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 and might not have a visible external opening. However, the presence of a defined track on MRI makes this less likely compared to a fistula.
- Do Not Miss diagnoses:
- Perineal abscess: Although a perineal abscess might seem less likely given the lack of an external opening and the specific location of the track, it's crucial not to miss this diagnosis due to its potential for severe complications if left untreated. However, the described track and lack of external signs make this less probable.
- Rare diagnoses:
- Hidradenitis suppurativa with perianal involvement: This condition can cause chronic discharge and fistulas but typically involves the skin and has visible external signs, making it less likely in this scenario.
- Crohn's disease with perianal fistula: While Crohn's disease can cause perianal fistulas, the presentation usually includes other symptoms such as diarrhea, weight loss, and abdominal pain, which are not mentioned in the scenario.