Differential Diagnosis for Chronic Anal Discharge with No External Opening
- Single most likely diagnosis:
- Intersphincteric fistula: This is the most likely diagnosis given the presence of a track from 2 o'clock to 6 o'clock about 5 cm away from the anal orifice on MRI. Intersphincteric fistulas are the most common type of anal fistula and typically run between the internal and external anal sphincters, which could explain the lack of an external opening and the described track.
- Other Likely diagnoses:
- Ischiorectal fistula: Although less common, an ischiorectal fistula could also present with chronic anal discharge and might not have an obvious external opening. The track's location could potentially be consistent with an ischiorectal fistula, especially if it extends into the ischiorectal fossa.
- Levator ani abscess: An abscess in the levator ani muscle could cause chronic discharge if it communicates with the anal canal, and its location could be consistent with the described MRI findings. However, the presence of a distinct track is more suggestive of a fistula.
- Do Not Miss diagnoses:
- Perianal or rectal cancer with fistula formation: Although rare, cancer can cause fistula formation and should be considered, especially in older patients or those with risk factors for colorectal cancer. Missing this diagnosis could have severe consequences.
- Inflammatory bowel disease (IBD) with fistula: Conditions like Crohn's disease can cause complex fistulas, including those without obvious external openings. IBD should be considered, especially if there are other symptoms suggestive of inflammatory bowel disease.
- Rare diagnoses:
- Supralevator abscess: This is an abscess located above the levator ani muscles and could potentially cause chronic discharge if it communicates with the anal canal. However, it is less likely given the described location of the track.
- Hidradenitis suppurativa with perianal involvement: This chronic skin condition can cause fistulas and abscesses, including in the perianal region. While it's a less common cause of the described symptoms, it should be considered in patients with a history of hidradenitis suppurativa.