Differential Diagnoses for Abscesses

Anorectal Abscess Differential Diagnoses

The American College of Surgeons recommends considering anal cancer and precancerous conditions in the differential diagnosis for anorectal abscesses, as they can present with similar symptoms of pain, swelling, and mass effect in the perianal region 1, 2
Approximately one-third of patients with Crohn's disease will develop an anorectal abscess, and it is mandatory to exclude undiagnosed Crohn's disease in every patient presenting with anorectal abscess, especially if recurrent 1, 2, 3
Tuberculosis can present as chronic perianal infection mimicking abscess 1
Fournier's gangrene/necrotizing fasciitis is a critical distinction requiring urgent recognition, as it demands immediate aggressive surgical debridement rather than simple incision and drainage 1, 2

Brain MRI with DWI/ADC sequences and gadolinium contrast demonstrates 92% sensitivity and 91% specificity for differentiating brain abscess from tumor 4
Central hyperintensity on DWI with corresponding low ADC values strongly suggests abscess over malignancy 4
MRI may be less sensitive after several weeks of antibiotic treatment, in toxoplasmosis, and in post-neurosurgical settings 4

Pyogenic abscesses are more likely to be multiple and occur in older age groups 5
Amoebic liver abscess should be suspected in patients with appropriate travel history, and 20% will have a history of dysentery, though only 10% have diarrhea at presentation 5
Amoebic serology (indirect hemagglutination) has >90% sensitivity for amoebic liver abscess 5

For anorectal presentations, perform focused history examining for inflammatory bowel disease symptoms, recurrent infections, immunosuppression, and diabetes 1, 2
For suspected brain abscess, brain MRI with DWI/ADC sequences and T1-weighted imaging with and without gadolinium is strongly recommended as the preferred diagnostic modality 4, 8
For intra-abdominal/liver abscess, ultrasound should be performed in all patients, and CT scan if ultrasound is negative and clinical suspicion remains high 5
Obtain amoebic serology in patients with neutrophil leukocytosis, raised inflammatory markers, deranged liver function tests, and appropriate epidemiology 5
Consider hydatid serology before aspiration in patients from endemic regions 5