Abscess of the psoas muscle resulting usually from disease of the lumbar vertebrae, with the pus descending into the muscle sheath. The infection is most commonly tuberculous or staphylococcal. ... (12 Dec 1998) ... 
Problem most associated with tuberculosis although it occurs in appendicitis. The psoas is a muscle in the pelvis
Type: Term Definitions: 1. an abscess, usually tuberculous, originating in tuberculous spondylitis and extending through the iliopsoas muscle to the inguinal region.