Solitary superficial angiomyxoma: an infrequent but distinct soft tissue tumor

Superficial angiomyxoma (SA) is a distinct soft tissue tumor characterized by a circumscribed collection of spindled and stellate fibroblasts that are admixed with thin‐walled blood vessels and embedded in a mucinous stroma. Because of its relative infrequent occurrence, the purpose of this article was to present a classical example of an isolated superficial angiomyxoma and discuss the differential diagnosis.

Superficial angiomyxoma (SA) is a distinct type of soft tissue myxoma characterized by increased numbers of stellate fibroblasts and thin-walled blood vessels admixed with a variable inflammatory infiltrate. Approximately 30% of lesions additionally contain an entrapped epithelial component consisting of keratin cysts or thin strands of squamous epithelium. Despite the fact that 20-30% of lesions recur, metastases have yet to be described. [1][2][3] Because of its relative infrequent occurrence, the purpose of this article was to present a classical example of an isolated superficial angiomyxoma and discuss the differential diagnosis.
Case report A 35-year-old African American man presented with a slowly enlarging asymptomatic nodule on his midback treated 9 months previously with liquid nitrogen and again 1 month later. The patient had no history of endocrine abnormalities, lentigines, blue nevi or other neoplasms. On examination, a soft 1-cm well-demarcated pedunculated nodule was noted (Fig. 1).
Histological evaluation of a shave biopsy revealed a dome-shaped lesion containing stellate and multinucleated fibroblasts admixed with numerous small thin-walled blood vessels surrounded by pools of mucin that formed cleft-like spaces (Fig. 2). Lymphocytes were scattered throughout the lesion, and centrally, an abortive follicular structure was appreciated. There was no evidence of epidermal effacement, dermal fibrosis or neovascularization suggestive of the prior treatment. Immunohistochemical stains showed strong labeling of the stellate cells with CD68 and factor XIIIa, but CD34 only labeled the blood vessels ( Fig. 3A-C). To date, there is no evidence of recurrence after complete excision.

Discussion
Allan depicted SA as a specific entity in 1988; however, similar tumors had been previously described, albeit by different names, at least 30 years earlier. 3 Originally proposed to be synonymous with cutaneous focal mucinosis, myxoid perifollicular fibroma, fibrofolliculomas, trichofolliculomas and trichodiscomas, Calonje et al. 3 disagreed with this hypothesis concluding that SA was a distinct entity. 2 SA has a slight male predilection, typically presenting between the ages of 20-40 years. Although they preferentially occur on the trunk, extremities and head and neck regions, they can arise in a variety of anatomic locations. [1][2][3][4][5] The majority of lesions occur in isolation; however, multiple SA, especially those located on the external ear, are considered pathognomonic for Carney complex, an autosomal dominant disorder associated with multiple myxomas (cardiac, cutaneous and mammary), blue nevi, lentigines, psammomatous melanotic schwannoma and endocrine overactivity. [1][2][3][4] Although the exact incidence is unknown, in the index article, only 27 solitary tumors were identified among 4500 consults seen over 23 years. 2 To evaluate the incidence at our institution, a Systematized Nomenclature of Medicine (SNOMED) word search engine using the descriptors myxoma, angiomyxoma and superficial cutaneous angiomyxoma was performed within the computerized archives of the    Department of Pathology, Naval Medical Center San Diego. Over the past 10 years, approximately 180,000 surgical pathology cases were examined and only two cases, other than the one that is the subject of this article, were identified. Because our population is somewhat skewed, several other dermatopathologists at various institutes were queried, and SA represented approximately 0.0008% (14/1,680,000) of all specimens accessioned. Of the two soft tissue pathologists questioned, SA represented less than 0.3% (175/ 59,500) of all soft tissue neoplasms; therefore, SA is infrequently encountered in routine practice. The differential diagnosis of SA is extensive; nevertheless, the most common benign neoplasms include intramuscular myxoma, juxta-articular myxoma, aggressive angiomyxoma, angiomyofibroblastoma, superficial acral fibromyxoma and nerve sheath myxoma. [1][2][3][4][5] While clinical and histological overlap exists among these entities, they are readily differentiated by characteristic clinicopathological findings (Tables 1 and 2). [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Other benign entities with extensive mucinous stroma include ganglion cysts, focal mucinosis, myxoid neurofibroma and angiomyxolipoma. 3,5 Lastly, a few malignant myxomatous tumors should be included in the differential diagnosis, particularly with large lesions that extend deep, namely myxofibrosarcoma, fibromyxoid sarcoma, myxoid liposarcoma, myxoid dermatofibrosarcoma protuberans and myxoid malignant peripheral nerve sheath tumor. 1,3,5 Almost all reported cases that have utilized immunohistochemical stains have been immunoreactive with vimentin and negative with desmin and cytokeratin. 3,5,[10][11][12][13][14][15][16] The staining results for CD34, smooth muscle actin, muscle-specific actin, S-100 and factor XIIIA have been more variable. The case presented herein had a slightly different immunophenotype compared with previously reported cases. Although the spindled and multinucleated cells strongly labeled with factor XIIIA, a finding reported in approximately 53% of cases that have utilized this stain, 5,10,12,13,15 these cells failed to stain with CD34, which has been expressed in approximately 71% of cases. 5,10-16 Furthermore, the lesion strongly expressed CD68, a finding that has not been previously reported. However, since the use of CD68 has been infrequently reported in the literature, 12,13 the positive staining of the current case may not be unique and requires further investigation.
In conclusion, the features most useful to differentiate a SA from other myxoid tumors include its superficial location, lack of atypia, stromal inflamma-