Читать книгу Clinical Pancreatology for Practising Gastroenterologists and Surgeons - Группа авторов - Страница 83

CECT can be used to diagnose pancreatic necrosis, which is associated with higher mortality and morbidity because it is patients with necrosis who most commonly develop persistent organ failure. Necrosis is best recognized by liquefaction, and is usually identified two to three days after onset of clinical symptoms [28]. Extrapancreatic necrosis (EXPN) may also be seen as a result of pancreatic enzymes extravasation into the tissues surrounding the pancreas. CECT shows extrapancreatic morphological changes exceeding fat stranding, with complete enhancement of the pancreatic parenchyma and no signs of pancreatic necrosis [29]. Figure 5.1 shows imaging differences between EXPN and pancreatic necrosis. Differentiating acute necrotizing pancreatitis (ANP) from EXPN alone is important as those with the latter have a better prognosis, including a lower risk of developing infected necrosis, need for intervention and mortality as well as a shorter hospital stay [29–31]. Those with EXPN are also less likely to develop diabetes and exocrine insufficiency as there is no loss of pancreatic parenchyma.

Figure 5.1 CT images of extrapancreatic necrosis and parenchymal pancreatic necrosis. (a) Morphological changes and necrosis (arrow) around the pancreas with a normal enhancing pancreas. (b) Hypoenhancement of the head and neck of the pancreas (arrow) consistent with parenchymal pancreatic necrosis with no extrapancreatic necrosis.

Source: courtesy of Elham Afghani.

CT imaging can differentiate an acute peripancreatic fluid collection (AFC) from an acute necrotizing collection (ANC). AFCs are fluid collections associated with interstitial edematous pancreatitis without necrosis, and typically develop within four weeks after onset. CECT of AFC shows a homogeneous collection with a fluid density that is confined to the peripancreatic fascial planes. There is no encapsulating wall which sets it apart from a pseudocyst, which is defined as an encapsulated fluid collection occurring more than four weeks after the onset of interstitial pancreatitis (Figure 5.2). CECT shows a well‐circumscribed homogeneous fluid density with only a liquid component and well‐defined wall [32]. ANC is associated with ANP and, on CECT, is demonstrated by a heterogeneous and non‐liquid density; it is without a definable wall and develops less than 4 weeks after symptom onset. It may be difficult to differentiate AFC from ANC in the first week after onset of symptoms. On the other hand, walled‐off necrosis (WON) is a mature and encapsulated collection of pancreatic or peripancreatic necrosis occurring more than four weeks after onset (Figure 5.3). On CECT, loculations of heterogeneous material is noted in the peripancreatic and/or extrapancreatic space [32]. CECT may also aid in distinguishing infected versus sterile ANC or WON by the presence of gas bubbles within the collection [1].

Figure 5.2 CT image of pancreatic pseudocyst shows a well‐encapsulated collection of fluid (arrow).

Source: courtesy of Elham Afghani.