Pelvic floor dysfunction is characterized by bladder, bowel, or sexual dysfunction with a variable combination of pelvic organ prolapse. It affects multiparous women more commonly than men. Obstetric damage to pelvic floor structures like ilio-coccygeus muscle, pubo-coccygeus muscle, anal sphincter, endopelvic fascia, and pudendal nerve is believed to cause pelvic floor dysfunction in multiparous women. Obstructed defecation syndrome (ODS) constitutes a unique set of chronically constipated patients who fail to completely evacuate their rectum. These patients resort to excessive straining and digital maneuvering of rectum to attain complete rectal evacuation. ODS can result either from a functional abnormality or organic ano-rectal abnormality. Patients with functional abnormality can be treated with bio feedback therapy or psychotherapy, whereas those with an organic ano-rectal disorder respond to surgical correction [5]. The diagnostic armamentarium chiefly consists of fluoroscopic defecography and magnetic resonance defecography (MRD) [5,6,7]. MRD has the capability of demonstrating the various pelvic floor abnormalities with great accuracy. MRD serves as a one stop shop for studying the normal pelvic anatomy and the complete range of pelvic floor abnormalities. MRD lacks radiation exposure. MRD can be performed in sitting position using open configuration MRI or in supine position using closed configuration magnet [7]. MRD performed in supine position yields comparable results to that performed in sitting position for the reason that the straining forces applied during defecation are of sufficient magnitude to elicit the various pathologies [8, 9].
Pelvic floor is divided into three compartments: anterior compartment comprises of bladder and urethra, middle compartment comprises of uterus and vagina, and the posterior compartment is comprised of ano-rectal canal [9, 10]. However, all the three compartments work in unison, and combined disorders of pelvic floor are common and should be assessed simultaneously. Normal ano-rectal angle measures between 108° and 127° [11, 12]. During normal defecation, the pubo-rectalis sling relaxes leading to widening of the ano-rectal angle by 15–20° so that the rectum and anal canal are aligned in a straight line to allow expulsion of fecal matter [13, 14]. Failure of widening of ano-rectal angle during defecation with persistence of acute ano-rectal angle forms the basis for the diagnosis of spastic perineum syndrome (SPS) (Fig. 2) (Video 1). This disorder is also called as paradoxical pubo-rectalis syndrome (PPS). It results from failure of pubo-rectalis muscle to relax during defecation. In fact, there is paradoxical contraction of this muscle during defecation which prevents opening of ano-rectal angle during defecation with consequent failure of evacuation of feces. Thickening of pubo-rectalis muscle has been reported previously in literature in PPS patients [12]. However, Liu et.al in their study concluded that though mean thickness of the pubo-rectalis muscle was more in patients with PPS than in patients without PPS, but the difference between groups was not statistically significant [15]. However, they reported a significant difference in apparent diffusion co-efficient (ADC) values of pubo-rectalis muscle between patients with PPS and patients without PPS which points to the fact that alteration in muscle microstructure might be the underlying mechanism for PPS [15]. Ano-rectal junction descent was the commonest abnormality encountered with 273 (90.3%) patients demonstrating various grades of ano-rectal junction descent (Fig. 3). Descent of ano-rectal junction can occur in isolation but frequently descent of the anterior, and middle compartment structures are also seen in association with it. This is frequently associated with feeling of incomplete evacuation resulting in further increase in straining during defecation and consequent neuropathic injury that may result in incontinence [12]. Anterior rectocele was second commonest abnormality observed in 232 (76.8%) (Fig. 4). Factors that increase the likelihood of developing a rectocele include birth trauma, hysterectomy, chronically increased intra-abdominal pressure, and increased age. Rectoceles assume clinical relevance when symptoms develop as they are responsible for obstructed defecation which usually requires vaginal or perineal digitations to attain rectal emptying [12]. Post defecation retention of jelly within rectocele fairly correlates with patient symptoms and is an important abnormality which usually necessitates digitization (Fig. 5b). Rectal intussusception is classified into mucosal intussusception or full thickness intussusception (Fig. 3d) (Video 2). This causes obstruction to the passage of feces. MR defecography is advantageous in discriminating between mucosal intussusception and full-thickness intussusception and is relevant in treatment planning. Mucosal intussusception can be treated with transanal excision of the redundant or prolapsing mucosa, whereas a rectopexy might be required for full-thickness intussusception [12]. Enterocele, defined as caudal displacement of small bowel loops into the recto-vesical or recto-vaginal space, occurs more commonly in patients who have undergone hysterectomy owing to disruption of pubo-cervical and recto-vaginal portions of supporting endopelvic fascia. Enteroceles are more clearly demonstrable towards the end of defecation process because a fully loaded rectum does not allow sufficient space for descent of small bowel into pelvis [12, 16, 17]. It is vital to detect enterocele because it forms a contraindication for stapled transanal rectal resection (STARR) due to the potential danger to the herniated small bowel during this surgery [11, 18]. Abnormal caudal descent of bladder and cervix below pubo-coccygeal line is also graded into mild, moderate, and severe (Fig. 5a). Abnormal pelvic floor descent grading can be easily remembered by the rule of 3 with descent of an organ below PCL by ≤ 3 cm mild descent, 3–6 cm moderate descent, and > 6 cm severe descent [8, 12, 13]. Defecation phase puts the maximum downward force on pelvic floor which helps in demonstration of a higher number of pelvic organ descents when compared to strain phase [15, 19]. Ano-rectal junction descent was visible in 101 (36.9%) patients on strain phase which increased to 273 in defecation phase. Thus, defecation phase clearly has higher detection rate for ano-rectal junction descent [20]. Similarly, bladder and cervical descent were seen in 16 and 32 patients during strain phase and in 92 and 78 patients respectively during defecation or drain out phase. Defecation phase also identified an additional number 81 (34.9%) rectoceles when compared to strain phase. None of the patients showed intussusceptions during strain, and all the 93 patients of intussusception were identified during defecation phase. Also, we noted that the maximum depth or degree of an abnormality was visible during defecation phase (Fig. 4c, d). So clearly, the diagnostic yield of defecation phase is best among all the phases of defecation and this attests to the fact that defecation phase is the single most important phase to elicit the full range of pelvic floor abnormalities and must be included in magnetic resonance defecography (Video 3 and Video 4). This comes at a slightly higher cost of providing the patient with waterproof diaper and having to explain the patient to defecate on MRI table which might be little embarrassing to many patients.
