Psoas muscle abscess and fluid collections are located in the retrofascial space rather than in the retroperitoneal space because the psoas muscles are located in the iliopsoas compartment posterior to the transversalis fascia, which is the posterior boundary of the retroperitoneum.
Psoas muscle abscess may present with fever, flank pain, abdominal pain or limp. Other symptoms are nausea, malaise and weight loss.
Psoas muscle abscess may be classified as primary or secondary depending on the presence or absence of underlying disease.
Primary psoas muscle abscess occurs probably as a result of haematogenous spread of an infectious process from an occult source in the body. Primary psoas muscle abscess can occur in patients with:
Spread of infection from gastrointestinal disease (e.g. appendicitis, diverticulitis, Crohn disease or perforated colon carcinoma) is the most common source of a
secondary psoas muscle fluid collection.
Renal disease is the second most common source.
They may also occur as a result of a neighbouring spondylodiscitis.
Cross-sectional imaging is the modality of choice for abscess detection in the psoas muscle. Extension from the psoas muscle into the iliacus muscle is a common sequela.
It is diagnostic in only 60% of cases of psoas abscess, compared with 80% to 100% for CT.
Treatment and prognosis
Appropriate antibiotics along with drainage of the abscess is the treatment of choice. This is often treated with a image-guided percutaneous drainage, typically CT, due to the retroperitoneal location.
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