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  1. Rebecca Greenhalgh, radiology specialist registrar1,
  2. C Richard Cohen, consultant colorectal surgeon1,
  3. David Burling, consultant radiologist2,
  4. Stuart Andrew Taylor, senior lecturer in radiology and honorary consultant radiologist13
  1. 1University College Hospital, London NW1 2BU
  2. 2St Mark’s Hospital, Harrow HA1 3UJ
  3. 3University College London, London
  1. Correspondence to: S A Taylor stuart.taylor{at}uclh.nhs.uk
  • Accepted 15 October 2007

This article explores the radiological investigations available to diagnose perianal pain of unknown cause, with particular reference to perianal sepsis

Learning points

  • Imaging plays an important role in elucidating the cause of anal pain when the diagnosis is not clinically apparent

  • Endoanal ultrasound is an increasingly available, relatively inexpensive, quick and safe technique providing high resolution images of the anal sphincter complex, and intersphincteric space, but it is limited by a relatively small field of view

  • Magnetic resonance imaging, although not universally available, affords much greater anatomical coverage than endoanal ultrasound and can also image the perirectal tissues and lumbar-sacral spine, facilitating diagnosis of conditions beyond the anal canal

  • In the case of perianal sepsis, preoperative magnetic resonance imaging may be indicated in clinically suspected complex or recurrent disease to guide surgery, reducing the risk of future recurrence

The patient

A 29 year old woman presented with constipation, constant perianal burning, and pain on defecation. Digital rectal examination was uncomfortable with induration in the right posterior quadrant, but there was no evidence of anal fissure or skin tag, thrombosed haemorrhoid, perianal haematoma, anal mass, or palpable abscess or fistula. Perianal skin sensation was normal.

What is the next investigation?

The aim of further investigation is to identify those causes of perianal pain not always detected by direct clinical examination. Commoner causes to consider include occult perianal sepsis such as intersphincteric abscess (the prevalence of anal fistula in the general population is about 0.01%1), anal complications of inflammatory bowel disease, and anal cancer. Rarer causes include retrorectal developmental cysts, sacrospinal tumours, and sacral nerve tumours. Proctalgia fugax (intermittent severe anal …

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