PI is not a diagnosis in itself, but a radiological finding secondary to one of numerous causes and has a range of clinical outcomes.
In the context of non-specific abdominal symptoms, the initial radiological findings and associated pneumoperitoneum may mimic an acute abdomen representing a diagnostic challenge for the surgeon. An accepted classification has been to divide PI into a primary type (15%) and those secondary to a pathological process (85%).3
This classification has been challenged throughout the literature as the intramural gas is always secondary to an underlying pathology in some form. Over the past 60 years, as the accepted theories of pathogenesis have emerged, the primary or benign form is considered, in the majority of cases, to exist secondary to pulmonary disease.
The pulmonary theory received initial scepticism following its development during the early 1960s. As numerous case series were published linking cases of PI with a common history of allergy and asthma, Keyting et al5
presented a case series of PI associated with pulmonary disease and was the first to apply the now established theory that alveolar rupture could result in a pneumomediastinum; they suggested the potential existed for gas to then dissect via several routes, including a peri-vascular route, to the submucosal and subserosal layers of the mesocolon. Well-recognised pulmonary associations include asthma, cystic fibrosis, chronic obstructive pulmonary disease, barotrauma, thoracic injury and following lung transplantation.
Significantly, Doumit et al6
reported an isolated case of uncomplicated PI in a 66-year-old woman suffering from chronic bronchiectasis, which resolved after conservative management. This association had not previously been reported within the English literature. In our case, the patient had a history of bronchiectasis of unknown aetiology, characterised by a chronic productive cough and was under long-term respiratory review. She had reported no recent change in symptom severity, which may have led to the accumulation of intramural gas. Ten years previously she had undergone a right lower lobectomy, indicating the past severity of her symptoms and failure of medical management.
Two features of our case deserve further discussion: the recurrence of symptoms leading to a diagnosis of CMI and the evaluation of a ‘medical’ pneumoperitoneum.
Following the recurrence of symptoms, further imaging was undertaken with the findings demonstrating the importance of re-evaluating the diagnosis after failure of conservative management. Evidence of PI is often identified following presentation with subacute abdominal symptoms. In this case, chronic SMA ischaemia had led to PI with pneumoperitoneum. Mesenteric ischaemia is an uncommon cause of abdominal pain, accounting for fewer than 5% of intestinal ischaemic events, and producing the well-defined symptoms of postprandial abdominal pain and food aversion leading to weight loss, which become evident when two out of the three splanchnic vessels are involved7
; PI, if present, is one of the few imaging signs to occur in CMI.
PI is one of many non-surgical causes of intraperitoneal free gas. With 90% of non-iatrogenic pneumoperitoneum indicating a visceral perforation,8
the remaining proportion may be regarded as ‘spontaneous’ or ‘medical’ resulting from postoperative, thoracic, abdominal or gynaecological causes.9
Intra-abdominal free gas is an uncommon complication evident in up to 10% of patients with small bowel pneumatosis and 2% with large bowel pneumatosis.1
Symptoms occurring in association with PI and pneumoperitoneum require careful analysis with exclusion of either an ischaemic event or perforation.
An awareness of the pathogenesis of benign PI and other ‘non-surgical’ causes of pneumoperitoneum empowers the surgeon to pursue a conservative approach with exploratory surgery indicated only in highly selected cases not responding to non-operative management.
Of significance in our case, the patient had not recently received steroid treatment for her bronchiectasis. In the context of immunosuppressive treatment, the surgeon must be alert to the risks of conservatively managing those presenting with pneumoperitoneum and a paucity of clinical findings since the signs of peritonism may be masked. In these situations, and when hollow organ perforation cannot be excluded, many would advocate early exploratory laparotomy to exclude the presence of bowel necrosis or perforation.10
In our case, the patient responded well to the conservative approach involving bowel rest, TPN and intravenous metronidazole.
An examination of factors independently associated with a decision to adopt a surgical approach and a greater mortality, in cases of PI, was undertaken by Greenstein et al11
In their review of 40 patients with a retrospective diagnosis of PI, they showed those 60 years old or over, and either the presence of vomiting or white cell count greater than 12 × 109
, were most likely to undergo surgery, while sepsis was the sole independent risk for death. A single-centre study of 27 patients over a 1-year period, of which 16 underwent surgery, considered surgical management and predictors of outcome.2
Those showing the greatest benefit from surgery demonstrated abdominal symptoms associated with acidosis and hyperamylasaemia; however, eight of the patients with ischaemic bowel and PI had 75% mortality despite their surgery. No clear algorithm for surgical management has yet been accepted.
- PI is an unusual radiological finding, although not a diagnosis in itself. It is reported in association with numerous underlying pathologies from the benign to life-threatening.
- Surgeons must remain alert to the numerous medical causes of intra-abdominal free gas in the adult and the appropriateness of a conservative approach in benign causes. Equally, it is imperative to identify those patients with PI, with or without complications, with underlying pathologies requiring urgent intervention.
- No algorithm exists to dichotomise patients into conservative and surgical management. However, before attributing the PI to a benign process, urgency must be established based upon symptom characteristics, radiological features, including portal venous gas and pneumoperitoneum, lung pathology, vascular supply to the involved bowel segment and surgical history.
- Mesenteric ischaemia is an uncommon cause of abdominal pain accounting for fewer than 5% of intestinal ischaemic events.
- PI, if present, is one of the few imaging signs to occur in CMI.