Imaging of perianal fistulizing Crohn’s disease

Abstract

Perianal fistula is a complication of Crohn’s disease that carries a high morbidity. It is a channel that develops between the lower rectum, anal canal and perianal or perineal skin. The development of perianal fistulas typically connotes a more aggressive disease phenotype and may warrant escalation of treatment to prevent poor outcomes over time. Based on fistula anatomy, debris can form inside these tracts and cause occlusion, which subsequently leads to abscess formation, fever and malaise. The clinical presentation is often with complaints of pain, continuous rectal drainage of fecal matter as well as malodorous discharge. Considering that the presence of fistulas often indicates refractory and aggressive disease, early identification of its presence is important. Some patients may not have the classic symptoms of fistulizing disease at presentation and others may have significant scarring and/or pain from previous fistulizing episodes, which can make an accurate assessment on physical exam alone problematic. As a result, utilizing diagnostic imaging is the best means of identifying the early signs of perianal fistulas or abscess formation in these patients. Several imaging modalities exist which can be used for diagnosis and management. Endoscopic ultrasound and pelvic MRI are considered the most useful in establishing the diagnosis. However, a combination of multiple imaging modalities and/or examination under anesthesia is probably the most ideal. Incomplete characterization of the fistula tract(s) extent or the presence of abscess carries a high morbidity and far-reaching personal expense for the patient – promoting worsening of the disease.

Keywords:

• endoscopic ultrasound
• fistulizing Crohn’s disease
• MRI
• perianal Crohn’s disease
• perianal fistula

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending or royalties.

Key issues

• Perianal fistula is a complication of Crohn’s disease (CD), which can be a cause of major morbidity in patients regardless of whether it is present early or late in their CD course. MRI, endoscopic ultrasound (EUS) or a combination for accurate and timely identification would mean earlier intervention and appropriate management when escalation of care or a multidisciplinary approach is necessary.

• The diagnostic imaging results can be pivotal in medical and surgical management decision-making. A readily available, highly accurate modality which would not necessitate operator endoscopic training is MRI. However, in cases where there is available expertise, EUS is an option to be considered.

• Although several imaging modalities exist, some are not as sensitive and can miss fistulas that do not have external opening. Others may be prone to missing abscesses.

• Clinical assessment should precede the choice of imaging. Patients with anal strictures may not always be the ideal candidates for certain modalities, which would involve insertion of a probe into the rectum. In addition, scheduling of some imaging modalities can coincide with planned procedures like colonoscopies since the patients will already be under sedation.

• MRI, EUS in intervals of no greater than 6 months is recommended in patients with active perianal fistulizing Crohn’s disease.

• Studies over the years have suggested that combining specific imaging modalities alone or with examination under anesthesia increases the sensitivity for the diagnosis of fistulas. Some limitations for the more preferred imaging modalities include cost and dependence on operator expertise.

• The consensus statement from European Crohn’s and Colitis Organization-European Society of Gastrointestinal and Abdominal Radiology identify MRI as a single most appropriate modality considering accuracy, availability and less reliance on expertise of endoscopist, especially in complex and recurrent fistulas. American Gastroenterological Association favors either EUS or MRI either alone or in combination with exam under anesthesia, but the latter should not be done alone as the means of identifying perianal fistulas.