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A rare presentation of a common disease

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Q1: What are the radiographic findings (see p 662)?

The thoracic radiograph shows normal lung fields with subtle linear lucencies along the superior left cardiac border and in the paratracheal region consistent with a pneumomediastinum. The heart and trachea are outlined in the radiograph because air is radiolucent and it tracks along the fascial planes. There is also free intraperitoneal air most evident below the right hemidiaphragm. The abdominal radiograph shows similar radiolucent tracks outlining the psoas muscles. The abdominal computed tomogram confirms the presence of retroperitoneal air with extensive inflammation.

Q2: What is the most likely diagnosis?

Pneumomediastinum is usually caused by a perforation of the upper aerodigestive tract but it is rarely due to a leak from the infradiaphragmatic intestine. Perforation of any part of the aerodigestive tract may be traumatic, spontaneous, or iatrogenic in origin. The latter includes endoluminal or percutaneous procedures and positive pressure ventilation of the respiratory tract.

The presence of pneumomediastinum, pneumoperitoneum, and retroperitoneal inflammation suggests a perforation of the lower gastrointestinal tract. Without a history of recent trauma or invasive procedure, a spontaneous perforation of a colonic lesion into and posterior to the peritoneum is the most likely diagnosis. Diverticular disease is the most common cause of this unusual combination, although carcinoma and ulcerative colitis may rarely present this way.

Q3: What are the treatment options?

The decision between performing a primary anastomosis or bowel exteriorisation after resecting the affected colon depends on the extent of faecal contamination. The risk of anastomotic failure is high in the presence of sepsis and malnutrition. An ileostomy with mucous fistula formation for right sided and Hartmann's procedure for left sided colonic perforations are preferable to primary anastomosis if there is extensive soiling.

Attention should be paid to eliminating abdominal and mediastinal sepsis postoperatively. This requires intraoperative abdominal lavage, postoperative respiratory physiotherapy and broad spectrum intravenous antibiotics until bacterial sensitivities are available. Nutritional support is also essential in the perioperative period to reverse the catabolic state.

Localised abscess formation without septicaemia after a sealed colonic perforation may be treated conservatively. This includes adequate percutaneous drainage of the abscess, antibiotic therapy, oral abstinence, and parenteral nutrition to reduce colonic loading. Failure to progress or clinical deterioration mandates early surgical intervention.

This patient underwent a laparotomy where an abscess cavity was found in the left paracolic gutter in association with diverticulitis of the descending colon. The abscess cavity extended along the left psoas muscle cranially towards the mediastinum and caudally into the thigh. Crepitus was felt along the left psoas muscle. A Hartmann's procedure was performed due to the extent of the sepsis. Histological examination of the resected specimen confirmed the presence of a perforated colonic diverticulum. The patient subsequently died from multiorgan failure.

Learning points

  • Colonic perforation occurs in about 15% of patients with complicated diverticular disease and is usually intraperitoneal.

  • Retroperitoneal diverticular perforation is rare and is suggested by the presence of pneumomediastinum, subcutaneous emphysema, and/or pneumothorax.

  • Resection of the perforated bowel with exteriorisation is usually required. Occasionally non-operative management is possible if the sepsis is contained but surgery becomes mandatory with clinical deterioration.

Discussion

Colonic diverticular disease is common and its complications can cause significant morbidity and mortality. Up to a quarter of patients with acute diverticulitis will require surgery and about 15% of these are due to colonic perforation.1 Most diverticula perforate only into the peritoneal cavity resulting in a localised pericolic abscess. This may subsequently fistulate into the bladder, adjacent bowel, or cutaneously. However generalised peritonitis supersedes if the sepsis is not contained with a high risk of septic shock and multiorgan failure. The mortality following a Hartmann's procedure for a left sided perforation is 12% compared with 28% for peritoneal drainage alone, with or without oversewing the mucosal defect.2

In contrast retroperitoneal colonic perforation due to diverticular disease is rare.3 4 The descending rather than sigmoid colon is more likely to perforate this way because the former is fixed in the retroperitoneum. Furthermore since diverticula form where the blood vessels penetrate the bowel wall and because the sigmoid colon has a free mesentery, a diverticulum at this site will generally perforate into the peritoneal cavity.

Signs of peritonitis may be absent if the sepsis is confined to the retroperitoneum and this can lead to a diagnostic delay. Indeed the sepsis may track downwards and present as a chronic abscess involving a hip joint5 or as thigh pain.6 In addition the high intra-abdominal and colonic pressure can lead to interstitial tracking of air upward to areas of low pressure resulting in pneumomediastinum.7 Subsequent rupture into the pleural cavity and subcutaneous tissue results in a pneumothorax8and surgical emphysema respectively.4

The possibility of a colonic perforation should be considered in patients who present with pneumomediastinum, pneumoperitoneum, and retroperitoneal inflammation. While an anteroposterior thoracic radiograph may miss half of the cases of pneumomediastinum, a lateral view usually demonstrates retrosternal air. Abdominal and thoracic computed tomograms may help to confirm the diagnosis.

Final diagnosis

Colonic diverticular perforation resulting in pneumomediastinum, retroperitoneal inflammation, and pneumoperitoneum.

References

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