1 Introduction

Iliopsoas abscess (IPA) is a relatively uncommon condition that can present with vague clinical features due to containment of pus in the iliopsoas compartment of muscles.¹ Primary IPA occurs due to the spread of a causative organism from a distant site to the iliopsoas via hematogenous or lymphatic route. Secondary IPA occurs because of the direct extension of a nearby infective process into the iliopsoas.²

Many patients will present with an insidious onset of non-specific features such as malaise and low-grade pyrexia, abdominal discomfort, pain on movement of the hip, specifically in flexion and external rotation.^3,4 Approximately 30% of patients with a psoas abscess present with the classical triad of fever, back pain, and psoas spasm.⁵ As L2, L3, and L4 nerve roots innervate the psoas muscle, patients can rarely present with back pain radiating to the hip and thigh.^2,6 Due to its insidious onset and occult clinical characteristics iliopsoas abscess can cause diagnostic delays, which may result in high mortality and morbidity.^7,8

Iliopsoas abscess may extend to the epidural space causing the surgical emergency of cauda equina syndrome, which is an extremely rare presentation, though several cases have been reported.⁹ Acute cauda equina syndrome presents with pain on the buttock and lower extremity, saddle anesthesia, motor and sensory dysfunction of lower limbs, as well as bowel/bladder dysfunction.^10,11

Diagnostic methods of iliopsoas abscess include laboratory investigations including complete blood count (CBC), C-reactive protein (CPR), and erythrocyte sedimentation rate (ESR) to confirm the diagnosis of an inflammatory focus.² Imaging is required to confirm the diagnosis and further treatment plan. Plain radiographs are unremarkable unless there is underlying vertebral osteomyelitis. Ultrasonography (USG) can diagnose iliopsoas abscesses with only 60% sensitivity; MRI can diagnose with 90% sensitivity and 80% specificity.^12,13 However, MRI can provide additional information on potential back pain and radiculopathy sources. Ultimately, definitive diagnosis can be achieved with CT-guided drainage and culture of fluid in absence of any surgical emergency.¹⁴

This report aimed to report a case of iliopsoas abscess presenting with acute low back pain and radiculopathy, which later progressed to cauda equina syndrome, and was managed with posterior decompression.

2 Case report

A 31-year-old man presented to our outpatient department with the chief complaints of low back pain radiating to bilateral lower limb for last three weeks and weakness of bilateral lower limbs for previous five days. There was no history of associated history of fever and chills, and respiratory, abdominal, or neurologic symptoms. The patient had no history of significant trauma or a contributing medical history. He denied using alcohol and tobacco and had normal sleep and appetite, and normal bowel and bladder habits.

On physical examination, his vital signs were normal. There was no tenderness on palpation over the lumbar spine or bilateral paraspinal muscles. On right lateral position, a boggy swelling with deep tenderness was appreciated in the lumbar paraspinal area and over the sacroiliac joint on the right side. The tone was decreased in bilateral lower limbs. Sensation in both lower extremities was normal. Power was 4/5 on the L4-S1 myotome on the right side and L5-S1 myotome on the left side as per modified Medical Research Council (MMRC) grading. ASIA motor score was 95/100 as shown in Fig. 1.¹⁵ Knee and ankle reflexes were absent and plantar reflexes were mute bilaterally. The straight-leg-raising test (SLRT) was positive at 30° on the right side and at 50° on the left side. Cross SLRT, Bragards test, and Lasegue test were positive bilaterally. Bulbocavernous reflex, anal tone, and perianal sensation were present. The upper limb, hip, per rectal examination, and other system examinations were unremarkable.

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Fig. 1 ASIA chart of the patient at the time presentation.

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3 Diagnostic assessment

Blood investigation revealed leukocytosis with White Blood Cell count (WBC) of 18,600/μL, and increased Erythrocyte Sedimentation Rate (ESR) (88mm/hour) and C-Reactive Protein (CRP) (121mg/L) levels. Renal function test and liver function test were normal and viral markers were non-reactive. Chest X-ray did not reveal any specific findings. X-ray of dorsolumbar spine also did not reveal any significant finding except for the loss of lumbar lordosis as shown in Fig. 2. USG of the pelvis and lumbosacral region showed a heteroechoic collection of size 8.5 ∗4.4 cm2 in the right iliac muscle with bulky right iliacus and psoas muscle with hypoechoic areas within the parenchyma, and subcutaneous edema was seen in the lumbosacral region. NCCT whole spine showed paraspinal, gluteal, and iliopsoas collections on the right side, and visualized bone appeared normal except for degenerative changes, as shown in Fig. 3. MRI of the lumbosacral spine revealed epidural abscess compressing thecal sac behind the body of L5 with multiple peripherally enhancing multiloculated collections in iliopsoas region with continuation of iliopsoas abscess to epidural space through L5-S1 neural foramina and compressing the cauda equina, whereas whole spine screening scan did not show any involvement of the cervical and thoracic spine as shown in Fig. 4. Compression at the level of L5 vertebral body and neurological level at L4 was explainable due to extraspinal compression of L4 root on right side. Based on the above finding, diagnosis of lower motor neuron paraparesis secondary to epidural abscess with neurological level L4 with Frankel D neurology was made.

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Fig. 2 Pre-operative plain radiograph of dorso-lumbar spine Anterior-posterior and a lateral view showing loss of lumbar lordosis.

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Fig. 3 Pre-operative NCCT whole spine; A: Axial view at S1 sacral body area; B: Coronal view at lumbosacral area; C: Right parasagittal view; D: Midsagittal view; E: Left parasagittal view: showing paraspinal, gluteal, and iliopsoas collections on the right side, and bone showing degenerative changes.

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Fig. 4 Pre-operative MRI of the lumbosacral region with whole spine screening; A: T2 weighted images of mid-sagittal whole spine screening, showing epidural abscess compressing thecal sac behind the body of L5 and no abnormalities on cervical and thoracic spine screening; B and C: T2 weighted images mid-sagittal, coronal and axial at L5 showing multiple peripherally enhancing multiloculated collections in iliopsoas region with continuation of iliopsoas abscess to epidural space through L5-S1 neural foramina and compressing the cauda equina roots.

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4 Therapeutic intervention

He was kept on empirical intravenous antibiotics and intravenous analgesics and was advised bed rest, and dietary modification with high protein and high calories. After a period of three days of hospital admission, his neurology deteriorated suddenly, and he developed saddle-like anesthesia, bowel and bladder incontinence- features consistent with cauda equina syndrome.

After the diagnosis of cauda equina syndrome secondary to iliopsoas abscess, an emergency posterior decompression was planned. After taking the patient's consent for the planned procedure, the he was taken under general anesthesia in prone position on a spine table. The procedure was performed by a team of consultant orthopedic spine surgeons. After posterior midline incision, posterior decompression by right sided hemilaminectomy of L5 was performed, and through the Kambin triangle, the epidural space was reached and epidural abscess was drained without entering or damaging the disc. About 50 ml of pus was evacuated intraoperatively, and a pus sample was sent for gram stain, aerobic pus culture, Acid-fast bacillus (AFB) stain, and also Cartridge-based Nucleic Acid Amplification Test (CB-NAAT) to rule out tuberculous infection. Intraoperative pus sample for gram stain revealed few polymorphonuclear cells and the aerobic culture showed growth of Staphylococcus aureus. Mycobacterium complex was not detected on AFB stain and CB-NAAT. The patient was continued on intravenous vancomycin (injection Vancomycin 500mg intravenous twice daily for 21 days) postoperatively as per the culture sensitivity report.

5 Follow-up and outcomes

Postoperatively he developed occasional discharge from the operated site for which regular wound dressing and serial monitoring with blood marker of inflammation (ESR, CRPH, CBC) were done. Wound discharge subsided over 20 days, and blood markers of inflammation were persistently decreasing after surgery. He was discharged on 22nd postoperative day with a week of oral antibiotics (Linezolid 600mg per oral twice daily for one week). At final follow-up of one year, complete resolution of neurological deficit was evident with ASIA motor score of 100/100 (Fig. 5).

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Fig. 5 At one year follow up, plain radiograph of lumbo-sacral spine anterior-posterior and lateral view showing maintained lumbar lordosis with maintained disc space height, with absent lamina of L5 on right side.

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6 Discussion

The abscess formation in the group of iliopsoas muscles is uncommon. It may be either primary or secondary. The primary abscess is more common in patients with associated co-morbidities like diabetes mellitus, intravenous drug abuse, acquired immunodeficiency syndrome, renal failure, and immunosuppressive status.¹⁶ Secondary abscess may be due to hematogenous or lymphatic spread from different sites; from gastrointestinal infections like Crohn's disease, diverticulitis, appendicitis, colorectal cancer; genitourinary infections like urinary tract infection, urogenital tumors; musculoskeletal infections like vertebral osteomyelitis, septic arthritis, infective sacroiliitis; vascular-related infections like infected abdominal aortic aneurysm, femoral vessel catheterization; and miscellaneous conditions like endocarditis, intrauterine contraceptive device, suppurative lymphadenitis.¹Staphylococcus aureus is the most common causative organism, which is positive in over 88% of patients with primary iliopsoas abscess, whereas secondary iliopsoas abscess can be due to many species of organisms but is commonly caused by streptococcus species and E coli.¹⁷Mycobacterium tuberculosis although a rarity nowadays but it is still common in developing countries.^2,18 In our case the patient did not have any co-morbid conditions; also the associated symptoms were unclear, except for symptoms of iliopsoas abscess and cauda equina syndrome, so the exact cause of iliopsoas abscess remains unclear. But the organism isolated on culture of the intra-operative sample was staphylococcus aureus, which remains the most common organism in primary iliopsoas abscess.

Iliopsoas abscess presents with a wide range of symptoms including malaise, weight loss, anorexia, nausea, and radiculopathy, but the classical triad of fever, back pain, and psoas spasm is seen in only around 30% of patients.^3–5 As the psoas muscle is located along the lateral borders of the lumbar vertebrae, radiculopathy can occur easily with mechanical compression of, or direct inflammatory spread to the spinal nerve, which may be confused with the other cause of low backache of spinal origin19. In rare conditions the patient may present with features of pain on the buttock and lower extremity, saddle anesthesia, motor and sensory dysfunction of lower limbs, as well as bowel/bladder dysfunction, which may be due to extension of the abscess to the epidural space causing cauda equina syndrome.⁹ The possible tract for the extension of iliopsoas abscess to the epidural space is through the neural foramina along the nerve root.²⁰ In our patient, the he presented with low back pain radiating to the bilateral lower limb and weakness of the bilateral lower limb, which was being managed on intravenous antibiotics and analgesics, but suddenly the neurology got deteriorated and had saddles like anesthesia, bowel and bladder incontinence; which are the features consistent with cauda equina syndrome.

The iliopsoas abscess is more difficult to diagnose because of the deeper location and the ambiguity of the symptoms. So the complete history, clinical examination, laboratory investigations, and radiological co-relation are required to get to the diagnosis. Laboratory investigations may reveal raised WBC, ESR, and CRP.²¹ Initial radiological investigations may include radiography of the kidney ureter bladder and radiographs of the spine.¹ Ultrasound, although it is inexpensive, has no radiation effects, and is easy to perform but it is extremely operator-dependent, so have a diagnostic value in only 60% of the cases.^17,22 Computed tomography is considered as a gold standard and it should be done for definitive diagnosis.²³ Whereas, some authors believe that magnetic resonance imaging is superior to computed tomography because of better discrimination of soft tissues and the ability to visualize the abscess wall and the surrounding structures without the need of an intravenous contrast medium.²⁴ In our case, the diagnosis was suspected after detailed history and clinical examinations, and laboratory investigations were performed, which revealed raised WBC count, ESR, and CRP. Radiologic co-relation was done by plain radiograph, ultrasonography, CT scan, and MRI. Plain radiograph findings were insignificant, whereas USG revealed a heterochronic collection in the iliac muscle with bulky right iliacus. CT scan of the whole spine showed numerous intercommunicating paraspinal, gluteal, and intraabdominal collections. MRI of the lumbosacral spine revealed multiple peripherally enhancing multiloculated collections compressing the cauda equina roots. These favored the diagnosis of Iliopsoas abscess. From the history of sudden neurological deterioration, saddle anesthesia, and bladder and bowel involvement despite conservative management, the final diagnosis of lower motor neuron paraparesis with cauda equina syndrome was made.

Management of iliopsoas abscess requires the drainage of the abscess along with appropriate antibiotics empirically or as per culture and sensitivity reports.¹ Cauda equina syndrome needs urgent surgical intervention by decompression of the thecal sac and nerve roots.²⁵ In our case emergency posterior decompression by unilateral laminectomy with drainage of pus was performed. And post-operatively intravenous antibiotics were given according to the culture sensitivity report, with satisfactory clinical outcome.

7 Conclusion

Iliopsoas abscess may rarely extend to the epidural space causing surgical emergency of cauda equina syndrome, which can present in various combination of lower backache with or without radiculopathy, saddle anesthesia, asymmetric motor weakness of lower limbs, and bowel/bladder dysfunction. Pyogenic organisms may be more likely to have hyperacute presentations compared to tuberculosis due to their increased virulence. Urgent surgical decompression of nerve root and evacuation of pus followed by culture and sensitivity report –guided antibiotic therapy can yield satisfactory outcome in these patients who present with cauda equina syndrome.

Ethical review committee statement

Not applicable.

Consent to participation

Not applicable.

Financial support and sponsorship

No any.

Informed consent

Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.

Authors contribution

A. R. - Planning of study, data management, writing and revising the manuscript.

S. K. B. - Data management, manuscript preparation.

V. V. - Data management, manuscript preparation.

P. K. - Revising the manuscript.

Q. A. - Revising the manuscript.

B. S. - Planning of study, revising the manuscript, and a corresponding author.

Ethical clearance

Intuitional ethical committee had approved the study (retrospective, case report) for paper publication. A copy of the ethical clearance is available for review by the Editor-in-Chief of this journal on request.