When Do You Drain Epidural Abscesses of the Spine?

How the relative volume of an epidural abscess on MRI affects outcomes with antibiotics alone has limited literature. The purpose of this study was to identify which infected epidural collections will reabsorb with antibiotics alone. Specifically, what is the critical size and enhancement on contrast MRIs to require a drainage procedure?

A retrospective review of all spinal osteomyelitis patients from 2001-2012 was performed. Inclusion criteria included appropriate initial imaging, lab results, no drainage procedures of collections, and no treatment prior to admission at an outside institution. Large size epidural abscess was defined as abscesses with a volume greater than 1400 mm3. Clearance and mortality rates were evaluated.

The cohort consisted of 128 patients including 76 men and 52 women who had a mean age of 62 years (range, 21 to 90 years) and had a mean follow-up of 38 months (range, 24 to 72 months). Patients with a large epidural abscess had a greater clearance rate of the infection and decreased mortality rate when treated with surgery or drainage compared to patients treated with antibiotics alone [clearance: p=0.048; mortality: p=0.048]. Those small epidural abscesses had similar clearance and mortality rates when treated with surgery or drainage compared to antibiotics alone [clearance: p=0.75; mortality: p=0.13]. Patients with non-enhancing epidural abscesses had similar clearance rates-but increased mortality rates-when treated with antibiotics alone compared to surgery or drainage [clearance: p>0.9; mortality: p=0.03]. Those with enhancing epidural collections had similar clearance and mortality rates when treated with antibiotics alone compared to surgery or drainage [clearance: p=0.08, mortality: p=0.10].

Large epidural infected collections require surgery or a percutaneous drainage procedure. Clearance rates are higher and mortality rates are lower compared to non-operative management in these instances. Neurologically intact patients with a small epidural collection can be treated with antibiotics alone with good expected outcomes.