Iliopsoas abscesses can be primary or secondary, Primary abscess being more common in neonates and infants [2, 3]. It can also occur secondary to extension of infection from an adjacent organ. The affected neonates are often sick at admission. In most cases the pathology remains unilateral, but bilateral involvement has also been reported . Limb swelling, pain, limitation of movement along with discoloration of the affected limb are the common presenting features. Abdominal mass as a presenting features has also been reported [3, 5, 6]. The clinical pictures often mimic the presentation of septic arthritis, which often remains as an important differential diagnosis [5, 6]. Sometimes, iliopsoas abscess can occur secondary to spread from underlying septic arthritis of hip .
Staphylococcus aureus is the most common infectious agent reported accounting for more than 80% of the reported cases in neonates [1, 2, 3, 9]. Klebsiella and streptococcus pneumoniae are the other pathogens being isolated from cases of iliopsoas abscess in neonates [7, 10]. In the present case, the causative organism was methicillin resistant staphylococcus aureus. Iliopsoas abscess caused by methicillin resistant staphylococcus (MRSA) is extremely rare and potentially life threatening. Only few cases of iliopsoas abscess caused by MRSA in neonates have been reported in available literature [11, 12]. Leucocytosis along with neutrophilia is a consistent laboratory abnormality reported from previous reports [1, 2, 9]. Ultrasonography is a simple bedside investigation for localisation of abscess and remains the investigation of choice. CT scan or MRI helps in better delineation of anatomy and extent of the lesion and helps in planning drainage .
Though Ultrasound guided percutaneous drainage followed by a course of appropriate antibiotic is effective , lack of availability of appropriate size of catheter, expertise in percutaneous procedure in neonate, and other technical difficulty often precludes percutaneous drainage in neonates, as in the present case.
It is often difficult to identify the source of infection in majority of cases. Few cases of iliopsoas abscess have been described to be secondary to superficial infections [2, 8]. Infection related to Central venous catheters, secondary infection of iliopsoas hematoma has been reported [1, 7, 15]. Hematogenous spread from a distant focus or septicemia also remains a possibility. Underlying immunodeficiency increases the probability of such infections, as cases secondary to leucocyte adhesion deficiency are being reported . In the present case, a definite source of infection could not be identified. The presence of retroperitoneal abscess on the same limb with peripheral intravenous canula could raise the possibility of peripheral intravenous canula being the probable portal of entry of organism but exact causal relationship is difficult to establish in the present case.