Fecal impaction

Faecal impaction is the inability to spontaneously evacuate solid faeces. It is common in the elderly population. A severe form of faecal impaction is often referred to as a faecaloma. 

Terminology

Faecal loading is a poorly defined term but generally refers to the volume of faecal material in the colon, it is often used synonymously with faecal impaction. A causative relationship between faecal loading and symptoms (e.g. constipation, bloating, diarrhoea) has not been established ^4,5. 

Epidemiology

Faecal impaction is common and usually seen among the elderly, bedridden patients or incapacitated people ^1,2.

Risk factors

• chronic or severe constipation

• sedentary lifestyle

• low fibre diet

• certain medication, e.g. opioids ^1,2

• history of faecal impaction ³

Clinical presentation

Patients may complain of constipation, rectal discomfort, abdominal pain, tenderness or distension ^1-3.

Pathology

Faecal impaction is most commonly a complication of chronic or severe constipation where inspissated hard faeces accumulates in the distal gastrointestinal tract, most commonly the rectum ³. Other causes include anatomical causes (e.g. megarectum, anorectal stenosis, malignancy) or functional causes (e.g. pelvic floor dysfunction) ³. 

Radiographic features

Plain radiograph

Faecal impaction may be seen as a speckled low-density soft tissue mass within a distended large bowel, most commonly the rectum ^1,2. 

Ultrasound

Transabdominal point-of-care ultrasonography (POCUS) has been described as an adjunct in the diagnosis of faecal impaction and chronic constipation. Serial examinations may also provide evidence of treatment efficacy (e.g. repeat imaging after enema insertion).

Pertinent views to obtain include a transverse (axial) imaging plane just cephalad to the pubic symphysis with caudad tilting and an orthogonal sagittal (longitudinal) view.

A posterior approach is an alternative, placing the patient in a lateral decubitus position with maximal hip and trunk flexion with the transducer between the coccyx and anus ⁸. The exam is feasible with or without an optimally distended urinary bladder, the latter is, however, preferable.

Sonographic features described include ⁷:

• an increase in the transverse diameter of the rectum (TRD)

  • values exceeding 27-38 mm suggest constipation and/or faecal impaction ⁶

    • patients with constipation may have mean rectal diameters reaching 34-41 mm

    • normal controls mean TRD of 20-24 mm

  • increased rectal wall thickness may also be present

• hyperechoic convex crescent just deep to anterior wall of the rectum consistent with the presence of stool ("faecal loading")

  • posterior acoustic shadowing appears with increasingly dense faeces

  • longitudinal views may define the precise location of impacted stool

  • rectum without faecal loading hypoechoic, resembles collapsed ovoid

Complications

Untreated faecal loading may lead to an increase in large bowel pressure with possible bowel obstruction, stercoral colitis and/or stercoral perforation ^1,2.

Treatment and prognosis

Impacted faecal removal may be performed manually, with water irrigation, enema, laxatives or with rectal cleansing under sigmoidoscopy ^1,2.

Physical activity, fibre-rich diet, sufficient fluid intake and prokinetic drugs are prescribed to stimulate transit and to change the stool consistency, thus preventing recurrence ^1,2.