Low anterior resection syndrome

Did You Know?

• Low anterior resection syndrome falls into two groups: one with fecal urgency, incontinence, and increased frequency; the other with constipation, a sense of incomplete evacuation, and trouble emptying the bowels.
• Some patients describe characteristics from both groups, either switching back and forth or going through both at once.

Causes

Low anterior resection syndrome emerges after rectal resection. Low tumor height and radiation, either pre- or post-operative, negatively affect bowel function. Temporary stomas and those in place for an extended length are also linked to worse bowel function, likely reflecting tumor height and surgical complications.

Mechanism

Multiple factors likely contribute. During intersphincteric resection, the internal anal sphincter may sustain direct structural damage or secondary damage from an anastomotic device inserted through the anus. Damage to the nerve supply of the internal anal sphincter can occur if the surgical approach reaches the posterolateral side of the prostate in men. The conjoint longitudinal muscle may be damaged during dissection of the intersphincteric space, and the rectococcygeus muscle is frequently divided to achieve a sufficient horizontal margin, impairing its function. Poor compliance from rectal volume loss decreases maximum allowable rectal volume and increases false urge to urinate. Injury to extrinsic spinal cord nerves mediating the rectoanal inhibitory reflex may also cause intestinal dysfunction.

Diagnosis

Low anterior resection syndrome can be assessed using two validated patient questionnaires. The 18-item Memorial Sloan Kettering Cancer Center Bowel Function Instrument (MSKCC-BFI) was developed in 2004. The 5-item LARS score was developed in 2012 by Emmertsen et al. in a Danish population. Anorectal manometry objectively assesses anal sphincter function and rectal capacity by recording resting pressure, maximum squeezing pressure, rectoanal inhibitory reflex, rectal capacity, and compliance, though it is not necessary for diagnosis. Endoscopic rectal ultrasound evaluates the pelvic floor and sphincter complex structure. Fecoflowmetry tracks changes in flow against time to evaluate anorectal motor function.

Treatment

The foundation of treatment is conservative therapy, including pelvic floor rehabilitation, colonic irrigation, or minimally invasive procedures such as spinal nerve stimulation. For short-term treatment of a single symptom, loperamide or antibiotics like neomicine or rifaximin may be used. Bile acid sequestrants like colesevelam and 5-HT3 antagonists like ramosetron have shown early results but need more research. Transanal irrigation is an inexpensive and successful treatment for high defecation frequency and incontinence. Sacral nerve stimulation improves fecal incontinence and deferred defecation. When fecal incontinence becomes unmanageable, surgery may be considered; a stoma is an option after other treatments are exhausted, and advanced surgical techniques are reserved for a very select group of patients.