Rectocele is defined as an outpouching or bulging of the anterior rectal wall that develops during defecation. It is observed in most parous women (78–99%) but is rarely seen in men. The underlying etiology of a rectocele is weakening of the support structures of the pelvic floor, particularly of the rectovaginal fascia [29]. Several factors may increase the risk of developing a rectocele, such as vaginal birth trauma (multiple, difficult, or prolonged deliveries; forceps delivery; perineal tears), constipation with chronically increased intra-abdominal pressure, hysterectomy, aging, and congenital or inherited weaknesses of the pelvic floor support system [29].

Most rectoceles develop anteriorly due to weakness of the structures sustaining the anterior rectal wall. A rectocele rarely develops posterolaterally; in this case, the lesion — a posterior perineal hernia — occurs laterally through a puborectalis muscle defect rather than in the midline [6–8, 29]. Rectal invagination is frequently associated with rectoceles [6–8, 21, 29]. Anterior rectoceles are specifically associated with rectal wall invagination and infolding of the posterior rectal wall. Rectoceles are also frequently associated with enteroceles and anismus; enteroceles or peritoneoceles may act as compensatory dysfunctions, improving evacuation from the rectocele and reducing fecal trapping.

Symptoms related to rectocele may be primarily vaginal (bulging, dyspareunia) or rectal (defecatory dysfunction, constipation, and sensation of incomplete evacuation). Fecal trapping in the rectocele leads many patients to empty it by digitating and pressing on the posterior wall of the vagina or perineum.

Sensitivity of the clinical examination in rectocele diagnosis varies from 31% to 80% [3, 4, 29] and is generally unable to distinguish an enterocele from a high rectocele. For these reasons, dynamic MRI during maximal straining and/or evacuation is clinically useful to identify and grade rectoceles (Fig. 3). Clinically relevant symptomatic rectoceles >3 cm are easily detected at supine MR defecography and DPF-MRI (Figs. 1–4). Rectoceles <2 cm are considered normal features in most parous women rather than clinically relevant features [6–8, 29]. At MRI, a rectocele is measured during the phase of maximal straining and evacuation as the distance between anal midline and the anterior rectal wall or as the depth of wall protrusion beyond the expected anterior rectal wall. At MRI, rectoceles are graded as small if <2cm, mild as being between 2 and 4 cm, and large if >4 cm [7, 19]. By using this staging system, MRI sensitivity in detecting large rectoceles (>3.5 cm) ranges between 87% and 100% [19, 20].

Rectal intussusception is invagination of the rectal wall [6–8, 29] located either anteriorly, posteriorly, or circumferentially, and may involve the full thickness of the rectal wall or the mucosa only. Rectal intussusception is classified as intrarectal if it remains within the rectum, intra-anal if it extends inside the anal canal, or extra-anal if it passes the anal sphincter; the latter is also called complete or full rectal prolapse [18, 19]. Rectal intussusception is unlikely to obstruct defecation, but it can cause a sensation of incomplete emptying. If the invagination progresses becoming intra-anal, patients most likely experience a sensation of incomplete defecation due to outlet obstruction. Invagination may also cause sequestration of a rectocele, with contents returning into the rectum during relaxation, thus resulting in incomplete evacuation and OD as well (Figs. 2 and 4).