Superficial Angiomyxoma of the Wrist: Case Report and Literature Review

Abstract

Background/Aim: Superficial angiomyxoma (SAM) is a rare benign soft-tissue tumor that usually occurs in the trunk, head and neck, and lower extremity of middle-aged adults. Herein, we describe an unusual case of SAM of the wrist, which was initially diagnosed as a ganglion cyst on imaging.

Case Report: The patient was a 71-year-old man with no history of trauma who presented with a 2-year history of a palpable mass in the left wrist. Physical examination revealed a 2.5-cm, elastic hard, mobile, nontender mass. Magnetic resonance imaging revealed a well-defined mass with iso-signal intensity relative to skeletal muscle on T1-weighted sequences and very high signal intensity on T2-weighted fat-suppressed sequences. Subtle internal enhancement was seen following gadolinium administration. Complete excision was performed under general anesthesia with tourniquet control. Histologically, the lesion was composed of bland spindle to stellate-shaped cells in an abundant myxoid stroma. Immunohistochemically, the lesional cells were positive for CD34 but negative for S-100 protein, smooth-muscle actin, desmin, epithelial membrane antigen and pancytokeratin. These findings were consistent with a diagnosis of SAM. There was no clinical evidence of recurrence during a follow-up period of 3 months.

Conclusion: Although extremely rare, SAM should be considered in the differential diagnosis of a cyst-like solid lesion near small joints.

Superficial angiomyxoma (SAM), also known as cutaneous myxoma, is a rare benign soft-tissue tumor that may be sporadic or arise in association with Carney complex. It usually presents as a slow-growing polypoid or papulonodular lesion in the superficial tissues of the trunk, head and neck, and lower extremity. SAM may occur at any age but has a peak incidence in the fourth and fifth decade of life (1-3). The lesion usually measures 1 to 5 cm in diameter (1,2). Complete excision is the treatment of choice, but local recurrence is seen in 3.6-38.1% of cases (1-3). There is no metastatic potential and no reports of malignant transformation.

The differential diagnosis of myxoid soft-tissue tumor is broad, including both benign and malignant conditions (4-7). Herein, we present an unusual case of SAM of the wrist, mimicking a ganglion cyst. We also provide a literature review about the clinicopathological and imaging features of SAM. Written informed consent was obtained from the patient to publish this case report and accompanying images.

Case Report

A 71-year-old man presented with a 2-year history of a slow-growing, painless mass in the dorsal aspect of the left wrist. He had no history of wrist trauma. Physical examination showed a 2.5-cm, elastic hard, mobile, nontender mass. The range of motion of the affected wrist was normal. Neurological and vascular examinations were unremarkable. Plain radiographs revealed a noncalcified soft-tissue swelling on the dorsal aspect of the wrist. Magnetic resonance imaging showed a subcutaneous soft-tissue mass with isointense signal relative to skeletal muscle on T1-weighted sequences (Figure 1A) and very high signal intensity on T2-weighted fat-suppressed sequences (Figure 1B). Contrast-enhanced fat-suppressed T1-weighted sequences (Figure 1C) showed subtle internal enhancement of the mass. Our preoperative diagnosis was a ganglion cyst.

Figure 1. Axial magnetic resonance images of superficial angiomyxoma in the left wrist. The mass showed an isointense signal relative to skeletal muscle on T1-weighted sequence (A) and very high signal intensity on T2-weighted fat-suppressed sequence (B). Contrast-enhanced fat-suppressed T1-weighted sequence (C) demonstrated subtle internal enhancement of the mass.

The operative procedure was performed under general anesthesia with pneumatic tourniquet control and loupe magnification. A longitudinal skin incision was made over the mass. The mass was easily seen under the subcutaneous tissue and was completely excised. Microscopically, the lesion was composed of bland spindle to stellate-shaped cells in a prominent myxoid stroma with a thin arborizing vascular network (Figure 2A). Atypical mitoses and necrosis were not present. Immunohistochemically, the lesional cells were positive for CD34 (Figure 2B). Staining for S-100 protein, smooth-muscle actin (SMA), desmin, epithelial membrane antigen (EMA) and pancytokeratin was negative. The Ki-67 labelling index was 3%. Based on these findings, the lesion was diagnosed as a SAM.

Figure 2. Histological and immunohistochemical findings of superficial angiomyxoma. The tumor was composed of bland spindle to stellateshaped cells in an abundant myxoid stroma with small, thin-walled, curvilinear vessels (A) (hematoxylin and eosin staining). The tumor cells were immunohistochemically positive for CD34 (B). Original magnification, ×100; bar=100 μm.

The postoperative course was uneventful. There was no clinical evidence of recurrence during a follow-up period of 3 months.

Discussion

SAM, first properly described by Allen et al. in 1988 (1), is characterized by distinctive histological features with loss of expression of protein kinase A regulatory subunit 1 alpha (PRKAR1A) (8). SAM behaves in a benign manner although its exact etiology is unknown. This case report illustrates that SAM can be included in the differential diagnosis of a myxoid mass of the wrist joint.

There is scant literature on the radiologic appearance of SAM (9-11). The best imaging modality for evaluating SAM is magnetic resonance imaging because of its excellent tissue contrast. On T1-weighted images, the lesion is usually of low to intermediate signal intensity. On T2-weighted images, the lesion typically demonstrates very high signal intensity, probably related to the high water content. Inhomogeneous enhancement is seen following contrast administration. In our case, however, internal or nodular enhancement was hardly seen. On the other hand, intramuscular myxoma is the most common benign myxoid neoplasm and reveals low to intermediate signal intensity on T1-weighted images and markedly high signal intensity on T2-weighted images. Following contrast administration, the lesion usually shows heterogeneous internal enhancement with/without peripheral enhancement with occasional fine internal septa (12). We therefore suggest that the magnetic resonance appearance of SAM is similar to that of intramuscular myxoma.

The definitive diagnosis of SAM is made after excision and histopathological analysis. Histologically, SAM usually presents as a proliferation of spindle to stellate-shaped cells in a prominent myxoid stroma with a thin arborizing vascular network. Nuclear atypia and mitotic activity are generally absent (3). By immunohistochemistry, the tumor cells are positive for vimentin and CD34 (3). S-100 protein, SMA, desmin, EMA and pancytokeratin are typically negative (2,3). Our case was in concordance with previous results in this regard. Recently, Neumann et al. reported that loss of PRKAR1A was seen in 55.2% of cases (8). Unlike SAM, PRKAR1A was retained in other histological mimics, including superficial acral fibromyxoma, digital mucous cyst, myxofibrosarcoma and myxoid dermatofibrosarcoma protuberans (8). Therefore, the use of PRKAR1A immunostaining is a valuable adjunct in the diagnosis of SAM, particularly in small biopsy specimens.

In the current case, the differential diagnosis includes juxta-articular myxoma (JAM). This usually presents as a slowly enlarging mass in the vicinity of large joints, particularly the knee. JAM can occur at any age but has a peak incidence in the fifth and sixth decade of life, with a male predominance (13). Local recurrence following surgery is not uncommon, occurring in about one-third of cases (14). Histologically, JAM is generally hypocellular and composed of bland spindle-shaped cells in a hypovascular myxoid stroma. JAM has histological features similar to those of SAM, but there are certain clinical and histological differences between these two lesions. Unlike SAM, JAM is rarely found in the trunk or head and neck and is frequently associated with prominent cystic changes (14).

In conclusion, we described an unusual case of SAM mimicking a ganglion cyst on imaging. SAM should be considered in the differential diagnosis of a cyst-like, myxoid soft-tissue neoplasm of the wrist.

Conflicts of Interest

The Authors declare no conflicts of interest associated with this article.

Authors’ Contributions

YC provided direct patient care and drafted the article. JN performed the operation and supervised the research. TN reviewed the article. All Authors read and approved the final article.

Acknowledgements

This study was supported in part by the Japan Society for the Promotion of Science KAKENHI (21K09336).