Pediatr Radiol (1998) 28: 312±314 Ó Springer-Verlag 1998

Jane E. Benson Eric D. Strauch

Received: 26 June 1997 Accepted: 21 November 1997

)

J. E. Benson ( ) Division of Pediatric Radiology, Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Hospital, 601 N. Wolfe Street, Baltimore, MD 21287, USA

Retropsoas hernia as a cause of chronic abdominal pain: CT diagnosis

Abstract Congenital retropsoas small bowel herniation is reported as the cause of long-standing recurrent abdominal pain in a teenage girl. Knowledge of this entity is important for differential diagnosis of abdominal pain, mass, or retroperitoneal gas and fluid, and for avoiding complications of percutaneous renal interventions.

E. D. Strauch1 Division of Pediatric Surgery, Johns Hopkins Hospital, Baltimore, Maryland, USA Present address: 1 Pediatric Surgery, N4E37 University of Maryland Hospital, 22 S. Greene Street, Baltimore, MD 21201, USA

Introduction Wherever there are congenital or acquired defects in the peritoneal lining of the abdominal wall or mesentery, mobile bowel or omentum can herniate and sometimes strangulate. Symptoms can be protean, leading caregivers either to discount the patient's complaints or to initiate costly and repetitious work-ups. The pathology in this puzzling case proved to be an internal hernia not previously described in the literature.

Case report A 15-year-old girl with a 12-year history of recurrent abdominal pain and vomiting underwent elective upper gastrointestinal exam and small-bowel follow-through (SBFT) in February, 1995, which

showed a 6-cm mass effect compressing the small bowel in the left pelvis (Fig. 1) without obstruction. Coffee-ground emesis a few days later prompted admission. CT scan showed herniation of a loop of small bowel lateral and posterior to the left psoas muscle at the level of L4 and extending into the pelvis (Fig. 2). There was no strangulation, obstruction, or other mass. At surgery, a true peritoneal defect 2.5 cm long was found along the lateral border of the psoas muscle just superior to the iliac crest. Small bowel had herniated through this defect to a depth of 4 cm. The bowel was moved back to the peritoneal cavity, and the defect was closed. There was no malrotation or other abnormality. The patient recovered uneventfully and had no recurrence of symptoms at 1-year follow-up.

Discussion An electronic search of imaging and surgical literature and a review of standard reference books did not con-

313

tain a description of a retropsoas hernia. This hernia differs from the classically described forms of lumbar hernia involving Grynfelt's and Petit's triangles, where bowel passes through the thoracolumbar fascia and causes a bulge at the skin surface. Moreover, these triangles are bounded by latissimus dorsi, serratus anterior and quadratus lumborum muscles; there is no mention of the psoas muscle in these descriptions [1±3]. In the current example, the bowel lies deeper and more medial in the back and is still contained within the thoracolumbar fascia. The non-obstructing mass effect that persisted on conventional SBFT despite palpation was thought to be possibly in the bowel (duplication cyst, hematoma, leiomyoma), in the mesentery (mesenteric cyst, lymphoma), or due to an ectopic kidney. Psoas pathology (hematoma, abscess) was not seriously entertained due to a lack of clinical symptoms. In retrospect, one can see how paddle palpation might not have affected such a retroperitoneal pathology, but it is difficult to explain how the herniated bowel loops may have been completely effaced and yet non-obstructive, unless herniation was intermittent and the timing of the film was serendipitous. The CT scan was obtained when the patient was seriously symptomatic, and showed the pathology clearly. The CT finding of gas and fluid adjacent to the psoas muscle could potentially be a diagnostic dilemma. At the level of the kidneys, the psoas muscle forms the pos-

terior boundary of three extraperitoneal compartments: the anterior and posterior pararenal spaces and the perirenal space, divided by the peritoneum, the lateroconal fascia, and the anterior and posterior renal fasciae [4]. Inferior to the kidneys, the spaces are less clearly demarcated, and pathologic processes move more freely between them. A pelvic infection could result in gas and fluid migrating into the posterior pararenal space in a way that could simulate a retropsoas hernia. Pancreatitis, dissecting pancreatic abscess or pseudocyst, or a psoas abscess might show a similar image or even pathology around the psoas muscle itself. To make the correct diagnosis prior to laparotomy, CT images were essential for differentiating tubular bowel loops from extraluminal gas and fluid and recognizing their posterior, retropsoas position.

Fig. 1 SBFT, 45 min film. Contrast opacifies the small bowel and the colon with no evidence of obstruction, despite the mass effect (arrowheads) on the left Fig. 2 Transverse CT scans of the abdomen, with oral and intravenous contrast. Small bowel (arrow) lies posterior to the left psoas muscle, medial to the contrast-filled descending colon. Scans are 1 cm superior (a) and 2 cm inferior (b) to the left iliac crest, showing the distribution of the hernia. This suggests that the ªmassº seen on the SBFT was actually the left psoas muscle

2a

1

2b

314

Advance knowlege of variant anatomy in a patient becomes very important when contemplating interventional radiologic procedures. Though medial deviation of the ascending and descending colon is most often associated with renal absence or malposition [5], a nearretrorenal position of the descending colon can be seen as a normal variant due to a more posterior fusion of the anterior renal fascia with the lateroconal fascia,

especially in children who have very little retroperitoneal fat (personal observation). Such bowel placement near the kidney could potentially interfere with interventional procedures involving the kidney, such as placement of a percutaneous nephrostomy or biopsy needle [6]. Since the defect described in the present case could be anywhere along the psoas reflection, a retropsoas hernia could also migrate into the perirenal region.

References 1. Zarvan NP, Lee FT, Yandow DR, Unger JS (1995) Abdominal hernias: CT findings. AJR 164: 1391±1395 2. Nyhus LM, Condon RE (1995) Hernia. Lippincott, Philadelphia

3. Alfisher MM, Larsen CR, Palmer LF (1995) Lumbar herniation of the spleen. Abdom Imaging 20: 446±8 4. Meyers MA (1988) Dynamic radiology of the abdomen. Springer, New York, pp 179±278 5. Meyers MA (1988) Dynamic radiology of the abdomen. Springer, New York, pp 300±317

6. Ferral HF, Stackhouse DJ, Bjarnason H et al (1994) Complications of percutaneous nephrostomy tube placement. Semin Intervent Radiol 11: 198±206