Pubmed
- 4. Grigore LE, Baican CI, Botar-Jid C, Rogojan L, Letca AF, Ungureanu L, Cosgarea R. Clinico-pathologic, dermoscopic and ultrasound examination of a rare acral tumour involving the nail - case report and review of the literature. (2016) Clujul medical (1957). 89 (1): 160-4. doi:10.15386/cjmed-517 - Pubmed
- 5. Bindra J, Doherty M, Hunter JC. Superficial acral fibromyxoma. (2012) Radiology case reports. 7 (3): 751. doi:10.2484/rcr.v7i3.751 - Pubmed
- 6. Fetsch JF, Laskin WB, Miettinen M. Superficial acral fibromyxoma: a clinicopathologic and immunohistochemical analysis of 37 cases of a distinctive soft tissue tumor with a predilection for the fingers and toes. (2001) Human pathology. 32 (7): 704-14. doi:10.1053/hupa.2001.25903 - Pubmed