Imaging description

Perineal wound complications are a substantial source of morbidity after major perineal surgery such as abdominoperineal resection or pelvic exenteration [1]. A variety of muscular interposition flaps, including rectus abdominis, gracilis, and gluteus maximus, can be used to help in the reconstruction of the perineum after such surgery in order to reduce these complications [1–3]. Other uses of perineal myocutaneous flaps include formation of a neovagina or replacement of the anal sphincter [4–6]. Imaging findings vary with the type of flap. In general, the transposed muscle appears as a bandlike soft-tissue density mass, abutting the pelvic side wall or sacrum (Figure 91.1). Transposed subcutaneous adipose tissue may be seen as a fat density mass within the perineum (Figure 91.2). Transposed skin, if harvested to form a neovagina, may be seen as linear soft-tissue density surrounded by fat posterior to the symphysis pubis. When the rectus abdominis is used, the donor site can be identified by unilateral thinning of the rectus sheath. Findings of complications may also be seen, including flap necrosis, infection, fistula, muscle atrophy, or tumor recurrence [4,5].

Importance

This pseudotumor is most problematic in patients who have had perineal surgery for malignancy, since in this setting the pseudomass created by the transposed muscle may be mistaken for recurrent cancer.

Typical clinical scenario

The two main indications for perineal muscle flap transposition are reconstruction after pelvic exenteration for recurrent gynecologic malignancy or reconstruction after abdominoperineal resection for anorectal cancer.