A rare clinical presentation of pedunculated superficial angiomyxoma in the anal canal: A case report

Abstract

Superficial angiomyxoma is an infrequent benign soft tissue tumor, clinically presented as slow-growing, painless cutaneous, or subcutaneous mass. It is mostly described in middle aged population with preference location in trunk, head, neck, and genitalia. Herein, we report a rare growth variant of a solitary superficial angiomyxoma with uncommon site of occurrence in a 39-year-old female. Pedunculated superficial angiomyxoma originating in anal canal is extremely rare. Histological features of the lesion comprising of spindle-shaped and stellate cells dispersed in myxoid stroma and prominent thin-walled blood vessels defined the diagnosis of superficial angiomyxoma. Tumor cells with immunohistochemistry analysis showed positivity for vimentin and CD34 and negativity for S100, while Ki-67 showed a low proliferation index. The recurrence of superficial angiomyxoma is previously described, but in our case no signs of recurrence were seen in follow-up for a period of 6 months. Superficial angiomyxoma should be considered as differential diagnosis with other polypoid or nodular masses in anal canal.

Introduction

Superficial angiomyxoma (SAM) is an uncommon benign tumor of cutaneous soft tissue. It occurred at any age range, but more frequently was described in the fourth decade, mean age of 39 years. ¹ Most common lesions were clinically presented as solitary papules, nodules and polypoid masses located in trunk, lower extremity, head, neck, and genitalia.^2,3 Perineal region was among the rarest localizations, while in the literature only one case was reported in anal canal. ⁴ Herein, we present the clinical and histological features of an unusual case of solitary SAM located in the anal canal.

Case presentation

A 39-year-old female presented at the surgical department at Hospital Clinical Center of Kosova with complains about a mass in the anal canal. The mobile anal mass was described as painless, slow growing lesion, attached to the surrounding mucosa by a narrowed pedicle, which prolapses time to time through the anus, causing local irritation, discomfort, and pain when entrapped. After the clinical examination, the lesion was guided as pedunculated anal polyp. Meanwhile, the local surgical excision was done. The mass was completely excised and sent for histopathological examination. Patient medical history and clinical examinations showed no similar changes elsewhere in the body. No medical records about any underlying medical conditions. At gross examination, the tissue specimen was described as a white polypoid lesion, upraised on the narrowed stalk, with the maximal diameter of 3 cm (Figure 1(a)). The outer surface was uneven with superficial small papillary elevations resembling cauliflower. The cut surface was white, translucent, glistening, and gelatinous (Figure 1(b)). Microscopically, the tumor was hypocellular composed of myxoid stroma, dispersed spindle-shaped and stellate cells, and small and medium thin-walled blood vessels. Scattered tumor cells showed scant cytoplasm and fine delicate cytoplasmic extensions (Figure 2(a)). No tumor cell atypia or necrosis was detected. Mixed inflammatory infiltrate was perivasculary distributed, being more pronounced in subepithelial sites. Overlying non-neoplastic stratified squamous epithelium showed reactive changes as focal keratosis, acanthosis, and papillomatosis. The presence of loose hypocellular myxoid stroma was highlighted with alcian blue stain (Figure 2(b)). To further differentiate the lesion, a panel of immunohistochemistry markers such as Vimentin, CD34, and S100 was performed. Diffuse cytoplasmic staining for Vimentin was detected in scattered tumor spindle and stellate cells (Figure 2(c)). Immunostaining with CD34 was more prominent in endothelial cells of blood vessels, and it showed moderate cytoplasmic expression in tumor cells (Figure 2(d)), whereas described cells were negative for S100 (Figure 2(f)). The proliferation index detected by immunostaining with Ki67 was below 4% (Figure 2(e)). The follow-up period of 6 months showed no clinical evidence of recurrence.

Figure 1.

Gross appearance of superficial angiomyxoma: (a) White polypoid mass with superficial papillary elevations (cauliflower-like). (b) The cut surface showing white translucent, glistening appearance.

Figure 2.

Histopathological images: (a) HE image, showing spindle and stellate cells dispersed in myxoid stroma, thin-walled blood vessels and inflammatory cells, concentrated mostly in subepithelial site (original magnification 40×). (b) Alcian blue staining showing hypocellular myxoid stroma (original magnification 40×). (c) Positive expression of Vimentin in tumor cells (original magnification 40×). (d) High expression of CD34 in blood vessels and moderate positive expression in tumor cells (original magnification 40×). (e) Expression of Ki-67 showing a very low proliferation index in tumor cells, and positive reactive expression in epithelia (original magnification 40×). (f) Tumor cells showing negative expression for S100 (original magnification 100×).

Discussion

SAM was first described in 1985 as part of Carney complex, an autosomal dominant syndrome characterized with multiple skin abnormalities, and variety of endocrine and non-endocrine tumors. ⁵ Allen et al. ¹ further defined solitary SAM as a distinct entity of histological superficial soft tissue tumor with myxoid features. Either isolated lesions or associated with Carney complex, SAM global occurrence is reported to be infrequent. In our case, clinical examination and patient history excluded the Carney complex, due to absence of the other associated abnormalities. While the different locations of tumor were described in literature, ⁴ to our knowledge, the current reported case is the second reported case of SAM with anal canal presentation.

There is a list of histologic entities described as the anal polyps, but the most common and relevant ones are fibroepithelial polyps, ⁶ aggressive angiomyxoma, ⁷ and soft tissue tumors with myxoid features.^8,9 Even though the above-mentioned entities are all of benign nature, they have different recurrence rate and proper diagnosis is of paramount clinical importance.

Fibroepithelial polyps are clinically presented as sessile or pedunculated masses of invariable size, often in the background of chronic inflammation. ⁶ Besides their soft consistency, the fleshy appearance of the cutting surface distinguishes from translucent and gelatinous seen in SAMs. ¹⁰ The classic histological features of fibroepithelial polyps are myxoid to collagenous stroma covered by superficial squamous epithelium. ¹⁰ Though the myxoid stroma is reported in cases associated with stromal edema, it was more prominent in the subepithelial region, and over the time, it shifts to more collagenized stroma. ¹¹ Therefore, the clinical aspects and the nature of the stroma are useful morphological features to be considered in the differential diagnosis between two lesions.

Aggressive angiomyxoma is a benign, myxoid, and vascular tumor, often described in perineum and genital tract but usually found deep in soft tissues. ⁷ In addition to sharing some of similar morphological features to SAM, there are certain histological differences. Tumor vascular channels appear to be much larger and thicker associated with hemorrhage areas compared to SAM. ¹² Tumor cells show a mild atypia despite low mitotic rate (Ki-67 below 4%) ¹³ and frequently infiltrate underneath muscle fibers, nerves, and adipose tissue. ⁷ Thus, wide margin resection is mandatory. There are no specific immunohistochemical markers to distinguish superficial from aggressive angiomyxoma.

Additionally, lesions that should be considered in the differential diagnosis are soft tissue tumors with myxoid features like myxoid leiomyoma ⁸ or nerve sheath myxoma. ⁹ Although the lesions are of low frequency, they are rarely described in the anal region. Careful attention should be given to helpful diagnostic clues such as focal myxoid changes, attentive identification of the transitional area between the myxoid features and smooth muscle/nerve sheath differentiation and storiform growth pattern. ⁸ In differential diagnosis with nerve sheath myxoma, a very useful tool is diffuse positive S100 expression. ⁹ In our case, S100 was negative, which is in line with reported data. ⁷ Furthermore, spindle and stellate tumor cells were positive for Vimentin and CD34 markers.

Interestingly, the different range of recurrence was described in SAM, which oscillates between 20% and 40%. ¹⁴ The mean period of recurrence time was 18 months. ¹ Tumors with epithelial components were more prone to recur ¹ as well as those with incomplete resection. ³ The current presented case has not shown any recurrence up-to-date. In case of fibroepithelial polyps, the risk for recurrence is not relevant, while in aggressive angiomyxoma, it doubles (around 71%). ¹⁵ The only suggested treatment for SAM is complete surgical excision. Besides surgical treatment with wide margin, anti-hormonal therapy was an option for cases of aggressive angiomyxoma. ¹²

The pedunculated configuration, recurrence, morphological, and immunohistochemical features, low mitotic rate, as well as the absence of necrosis and atypia in tumor cells, are helpful tools to differentiate the SAM from other tumors with myxoid features.

Conclusion

Pedunculated SAMs clinically mimics the fibroepithelial polyps and may be misdiagnosed.

Herein, we underline the importance of the accurate diagnosis, which is necessary for the appropriate treatment, imperative as prediction tool for local recurrence. The present reported case is indicative that SAM should be highlighted as a differential diagnosis for cutaneous masses in perineal region, especially those localized in the anal canal.