Several lesions are characterized by an abundant myxoid matrix and a paucity of spindle-shaped stromal cells. Virchow first introduced the term myxoma in 1863, describing a benign tumor which histologically resembles the mucinous substance of the umbilical cord (2, 3). It was Stout in 1948, however, who established myxoma as a distinctive lesion, in a comprehensive report of 49 cases from the Laboratory of Surgical Pathology of Columbia University and 93 additional cases from the literature (exclusive of those within the heart) (4). Although only four (3%) of the lesions in Stout’s original report were intramuscular, the intramuscular myxoma is the best known of these myxoid lesions to radiologists and the one most likely to mimic a myxoid musculoskeletal sarcoma (5, 6, 7, 8). A subsequent report of almost 200 myxomas of various sites from the Armed Forces Institute of Pathology (AFIP), Washington, DC, identified 34 (17%) as intramuscular in origin (9). The reported annual incidence is one case per million people (5, 6, 7, 8). Other locations of noncardiac myxoma, in decreasing order of frequency, include subcutaneous and aponeurotic tissue (22%), bone (18%), genitourinary tract (16%), and skin (15%) (9). The more recent study of 45 cases by Murphey et al. likely reflects the distribution of lesions seen by radiologists more accurately, showing that 82% of musculoskeletal myxomas were intramuscular, 9% intermuscular, and 9% subcutaneous; three of these cases were also juxta-articular (10).

The term aggressive angiomyxoma was use by Steeper and Rosai in 1983 (56) to describe a distinct myxoid
neoplasm characteristically occurring in the perineal and pelvic regions of adult women (5, 56). The WHO recognized this lesion as deep aggressive angiomyxoma (6). It occurs most commonly in women in their third to sixth decade of life (peak incidence in the fourth decade), with a female-to-male ratio of more than 6:1 (5, 6, 7, 57, 58, 59). Common locations include the pelvicoperineal and retroperitoneal regions (5, 6, 7, 59). In men, the tumor involves analogous sites including the scrotum and inguinal area (60, 61). Aggressive angiomyxoma may be asymptomatic or cause pain and dyspareunia. Lesions may be mistaken for a Bartholin cyst because of their location. Tumors have been reported during pregnancy, and tumor growth during pregnancy and their prevalence in women’s reproductive years suggests that these lesions are hormone-dependent (62, 63).

At gross pathologic evaluation, deep aggressive angiomyxomas are often quite large (10 to 20 cm in size), lobulated, partially circumscribed, gelatinous masses (5, 6, 7, 59). Microscopically, deep aggressive angiomyxomas are low to moderate in cellularity and composed of small, stellate, spindled cells (64). Scattered, dilated vessels of variable size (from capillaries to large vessels) are usually seen in the lesion (65). The vessels are often surrounded by smooth muscle cells. Mitoses are infrequent. Cytogenetic aberrations are seen with rearrangement of 12q14-15 in various translocations (5, 6, 7, 59, 66, 67).

Although wide excision is the treatment of choice for deep angiomyxoma, the large size, infiltration, and location of lesions often precludes complete removal (65, 68, 69). Thus, the local recurrence rate is generally high, ranging from 30% to 100% (5, 6, 7, 59, 65); however, more recent studies have demonstrated much lower rates of local recurrence following aggressive surgical excision (70, 71). Local recurrence is often adequately treated by reexcision alone, without the need of adjunct therapy (65). Deep aggressive angiomyxoma is generally considered to have no significant metastatic potential and documented metastases are exceedingly rare (72, 73).

Radiographs are usually normal or show a nonspecific soft tissue mass with displacement of pelvic structures. Angiography typically reveals a hypervascular mass, whereas sonography demonstrates a heterogeneous, hypoechoic, soft tissue mass (74, 75, 76, 77, 78). Internal echogenic septa, cystic areas, and a hyperechoic rim are also described (Fig. 11.10).

CT shows a well-defined mass with attenuation lower than that of muscle (Fig. 11.11) (60, 74, 76, 77, 78, 79). On T1-weighted MR images, deep aggressive angiomyxoma is usually low to intermediate in signal intensity (60, 76, 78, 79, 80). On T2-weighted MR images, these lesions reveal intermediate-to-high signal intensity, likely because of the high water content seen histologically (Figs. 11.10 and 11.11) (76, 79, 80). Deep aggressive angiomyxoma is described as having a characteristic swirled or layered appearance on CT and MR imaging (Figs. 11.10 and 11.11). This appearance (83% of cases by CT or MR imaging) is seen on T2-weighted MR imaging and post-contrast CT or MR images. In the study by Outwater et al. (79), the strands of tissue creating this swirled architecture were often best seen on contrastenhanced CT or MR imaging, and were mildly lower signal intensity on long TR images. Cross-sectional imaging, particularly CT or MR imaging, reveals the effect of these often large masses on surrounding pelvic structures and whether or not the tumor traverses the pelvic diaphragm; anatomic features that are essential in planning surgical resection.

Myothelioma and mixed tumor of soft tissue are currently grouped together by the WHO because of their morphological and immunophenotypical similarity (81, 82, 83, 84). Myoepithelioma is composed exclusively (or predominantly) of myoepithelial cells while mixed tumors show ductal differentiation (84). About 10% of myoepitheliomas will contain a ductal component and
are then termed mixed tumor (84). Mixed tumor of soft tissue is analogous to the chondroid syringoma described in dermatopathology (Chapter 12). Lesions with large epithelioid cells showing cytoplasmic vacuolation are termed parachordoma, now considered a morphologic variant of mixed tumor/myoepithelioma (81, 84), with the designation of parachordoma used to emphasize its morphological similarities to axial chordoma (85). Malignant myoepithelial neoplasms are designated myoepithelial carcinoma (84).

Adults are typically affected in the fourth to sixth decade of life, with an average of 35 years of age (6, 7, 82, 83). However, as with many neoplasms, there is a wide age range, and 20% of patients are children younger than 10 years (6, 7, 82, 83, 86). A mild male predilection is reported in some series (6, 7, 82, 83, 87). Sites of involvement are most frequently the subcutaneous or deep subfascial soft tissues of the extremities (11, 12, 74, 75). The upper extremity is more commonly affected than the lower extremity. Other involved locations include the head/neck, trunk, and rarely, bone (11, 12, 74, 75). Clinically, patients present with a nonspecific painless swelling or mass.