British Journal of Radiology 75 (2002),381-383 © 2002 The British Institute of Radiology
Small bowel obstruction due to incarcerated sciatic hernia: ultrasound diagnosis
P-C Yu, MD
1
S-F Ko, MD
1
T-Y Lee, MD
1
S-H Ng, MD
2
C-C Huang, MD
1 and
Y-L Wan, MD
2
1 Department of Radiology, Chang Gung University, Chang Gung Memorial Hospital at Kaohsiung, 123 Ta-Pei Road, Niao-Sung Hsiang, Kaohsiung Hsien 833 and 2 Department of Radiology, Chang Gung University, Chang Gung Memorial Hospital at Linkou, 5 Fu-Shing Street, Kwei Shan, Tao Yuan, Taiwan
Correspondence: Sheung-Fat Ko, MD
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Abstract
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A 71-year-old woman presented with vomiting, abdominal pain and vague right gluteal discomfort. Abdominal ultrasound showed ascites and dilated small bowel loops with peristaltic movement, while transgluteal ultrasound revealed entrapped ascites beneath gluteal muscles and an oedematous, immobile bowel loop trapped between the sacrum and iliac bone with barely visible colour Doppler flow suggestive of an incarcerated sciatic hernia. CT demonstrated similar findings and subsequent surgery confirmed the diagnosis. To our knowledge, this is the first report of a pre-operative diagnosis of incarcerated sciatic hernia on ultrasound.
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Introduction
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Sciatic hernia is an unusual cause of small bowel obstruction (SBO). However, unlike other causes of SBO such as adhesions, in which conservative treatment and expectant observation may be appropriate, SBO owing to an incarcerated sciatic hernia requires immediate surgery as the incidence of strangulation and bowel gangrene is high, even if symptom duration prior to patient presentation is short [1–4]. Since clinical recognition of SBO owing to sciatic hernia can be difficult, various imaging modalities have been applied in diagnosing this disorder [2–5]. Herein we describe a rare case of an incarcerated sciatic hernia that was clinically overlooked, whilst ultrasound offered a rapid and precise pre-operative diagnosis. In addition, the importance of colour Doppler studies in surgical planning is emphasized.
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Case report
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A 71-year-old woman with a 5-year history of cirrhosis presented to our emergency department owing to abdominal cramps and vomiting for 1 day. Physical examination revealed abdominal distension with diffuse tenderness and decreased bowel sounds. Laboratory findings were unremarkable except for mildly elevated serum glutamic oxaloacetic transaminase and glutamic pyruvic transaminase levels. Plain abdominal radiography showed gaseous distension of the small bowel and ascites. Endoscopy revealed multiple areas of gastric erosion. Abdominal ultrasound revealed a mildly cirrhotic liver, borderline splenomegaly, ascites and dilated fluid filled bowel loops with increased peristaltic movement suggestive of SBO. During the ultrasound examination the patient complained of deep-seated right pelvic or gluteal discomfort. She was asked to lie in a prone position and asymmetric bulging of her right buttock was then recognized. Transgluteal ultrasound (Figure 1
). revealed fluid accumulation beneath the right gluteal muscles and a segment of fluid filled, oedematous immobile bowel loop entrapped between the iliac bone and sacrum, suggestive of a sciatic hernia. Colour Doppler study of the oedematous bowel wall showed absence of blood flow suggestive of incarceration with bowel ischaemia. CT (Figure 2) showed similar findings. Emergency surgery via a transabdominal approach was performed. At surgery a strangulated short segment of herniated distal ileum through the right greater sciatic foramen above piriformis was found. Entrapped ascites in the right subgluteal region was also noted. A segmental resection of the ileum, end-to-end anastomosis and closure of the defect at right sciatic foramen was performed. Pathological examination of the surgical specimen showed haemorrhagic, inflammatory and necrotic changes of the ileal bowel wall. The patient recovered uneventfully, was discharged 10 days later and remained well at 1-year follow-up.
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Figure 1. Transgluteal ultrasound scan showing fluid accumulation in the right subgluteal region and an oedematous dilated bowel loop (long arrow) entrapped between the inferior border of the iliac bone (short black and white arrows) and lateral margin of the sacrum (arrowheads).
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Figure 2. CT image showing incarcerated bowel loop (arrow) through the right sciatic foramen, similar to Figure 1 , and entrapped ascites in the right subgluteal region.
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Discussion
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SBO is a commonly encountered problem in an emergency department. In a Mayo clinic series, of 289 patients and 314 operations for SBO, adhesions (49%) and neoplasms (16.2%) were the most common causes. Hernias were the third most commonly encountered aetiology contributing 15% of cases, but less than one-third of these were internal hernias related to entrapment of the small intestine in mesenteric defects [1]. Sciatic hernias are one of the most uncommon forms of internal hernia and only 53 cases have been documented [2–4]. Owing to a great variety of clinical presentations that depend on hernia content, this uncommon disease is difficult to diagnose [2–4]. Sciatic hernia of the small bowel may lead to SBO presenting with abdominal pain and intestinal distension, while nausea and vomiting may occur when complicated with incarceration or strangulation. Hernia of the ureter or bladder into the sciatic foramen will manifest as urinary tract symptoms. Other contents like colon, omentum, fallopian tubes, ovary and Meckel diverticulum have also been described. On rare occasions, sciatic hernias may mimic sciatica, with back pain or leg pain owing to compression of the sciatic nerve [2–4]. A careful physical examination of the buttock may reveal a tender or non-tender gluteal mass. However, most emergency physicians habitually perform physical examination on the bedside with the patients in the supine position. Therefore, as in this case, unless deliberately specified by the patient, the gluteal lesion is easily overlooked.
Plain abdominal radiography is diagnostic in about 50–60% of cases of SBO, equivocal in about 20–30% of cases and normal or misleading in 10–20% of cases, regardless of aetiology [6–8]. Yet identification of sciatic hernia on plain radiography is not easy [2–5]. Barium studies may demonstrate persistent outpouching of bowel loops through the sciatic foramen 2–5]. However, barium filling of the close-loop, as in incarcerated or strangulated sciatic hernias, is hampered. In addition, barium studies of SBO are time consuming and the barium column may be diluted by intraluminal fluid obscuring the detail of obstruction. Sciatic hernia diagnosed by herniography has been reported but this method is invasive [3]. CT has been found useful in patients with delineation of SBO owing to sciatic hernia [2–4], but a rational guideline for its use in SBO has not been fully developed [7]. It is reliable for diagnosing high grade SBO but shows a relatively low sensitivity in cases of low grade obstruction. Moreover, CT may not be a practical screening tool for all patients with non-specific abdominal pain or vomiting [7, 8]. Ultrasound is a versatile tool that can be performed at the bedside in the emergency department. Although abundant gas may prevent satisfactory examination of the abdomen, using fluid filled bowel loops as an acoustic window or performing a meticulous examination through the flank may show the presence, level and cause of SBO [8, 9]. Ultrasound observation of peristaltic movement is easy allowing differentiation of mechanical obstruction or paralytic ileus. In a series of 54 adult cases, the diagnostic rate of SBO on ultrasound was 89%, whilst in another series of SBO owing to intussusception in paediatric patients, the detection rate was 84% [8, 9]. However, less than 20% of underlying aetiologies of SBO can definitively be recognized [9]. To our knowledge, this is the first report of a pre-operative diagnosis of incarcerated sciatic hernia on ultrasound.
Symptomatic sciatic hernias should be operated on as soon as possible. A transabdominal approach is recommended in patients who present with SBO, especially when incarceration or strangulation is suspected. On the other hand, a less invasive transgluteal approach may be used when the herniated segments appear viable and reducible [2–4]. Therefore, pre-operative determination of viability and reducibility is important for surgical planning. Colour Doppler demonstration of blood flow in bowel obstruction owing to intussusception has been reported as a promising predictor of bowel viability and hydrostatic reducibility, and the absence of blood flow on Doppler scanning is highly suggestive of irreducibility and bowel ischaemia [9, 10]. As illustrated in our case, colour Doppler ultrasound was useful in depicting the absence of blood flow in the strangulated sciatic hernia. In addition, reduction under ultrasound guidance can be tried, though not performed in our case owing to the presence of entrapped ascites and the suspicion of strangulation. Indeed, the ultrasound findings that led to an emergency transabdominal laparotomy in this patient proved correct.
In conclusion, the diagnosis of an incarcerated sciatic hernia is difficult, but awareness of this unusual entity in SBO patients, and examination of gluteal regions, make it possible. Ultrasound is useful in establishing the diagnosis of sciatic hernia and colour Doppler studies provide information about the viability of the herniated bowel that is important for surgical planning.
Received for publication November 2, 2001.
Accepted for publication November 30, 2001.
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Abstract
Introduction
