Role of transverse diameter of the rectum in lower urinary tract symptoms and functional constipation in children and adolescents

Aim: Although a correlation has been reported between enlarged rectal diameter and functional constipation (FC), the relevance of measuring the transverse diameter of the rectum for diagnosing FC remains unclear, even in patients with lower urinary tract symptoms (LUTS). This study aimed to measure rectal diameter in children/adolescents diagnosed with LUTS, with and without FC.

Methods: This cross-sectional study included 4-17 years old children/adolescents attending a multidisciplinary outpatient clinic for urinary disorders between June 2016 and November 2018. All participants had LUTS, with or without FC. Those incorrectly completing the study questionnaires or with neurological and/or anatomical abnormalities of the genitourinary and/or gastrointestinal tract were excluded. Urinary symptoms were evaluated using the dysfunctional voiding symptom score and FC was assessed using the Rome IV criteria. Transabdominal ultrasonography was used to evaluate the bladder and measure rectal diameter. A transverse diameter ≥3 cm defined an enlarged rectum. Bladder capacity (i.e. the bladder volume immediately before voiding), post-void residual urine, bladder wall thickness and first volume voided after ultrasonography were measured.

Results: Mean age was 8.9 ± 3.2 years and 55.1% were female. Of 107 patients included, constipation was diagnosed in 72 (67.3%), and lower urinary tract dysfunction in 90 (84.1%). In 72 participants (67.3%), lower urinary tract dysfunction was associated with FC, constituting bladder and bowel dysfunction. Rectal diameter was increased in 51 patients (47.7%). There was no association between rectal diameter ≥ 3 cm and urinary urgency, enuresis, increased daytime urinary frequency, nocturia, daytime incontinence, constipation, severe LUTS or bladder and bowel dysfunction (P > 0.05 in all cases). However, increased rectal diameter was associated with at least one episode of faecal incontinence per week in constipated patients (P = 0.02). There was no correlation between rectal diameter and dysfunctional voiding symptom score (r_s = 0.00), bladder capacity (r_s = 0.01), post-void residual urine (r_s = 0.05), bladder wall thickness (r_s = 0.00) or first volume voided after ultrasonography (r_s = 0.06); P > 0.05 in all cases.

Conclusion: There was no association between the current cut-off point characterising the rectum as distended and the severity of urinary symptoms, even when FC was present. However, the complaint of faecal incontinence associated with increased rectal diameter may suggest functional constipation. The cross-sectional design, however, constitutes a limitation. Further studies may be able to determine the ideal diagnostic cut-off point for bowel and urinary dysfunction. Rectal diameter was not associated with the intensity of LUTS, with or without FC. However, the complaint of faecal incontinence associated with increased rectal diameter may suggest functional constipation.