Retroperitoneal abscess formation is a rare complication following invasive abdominal procedures and even less likely to occur following spontaneous vaginal delivery.¹

Retroperitoneal abscesses pose significant risk to surrounding organs, with the kidneys, inferior vena cava (IVC), adrenal glands, neurovascular pelvic and lumbar structures potentially compromised; hydronephrosis and ureteric obstructions can lead to acute kidney injury and thromboembolism can occur secondary to IVC stasis.² Vague symptoms along with subtle clinical findings may contribute to delayed diagnosis, with lack of prompt treatment potentially leading to maternal mortality, secondary to end organ damage or sepsis.³

We present a case of a woman who re-presented after a spontaneous normal vaginal delivery with a retroperitoneal psoas abscess leading to acute kidney injury, secondary to ureteric obstruction. This was diagnosed with a computed tomography (CT) and treated with laparoscopic drainage, ureteric stenting and intravenous antibiotics.

Case

The patient was a healthy 30-year-old primiparous woman with a known history, since puberty, of slow transit constipation, which her mother and grandmother also suffered from. She had had several negative colonoscopies through her life and was able to normalise her stool pattern using bisacodyl prior to and during pregnancy. Despite this, she had an unremarkable pregnancy course and went into spontaneous labour at 39 weeks and 4 days. She had a normal course through labour and an effective epidural inserted for pain relief during the first stage of labour. She had an uncomplicated second stage of labour and proceeded to a normal vaginal birth, sustaining a second-degree perineal tear that was repaired in the delivery suite using 2-0 vicryl rapide™ sutures. A low vaginal swab was negative for Group B Streptococcus, and antibiotics were not required in labour.

On day three postpartum, the woman began experiencing severe right-sided abdominal pain. She reported unilateral flank pain, exacerbated by mobilisation. The pain radiated to lower extremities. An examination revealed a palpable mass in her right iliac fossa. A CT scan demonstrated an area of gas posterior to the caecum as well as faecal loading.  A colonoscopy was then performed, which showed a small area of pressure necrosis of the mucosa at the splenic flexure, in keeping with constipation, but no perforation. The woman was discharged on day six postpartum.

At two weeks postpartum, the woman re-presented to her obstetrician with significant facial and pedal oedema and headache. Her blood pressure was 150/80mmHg and she was re-admitted to hospital. Her serum creatinine was 115µmol/L, her uric acid was 0.45mmol/L and her spot protein to creatinine ratio was 99mg/mmol, suggestive of pre-eclampsia. She was commenced on Captopril and a renal ultrasound was performed. This revealed a right-sided hydronephrosis that had not been present on her CT scan two weeks before. She was also found to be febrile (38.5^oC) as well as having a neutrophilia (17.4 x 10^9) and an elevated C-reactive protein (317).

Diagnostic laparoscopy demonstrated a right retroperitoneal abscess lying deep into the psoas and densely adherent to the ascending colon. The abscess was then drained and dissected. There was no bowel perforation identified at laparoscopy. During the same procedure, cystoscopy and stenting were performed, revealing a tortuous ureter secondary to displacement by the abscess and reactive inflammation of the ascending colon. A 19Fr BLAKE drain was placed in the right paracolic gutter. Abscess cultures grew E. coli sensitive to Ceftriaxone.

She remained on 2g of ceftriaxone daily and subsequently had her nephrostomy tube removed on day five and her right paracolic drain removed on day six post-operatively. Unfortunately, her right flank pain recurred, as did her fevers. A CT scan performed seven days after laparoscopy revealed a discrete fluid collection anterior to the right iliacus muscle measuring 8.1×4.4×3.7cm. A return to theatre was avoided through insertion of a pigtail drain under CT guidance. This drained haemoserous fluid, with no organisms grown on culture, and remained in-situ for four days, during which time she remained afebrile with daily improvement of symptomatology. She was discharged on oral amoxicillin 14 days post-laparoscopy and more than one month postpartum.

Comment

Although psoas abscess formation is a rare occurrence, this case highlights the significant morbidity with which it may be associated. Mortality associated with psoas abscess has been reported in the literature at 2.5 per cent; however, if there is a delay in treatment, mortality rises to 18.9 per cent.^{1 4} Psoas abscesses are described as primary or secondary.^{3 5 6} Primary involves haematogenous spread from a known or, more frequently, unknown source. Outside the obstetric population it has been reported most often in intravenous drug users,⁶ the most common pathogen being staphylococcus aureus. Conversely, secondary abscess’ result from local spread of an infection, for example, from gastrointestinal, renal or musculoskeletal spread. Common organisms include E. coli, streptococcus and enterococcus.⁷

A MEDLINE search (search terms ‘psoas abscess’ and ‘vaginal delivery’) identified seven cases in the literature, with this being the first reported case in Australia. The condition was first described in 1881 by the physician Herman Mynter.⁸ The aetiology of our patient’s abscess formation is not known, given her general health, lack of co-morbidities and no history of intravenous drug use. It is unclear how a healthy patient with such an uncomplicated delivery developed a psoas abscess. In theory, infection from perineal or vaginal trauma could spread retroperitoneally and form an abscess, which may have occurred for our patient. Pudendal anaesthesia has been noted to cause a secondary psoas abscess in the literature; however, this was not used for our patient. ⁹ Another potential cause is the formation of a pelvic haematoma intrapartum, which subsequently became infected.¹⁰

Diagnosis is difficult and requires a high level of suspicion. In this case, we highlight the importance of postnatal follow up. Clinically, patients with unilateral flank pain, pain with mobilisation and radiation to lower extremities, should alert clinicians to the possibility of a psoas abscess. Threshold for imaging these patients should be low, especially if patients remain persistently febrile on antibiotics. CT scanning has been shown to be more than 80 per cent specific in diagnosing a psoas abscess and, although ultrasound has a role in diagnosis, its lower specificity can potentially hinder management decisions.^{3 4}

Even though psoas abscess as a complication of spontaneous vaginal delivery is rare, it is associated with potentially significant morbidity as well as mortality. Clinicians who encounter symptoms similar to that presented in this case, including unilateral flank pain, pain with mobilisation and radiation to lower extremities should be mindful to exclude this diagnosis. Initiation of broad-spectrum antibiotics and expedited drainage, whether under radiological guidance or laparoscopically, should be arranged if this diagnosis is made.

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