Iliopsoas abscess is a relatively uncommon condition that can present with vague clinical features. Its insidious onset and occult characteristics can cause diagnostic delays, resulting in high mortality and morbidity. The epidemiology, aetiology, clinical features, and management of iliopsoas abscess are discussed.
- IVU, intravenous urogram
- PCD, percutaneous drainage
- iliopsoas abscess
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Before the discovery of modern antituberculosis treatment iliopsoas abscess was characteristically a well recognised complication of tuberculosis of the spine. However with the decreasing prevalence of tuberculosis, iliopsoas abscess is becoming uncommon in the developed countries. Iliopsoas abscess is a collection of pus in the iliopsoas compartment. Iliopsoas abscess was first described by Mynter in 1881 who referred to this as psoitis.1
ILLUSTRATIVE CASE HISTORY
A previously well 40 year old man presented with a two day history of right loin to groin pain and nausea. He denied any dysuria, fever, or chills. Physical examination was unremarkable except for moderate tenderness in the right loin on pressure. Urine dipstix was 1+ positive for blood, however urine microscopy was normal. His white cell count was raised at 14.0 × 109/l.
A plain radiograph of the kidney ureter bladder did not show any evidence of a calculus. An ultrasound scan of the abdomen revealed a right hydronephrotic kidney with a right hydroureter. No definite renal calculus was seen. An intravenous urogram (IVU) was performed which confirmed the ultrasound findings (fig 1). The pain settled down and it was assumed that the stone had been passed. He was discharged home on analgesics with a follow up appointment. One week later he was seen again urgently with similar pain. Cystoscopy with right retrograde pyelogram was performed which did not show any obstruction of the renal tracts. Meanwhile his blood haemoglobin dropped to 77 g/l. Three units of red cells were transfused to correct the anaemia. Computed tomography of the abdomen and pelvis was performed which revealed a right iliopsoas abscess (fig 2). Broad spectrum intravenous antibiotics were started and an emergency laparotomy was performed. At operation the distal third of the ileum was found stuck to the right iliopsoas muscle as a mass with abscess formation. The right ureter was found to be adherent to the posterior abdominal wall with hydroureter proximally. Ileocaecal resection and drainage of the abscess was performed. A right ureteric stent was also inserted at the same time. Antibiotics were continued for a week. The pus grew Escherichia coli and the histology of the specimen was confirmed as Crohn’s disease. A month later he presented with a recurrent iliopsoas abscess, which was drained surgically. The ureteric stent was removed two months after its insertion. A repeat IVU was normal with no hold-up of contrast. Two years on, he is doing well without any further complications.
The iliopsoas compartment is an extraperitoneal space which contains the iliopsoas and iliacus muscles. The psoas major is a long fusiform muscle placed on the side of the lumbar region of the vertebral column and brim of the lesser pelvis (fig 3). It arises from the lateral borders of T12 to the L5 vertebrae. The muscle proceeds downward across the brim of the lesser pelvis and diminishing gradually in size, passes beneath the inguinal ligament and in front of the capsule of the hip joint and ends in a tendon. The tendon receives nearly the whole of the fibres of the iliacus muscle and is inserted into the lesser trochanter of the femur. The psoas major and iliacus are sometimes regarded as a single muscle named the iliopsoas. It is innervated by the branches of L2, 3, and 4, and it is the primary flexor of the hip joint. The psoas muscle lies in close proximity to organs such as the sigmoid colon, appendix, jejunum, ureters, abdominal aorta, kidneys, pancreas, spine, and iliac lymph nodes. Hence infections in these organs can spread to the iliopsoas muscle. The abundant blood supply of the muscle is believed to predispose it to haematogenous spread from occult sites of infection.2
Iliopsoas abscess may be classified as primary or secondary, depending on the presence or absence of underlying disease. Primary iliopsoas abscess occurs probably as a result of haematogenous spread of an infectious process from an occult source in the body. The group of patients in which primary iliopsoas abscess occurs is summarised in box 1.3 Crohn’s disease is the commonest cause of secondary iliopsoas abscess.4 The other causes of secondary iliopsoas abscesses is summarised in table 1. Patients who have had instrumentations or procedures performed in the groin, lumbar, or hip areas are at a particular risk of developing an iliopsoas abscess.5–7 In a review of 367 cases, Ricci et al noted world wide differences in its aetiology.8 In Asia and Africa, over 99% of iliopsoas abscess are primary, whereas 17% and 61% are primary in Europe and North America respectively.8 Iliopsoas abscess is common in the young compared with the elderly.9 It is reported to be commoner in males than females.10,11 Bresee et al in a study of 142 paediatric patients with iliopsoas abscess found a 57% occurrence on the right side, 40% on the left side, and 3% had bilateral abscesses.12 The mortality rate in primary iliopsoas abscess is 2.4% and in secondary abscesses is 19%.13 Ricci et al suggested that the mortality rate in untreated patients is 100%.8
Box 1: Primary iliopsoas abscess can occur in:
Intravenous drug abuse.
Staphylococcus aureus is the causative organism in over 88% of patients with primary iliopsoas abscess.8 Secondary iliopsoas abscess is caused by streptococcus species 4.9% and E coli 2.8%.8Mycobacterium tuberculosis as a cause of iliopsoas abscess is currently uncommon in the western world, but common in the developing countries. The other causative organisms include proteus,9Pasteurella multocida,14 bacteroides,15 clostridium,16Yersinia enterocolitica,17 klebsiella,18 methicillin resistant Staphylococcus aureus,19 salmonella,20Mycobacteriumkansasii,21 and Mycobacterium xenopi.22
The clinical presentation of iliopsoas abscess is often variable and non-specific. The classical clinical triad consisting of fever, back pain, and limp is present in only 30% of the patients with iliopsoas abscess.23 As the psoas muscle is innervated by L2, L3, and L4, pain can radiate to hip and thigh. Other symptoms are vague abdominal pain, malaise, nausea, and weight loss. The clinical features are summarised in box 2.
Box 2: Clinical features
Lump in the groin.
A diligent physical examination is essential for the prompt diagnosis of this condition. The diagnosis may be obvious if the patient is noted to favour the position of greatest comfort. This is the supine position with the knee moderately flexed and the hip mildly externally rotated.24 There are well defined signs to elicit in patients with iliopsoas abscess, though they are not very specific of this condition. The principle of these tests is that the psoas muscle is the main flexor of the hip (box 3). Patients may present with a painless swelling below the inguinal ligament (fig 4). This may be confused with a femoral hernia or enlarged inguinal lymph nodes. In this instance, it presents as a reducible swelling with an impulse on coughing. An iliopsoas abscess secondary to Crohn’s disease may compress the ureter and present with hydronephrosis (as illustrated in the case history). A large iliopsoas abscess may present with deep venous thrombosis.25 The cause of the thrombosis is due to extrinsic compression of the iliac vein from the iliopsoas abscess.26
Tumours arising from the structures within the pelvis or lumbar area may mimic an iliopsoas abscess.27–31 A physician attending such a patient must be aware as the treatment is different in these cases.
Box 3: Tests to elicit iliopsoas inflammation
The examiner places his hand just proximal to the patient’s ipsilateral knee and the patient is asked to lift his thigh against the examiner’s hand. This will cause contraction of the psoas and results in pain.
With the patient lying on the normal side, hyperextension of the affected hip results in pain as the psoas muscle is stretched.
NB: These tests may be positive in appendicitis in which there is inflammation of the iliopsoas without the formation of iliopsoas abscess.
Laboratory investigations may reveal a raised white cell count, raised C-reactive protein, anaemia, and raised erythrocyte sedimentation rate.2 Blood cultures may be positive for a particular organism causing the abscess. Initial radiological investigations may include radiography of the kidney ureter bladder, an IVU, or barium enema. These are neither specific or sensitive and are unhelpful in the diagnosis of iliopsoas abscess. Sometimes gas forming abscesses can be seen as mottled gas shadows in the retroperitoneum.32,33 Ultrasound is inexpensive, has no radiation effects, and is easy to perform but is extremely operator dependent. Ultrasound is diagnostic in only 60% of the cases.8,33 The retroperitoneal space can be difficult to visualise ultrasonically and can be obscured by bowel gas.34 Computed tomography should be done for definitive diagnosis and is considered the “gold standard”.11 Some authors believe that magnetic resonance imaging is superior to computed tomography because of better discrimination of soft tissues and the ability to visualise the abscess wall and the surrounding structures without the need of a intravenous contrast medium.13,35
Treatment involves the use of appropriate antibiotics along with drainage of the abscess. An adequate knowledge of the causative organisms should guide the initial choice of antibiotics. Depending on the results of the abscess fluid culture and sensitivity, adjustments should be made. In patients suspected to have primary iliopsoas abscess, antistaphylococcal antibiotics should be started before the culture results.9 In secondary iliopsoas abscess it is wise to start patients on broad spectrum antibiotics like clindamycin, antistaphylococcal penicillin, and an aminoglycoside.12 Drainage of the abscess may be done through computed tomography guided percutaneous drainage (PCD) or surgical drainage. PCD is much less invasive and has been proposed as the draining method of choice.36–38 Mueller et al reported first application of PCD in iliopsoas abscesses in 1984.39 In a study of 22 patients of whom 20 patients had primary and two had secondary iliopsoas abscesses, Cantasdemir et al found that PCD was effective in 21 out of the 22 patients.40 This procedure is associated with a low morbidity and mortality. The indications of operation are (a) failure of PCD, (b) relative contraindication of PCD, for example, clotting disorders, and (c) the presence of an another intra-abdominal pathology which requires surgery. In patients with Crohn’s disease, performing a single operation to drain the abscess and resect the diseased bowel is desirable.41 Sometimes PCD can be a useful initial treatment to improve the patient’s condition before surgery.42 Antibiotics are sometimes continued up to two weeks after complete abscess drainage.
It is prudent that this condition is recognised and managed promptly. Early management and drainage of the abscess reduces the morbidity and mortality.