Retroperitoneoscopic drainage of cryptogenic psoas abscess

Abstract

Psoas abscess is a rare and occasionally life-threatening condition. In the past, the major cause of psoas abscess was a descending infection originating from spine tuberculosis (Pott’s disease). Subsequently, secondary infection from spondylodiscitis or Crohn’s disease has become the prevalent aetiology. Conventional treatment ranges from antibiotic therapy alone to CT-guided and/or surgical drainage. We present the case of a 67-year-old man with a complex history, including pneumonia, sepsis and previous muscle-skeletal trauma. The patient subsequently developed a psoas abscess that was successfully treated with a minimally invasive retroperitoneoscopic approach and antibiotics. Blood cultures and pus yielded Gram-positive Streptococcus sp, and transesophageal echocardiography identified endocarditis as a possible source of sepsis. Postoperative clinical course was complicated by recurrent sepsis that required a change of antibiotic therapy. The patient was eventually discharged to rehabilitation care without further complications. The retroperitoneoscopic approach is safe and effective for the treatment of cryptogenic psoas abscess.

Background

Psoas abscess, a collection of pus in the iliopsoas compartment, was first described by Mynter in 1881 as psoitis.¹ This condition is classified as primary or secondary depending on the likely etiopathogenesis. Low back pain, limited range of movement of the lower limb with hip flexion contracture and fever are the most frequent symptoms, but such a classic triad is present only in 30% of cases.² Furthermore, a non-specific clinical presentation can be responsible for the diagnostic delay and lead to fatal complications.

CT and/or MRI are essential for diagnosis and therapeutic decision-making.³ Treatment of iliopsoas abscess consists of drainage of the purulent collection combined with appropriate antibiotic therapy. Debate still exists as whether the initial therapy of choice should be CT-guided or surgical drainage. In recent years, the role of mini-invasive surgery has emerged as a safe and effective therapeutic option.

Case presentation

A 67-year-old obese white man, previously admitted to another hospital for community-acquired right pneumonia, was transferred to our intensive care unit for acute respiratory failure. During the previous hospitalisation, the patient had been treated with intravenous levofloxacin, 500 mg every 12 hours.

On admission, his body temperature was 38.4°C, respiratory rate 20/min, heart rate 96 beats/min, blood pressure 120/70 mm Hg and oxygen saturation 94% on oxygen 2 L/min. The arterial gas analysis showed pO₂ 86.3 mm Hg, pCO₂ 33 mm Hg and pH 7.5. Body mass index was 34. Past medical history included blood hypertension, obstructive sleep apnea, chronic obstructive pulmonary disease, coronary artery disease, type II diabetes, dyslipidaemia, previous radical prostatectomy, bilateral inguinal hernia repair, repair of recurrent left groin hernia and bilateral hip replacement. In addition, the patient referred a recent accidental fall that occurred at home, where he lived alone, with a prolonged stay on the ground. Age-related Charlson Comorbidity Index (CCI) was 7, and American Anesthesiological Association (ASA) Score was 3. Physical examination was unremarkable, except for a large left inguinoscrotal hernia. Laboratory findings showed white cell count 13.30×10⁹ L (4 to 11×10⁹ L), platelets 611×10⁹ L (150–450×10⁹ L), C-reactive protein (CRP) 14.4 mg/dL (<mg/dL) and procalcitonin 0.6 ng/mL (<0.5 ng/mL). The patient required orotracheal intubation for progressive dyspnoea. Subsequently, based on the finding of Streptococcus intermedius in blood cultures, antibiotic therapy was replaced with linezolid, 600 mg every 12 hours.

Investigations

A transthoracic cardiac ultrasound, performed to rule out endocarditis, was normal. Due to progressive deterioration of the clinical status with persistent fever, respiratory failure and the onset of low back pain extended over the left thigh, the patient underwent a thoracoabdominal contrast-enhanced CT scan that revealed bibasilar pulmonary atelectasis and an enlargement of the left psoas muscle compartment with wall enhancement consistent with a multiloculated abscess. The collection extended through the left retroperitoneal adipose tissue, laterally to the psoas muscle, posteriorly into the gluteal region and anteriorly into the left groin hernia sac (figure 1); a small right quadriceps abscess (2×1 cm) was also described. Based on the morphology and extension of the abscess, a CT-guided percutaneous drainage was considered inappropriate and therefore we opted for a retroperitoneoscopic surgical approach.

Figure 1.

(A) CT scan showing multiloculated abscess with wall enhancement of the left psoas compartment. (B) The purulent collection extends into the left retroperitoneal adipose tissue and inferiorly up to into the ipsilateral gluteal region.

Differential diagnosis

The classic triad of presentation, including fever, pain and limited range of movement of the hip joint, is pathognomonic of psoas abscess. The differential diagnosis should take into account other conditions, such as lumbar spine trauma, radiculitis and lombosciatalgia, spondylodiscitis, renal colic, pyelonephritis, hip arthritis and aortoiliac aneurysm.⁴ CT scan, blood and pus cultures and transesophageal echocardiography were essential for the diagnosis.

Treatment

The operation was performed under general anaesthesia. The patient was placed in the full right flank position. Under ultrasound guidance, an optical trocar was placed in the left lumbar region on the posterior axillary line, cranial to the iliac crest, in the context of the abscess collection (figure 2). No balloon expansion was necessary to access the retroperitoneal space because of the extensive extraperitoneal spreading of the pus collection. About 200 mL of purulent material was rapidly evacuated. CO₂ pneumoretroperitoneum was then set at a pressure of 8 mm Hg, and a 30° scope was introduced in the cavity abscess. Through an additional 10 mm trocar placed on the midaxillary line, below the costal margin, blunt dissection and debridement were performed to remove all necrotic material, and the cavity was finally irrigated with saline and diluted Betadine solution. At the end of the procedure, two 24 Fr drains, one posterior, deeply into the cavity and another more anterior were placed (figure 3). A double-lumen Salem tube was also placed parallel to the anterior drain to allow cavity irrigation.

Figure 2.

Patient position and anatomical landmarks for the retroperitoneoscopic access. (Figure drawn by Dr Daniele Bernardi.). CM, coastal margin; IC, iliac crest. *Middle axillary line, **posterior axillary line.

Figure 3.

Introduction of the first trocar in the left lumbar region and pus evacuation (A); blunt dissection and debridement of the retroperitoneal space (B); irrigation and suction of necrotic material (C) and placement of drains (D).

Outcome and follow-up

Postoperative course was complicated by the onset of sepsis on the fifth postoperative day. A CT scan showed the persistence of the right basal pulmonary consolidation and the appearance of left upper lobe nodular infiltrates; the retroperitoneal cavity was almost completely cleared (figure 4), but the abscess at the level of the right quadriceps increased in size (4×3 cm). This required surgical drainage under local anaesthesia. Gemella morbillorum and Streptococcus cristatus were identified on cultures obtained from both the psoas and the thigh abscess. A transoesophageal echocardiography was then performed and showed the presence of aortic valve vegetations consistent with endocarditis. Antibiotic therapy was switched to ampicillin, 3 g every 6 hours for 4 weeks, and gentamicin, 240 mg daily for 2 weeks. The patient’s general conditions gradually improved with resolution of fever, and normalisation of white cell count and CRP levels. Drains were removed on postoperative day 12. The patient was then discharged to rehabilitation care without further complications. The patient is alive and free of recurrence at 3-month follow-up, and a transthoracic cardiac ultrasound showed the resolution of the endocarditis.

Figure 4.

CT scan on postoperative day 3 (A, B) showing almost complete resolution of the psoas abscess.

Discussion

We initially hypothesised that the abscess could have been secondary to infection of a post-traumatic haematoma in the iliopsoas retroperitoneal compartment. However, persistent sepsis after surgical drainage, the appearance of a contralateral thigh abscess, the multiple pulmonary infiltrates, the signs of endocarditis at transoesophageal echocardiography and the evidence of Gram-positive streptococci on blood cultures and pus indicated that the hypothesis of cardiogenic septic embolism was more plausible. In a systematic review and meta-analysis, the pooled prevalence of septic embolism in patients with infective endocarditis was 25%.⁵

Iliopsoas abscess is a rare clinical condition. In the past, the major cause of psoas abscess was a descending infection originating from spine tuberculosis (Pott’s disease). More recently, secondary infection from spondylodiscitis or Crohn’s disease has become the prevalent aetiology. Primary iliopsoas abscess is attributed to haematogenous spread of an occult infectious process, with the most common causative agent being Staphylococcus aureus, and trauma with haematoma formation may predispose to abscess development.⁶

CT is the gold standard for diagnosis of psoas abscess with almost 100% high sensitivity rate.³ Transesophageal echocardiography is superior to transthoracic echocardiography for detection of endocardial vegetations, with a sensitivity of 90–100% and a specificity of 90%.⁷

Broad-spectrum antibiotic therapy, traditionally the first-line therapeutic option, is likely to fail as the sole treatment in patients with large and multiloculated psoas abscess. Moreover, when a primary psoas abscess is suspected based on CT findings, presence of endocardial vegetations, and isolation of Gram-positive pathogens, a targeted antibiotic treatment should be initiated.

In most patients, drainage is mandatory, but there is no consensus regarding the choice of percutaneous CT-guided versus surgical approach. Percutaneous drainage can be performed under local anaesthesia at bedside, but is associated with a 60% recurrence rate and need for repeat drainage and/or surgical treatment.⁸ However, surgical therapy has often be reserved to failures of percutaneous drainage or to patients with coexisting disease, such as Crohn’s disease, that may require definitive treatment.^{9 10}

Hsieh et al¹¹ and Baier et al¹² advocated open surgical drainage as first-line treatment to guarantee complete abscess evacuation and to prevent recurrence and sepsis-related complications. A minimally invasive transperitoneal or extraperitoneal approach could represent a valid alternative to open surgery and may provide shorter hospital stay and superior patient comfort.^13–16 Katara et al¹⁷ first described a retroperitoneoscopic drainage of psoas abscess in a child, and two case series^{18 19} found this approach safe and effective in patients with psoas abscess secondary to spondylodiscitis. To the best of our knowledge, this is the first reported case of primary iliopsoas abscess treated by a retroperitoneoscopic approach. Considering the patient's comorbidities (age-related CCI was 7) and the high operative risk (ASA Score was 3), the minimally invasive surgical strategy seemed the most appropriate for this frail, elderly individual.

Learning points.

• Psoas abscess is rare, and pathognomonic symptoms can be obscured by a complex clinical presentation.

• CT scan is the gold-standard test for diagnosis and is essential to plan the most appropriate treatment.

• The findings of endocarditis and Gram-positive species on blood and pus cultures support the hypothesis of septic embolisation and guide the antibiotic treatment.

• The retroperitoneoscopic approach is safe and effective for the treatment of cryptogenic psoas abscess.

Patient’s perspective.

It was tough staying in the hospital for such a long time and suffering from exhausting fever attacks. I still remember the shaking chills and profuse sweating that accompanied for several days the course of the disease. Instead, the operation went smoothly and painless. I am very grateful to all doctors and nurses who took care of me. My wife passed away a few years ago, I do not have relatives, I live alone, so I could really appreciate the great care I received in your hospital. You made me comfortable and not feeling alone! Thanks so much, I will never forget what you have done for me!!!