What type of abscess is characterized by a deep location relative to the levator ani, presence of pus from the anal canal without an external opening, and a collection deep to the levator ani as seen on MRI?

Pelvirectal (Supralevator) Abscess

Based on the MRI showing a collection deep to the levator ani muscle, this is a pelvirectal (supralevator) abscess. The key anatomical landmark is the levator ani muscle, and any abscess located superior to this muscle in the supralevator space is classified as pelvirectal/supralevator 1.

Anatomical Classification and Diagnostic Reasoning

The anatomical location relative to the levator ani muscle is the critical determinant for abscess classification 1:

• Supralevator (Pelvirectal) abscesses are located superior to the intersphincteric plane in the supralevator space, which is precisely what the MRI demonstrates in this case 1
• Intersphincteric abscesses lie between the internal and external sphincter muscles 1
• Ischiorectal (Ischioanal) abscesses penetrate through the external anal sphincter into the ischioanal space, lateral to the sphincter complex 1
• Submucosal abscesses would be superficial, not deep 1

Clinical Features Supporting This Diagnosis

The clinical presentation aligns with a supralevator abscess 1, 2:

• Palpable mass above the dentate line on rectal examination is characteristic of high intermuscular or supralevator abscesses 1, 2
• No external opening is typical, as these deep abscesses do not readily point to the skin surface 2
• Pus from anal canal indicates internal drainage through the primary opening at the dentate line 2
• Negative sigmoidoscopy helps exclude rectal pathology but doesn't rule out deep perianal sepsis 1

Diagnostic Pitfalls

Supralevator abscesses are frequently misdiagnosed because they lack the typical external signs of perianal sepsis 1, 2:

• These represent only 7% of anorectal abscesses but are often missed clinically 2
• 56% of patients with high intermuscular abscesses have undergone previous inappropriate anorectal surgery due to initial misdiagnosis 2
• Digital rectal examination revealing a tender, indurated area above the anorectal ring is the key clinical finding 1
• MRI is essential for accurate diagnosis when clinical examination suggests a deep abscess, as physical examination alone may not provide the complete picture 1, 3

Management Implications

The anatomical location determines the drainage approach 4:

• Internal (transrectal) drainage is required for abscesses above the levator ani muscle 4
• External drainage would be inappropriate and potentially dangerous for supralevator collections 4
• The primary opening at the dentate line must be identified and addressed to prevent recurrence 2

Answer: D. Pelvirectal