Psoas Abscess: Imaging Diagnosis of A Rare Entity

Abstract

Psoas abscess (PA) is a rare infection which may present as pus collection in the ilio-psoas muscle compartment. Mynter et al described this entity for the first time in 1881. Its incidence is so rare that less than 15 patients are diagnosed every year in whole world. It is not only a rare infection but also it is an under diagnosed entity because of its non-specific and vague symptomatology. These abscesses are many times under-diagnosed despite availability of improved diagnostic modalities. The diagnosis require a high index of suspicion specially in patients of diabetes, patients on immunosuppressants, individuals receiving chemotherapy and patients with acquired immunodeficiency syndrome. The Psoas abscesses are divided into primary and secondary PA on the basis of the etiology. The exact etiology of primary Psoas abscess is not known but it is thought to be secondary to hematogenous spread. The secondary Psoas abscess is thought to be secondary to spread of infection from the adjacent sites like from pott's spine or secondary to urinary tract infection, post spine-surgery, in patients with mycotic aneurysms, individuals with endocarditis and pyogenic osteomyelitis etc. The common organisms involved in PA include S.Aureaus, E.Coli, Bacteroids, M.Tuberculosis, Enterococcus and peptostreptococcus. Patients may present with the classical triad of Pain, Fever and Limp. A timely diagnosis and immediate and aggressive treatment is essential as these abscesses carry a very high mortality if not treated in time. The imaging techniques which may be used for the diagnosis include Ultrasound Imaging, Computerised Tomography and Magnetic Resonance Imaging. Plain Radiographs are usually unremarkable. The fact that Psoas muscle abscess are located in the retrofascial space rather than in the retroperitoneal space makes its diagnosis difficult on ultrasound examination and approximately 40% of the times the diagnosis of Psoas abscess is missed on ultrasonography. Diagnosis by CT and MRI is relatively easy and almost all cases can be diagnosed on the basis of CT or MRI. Unenhanced CT may show presence of abscess within the Psoas muscle. A CT-Scan with oral and IV contrast may be needed in some cases of Psoas abscess where the abscess is suspected to be secondary. CT may also help in CT Guided drainage of abscess which may have diagnostic (culture and sensitivity) and therapeutic implications. MRI may provide better visualization of abscess than CT scan moreover MRI can simultaneously rule out other causes of low back pain. In some advanced centers gallium-67 scanning is being used for the diagnosis of Psoas abscess but its routine use is not feasible in developing countries like that of India. We are reporting here a case of Psoas abscess in 25 year old female who were sent for referred to us for CT abdomen. She had a history of fever, right flank pain, nausea and referred pain to groin. We diagnosed her to be having Psoas Abscess on the basis of imaging findings. Patient received appropriate treatment in the form of draina...