NORMAL POSTOPERATIVE FINDINGS
During the first postoperative period no imaging studies should be performed unless a complication is clinically suspected.
During this period CT may show a series of findings that should be considered "normal" as physiological consequence of the surgery.
Among these,
the most common are pneumobilia,
perivascular cuffing,
fluid collections,
adenopathy,
acute anastomotic edema,
peripancreatic fat stranding,
stents and free air.
All these findings are intended to resolve over time [1,
3,
5,
8].
Pneumobilia
The presence of air in the biliary tract is an extremely common finding (67 - 80% of cases).
Its presence can help to identify the biliary anastomosis (Fig 4) [2,
8].
Perivascular Cuffing
Perivascular cuffing appears as a thickening of the mesenteric fat which can occur within the surgical bed and surrounding the celiac axis and its branches and the superior mesenteric artery.
It can potentially be extremely focal and mass-like in appearance (Fig 5).
This cuffing is due to an inflammatory reaction and can be seen in up to 60% of the Patients.
In Patients with negative surgical margins this finding should not be mistaken for a local recurrence [1,
3,
5,
8].
Fluid Collections
Thin-walled or poorly delineated transient fluid collections are often seen (28.5%) during the early postoperative period (first 14 days),
usually in the surgical bed and near the anastomoses (Fig 6) [1,
3,
8].
Adenopathy
It is common to identify prominent lymph nodes in the central mesentery and surrounding the surgical bed,
sometimes larger than 1 cm (Fig 7).
These lymph nodes are almost always inflammatory and should regress at follow-up imaging [5].
Acute anastomotic edema
Thickening at the pancreatic anastomosis is a common finding and it is due to acute postoperative edema.
This condition could lead to a dilatation of the main pancreatic duct (Fig 8).
For the same reasons,
mild intrahepatic biliary dilatation could be seen.
These findings should not be misinterpreted as anastomotic strictures and will typically improve with time [1,
5].
COMPLICATIONS
CT is the modality of choice after pancreatic surgery to demonstrate early and late surgical complications such as pancreatic fistula,
hemorrhage,
acute pancreatitis of the remnant,
abscess,
aneurysms,
anastomotic bilio-digestive stenosis and local recurrence.
Other imaging modalities are used to answer to specific questions,
such as the evaluation of gastro-intestinal function (barium studies) or the study of biliary and pancreatic ducts (MRI) [3].
Postoperative pancreatic fistula (POPF)
POPF is the most common major complication after partial pancreatic resection and is associated with increased length of hospital stay,
costs and mortality.
POPF has been defined by the ISGPS as "the presence of drainage fluid on the third postoperative day or later,
with an amylase content greater than three times the upper normal serum value" [9].
It represents the failure of healing/sealing of the pancreatic anastomosis or a leak of pancreatic juices from the raw resection margin [6,
10].
The incidence reported in the literature is between 10% and 30 %,
and the major risk factors are a small main pancreatic duct (diameter <3 mm),
a soft parenchymal texture and intra-operative bleeding [5,
6].
Imaging studies,
especially CT,
can confirm the clinical suspicion of POPF.
The CT features suggesting the presence of POPF are: fluid collections next to the pancreaticojejunostomy or the raw resection margin and in the pancreatic bed,
air bubbles in a peripancreatic collection,
disruption of pancreaticojejunostomy or pancreaticogastrostomy (Fig 9) [5,
10].
If CT fails to demonstrate the typical findings of a POPF,
conventional fistulography could demonstrate with certainty the dehiscence of the anastomosis.
In this examination contrast media is injected under fluoroscopy control through a drainage.
The passage of contrast material into the jejunum or the stomach is diagnostic (Fig 10) [6,
10].
Delayed gastric emptying (DGE)
The second most important complication is DGE,
which has a prevalence between 20% and 50%.
It is defined as the impossibility of resuming oral feeding after the first postoperative week or the prolonged use of a nasogastric aspiration tube.
The diagnosis is not based on imaging,
but the presence of a severely distended stomach at CT is highly suggestive (Fig 11) [3,
7].
Postoperative bleeding
Bleeding occurs in 2 - 16% of cases after pancreatic resection and can be roughly divided into two groups based on its time course: early (≤ 24 hours) or late (> 24 hours).
The location is either intraluminal or more often extraluminal [7].
In most of cases hemorrhage results from active bleeding at the gastroduodenal artery (GDA) stump and could be related to inadequate surgical ligation or vascular erosion (usually secondary to POPF).
Mortality is high (38%).
CT is the imaging technique of choice because it can identify sites of active extravasation or pseudoaneurysm formation (Fig 12) [5].
Hepatic infarction
Ischemic complications are rare with a prevalence of 1% and are essentially arterial in origin [7].
These are due to trauma during dissection of the hepatic artery or celiac trunk resulting in infarction of the left lobe. A selective infarction of the right lobe happens due to the inadvertent sacrifice of a replaced right hepatic artery.
In most of cases ischemia is actually related to a pre-existing stenosis of the superior mesenteric artery or the celiac trunk [5].
CT reveals a hypo-dense and hypo-vascular area with air bubbles in case of superinfection (Fig 13).
The same findings could be seen in MRI.
Postoperative pancreatitis
The diagnosis of post-operative pancreatitis may be challenging,
especially in mild pancreatitis,
because fat stranding and inflammatory changes in the surgical bed and surrounding the pancreatic remnant are normal findings.
Moreover the serum levels of amylase and lipase are unreliable.
In severe cases CT can highlight collections,
both necrotic or purely fluid,
and huge peripancreatic inflammatory changes (Fig 14) [5,
7].
Portal vein and superior mesenteric vein thrombosis (SMV)
In the past decades the complexity of procedures and incidence of surgical venous reconstructions have markedly increased.
As a consequence,
there is a significant incidence (almost 17%) of venous thrombosis (SMV or portal vein) after pancreatic resection.
The development of venous thrombosis can be disastrous,
causing intestinal ischemia,
ascites,
hepatic ischemia,
and death.
CT is the best imaging tool due to its high spatial resolution and the possibility to obtain multiplanar reconstructions,
especially in the coronal plane (Fig 15) [5,
7].
Abscesses
Abscesses can arise secondary to a superinfection of an acute postoperative fluid collection,
more often associated to a leakage from one of the anastomoses that have been created (Fig 16).
The incidence,
regardless of the underlying cause,
ranges up to 6% [5,
7,
8].
Leaks from the biliary-enteric anastomosis
Bile leaks are relatively rare (3,7% of cases) and usually related to technical failure.
The presence of bile in a drainage is highly suspicious for a biliary fistula.
CT can demonstrate the presence of a fluid collection near the bilio-enteric anastomosis.
A differential diagnosis with a POPF can be difficult because the two anastomoses are very close.
Fistulography can demonstrate the passage of contrast medium into the jejunal loop through the biliary anastomosis (Fig 17).
MR can reveal the presence of a fluid collection and,
if a hepatobiliary contrast agent is used,
in the late phases a leak of contrast can be seen [3,
5,
7].
Anastomotic stricture
It is the most common delayed complication after PD,
and can occur both at the pancreaticojejunostomy (4,6% at 5 years) and at the hepaticojejunostomy (8,2% at 5 years).
Ultrasound,
CT and MRI can show a dilatation of the biliary tree or the main pancreatic duct. MRI with MRCP sequences is the best imaging technique to evaluate the ductal systems and the caliber of the anastomoses (Fig 18).
Any change in duct size requires a careful evaluation of the anastomotic site for any signs of local tumor recurrence resulting in ductal obstruction [3,
5,
7].
Tumor recurrence
The identification of tumor recurrence in the surgical bed or as distant metastatic disease is essential to define the prognosis of the patient and to plan any further therapies. It can be identified using ultrasound,
CT or MR.
Local recurrence can appear as an infiltrating mass in the surgical bed or surrounding the mesenteric vessels (Fig 19).
The anastomoses can be involved with subsequent dilatation of the biliary tree or of the main pancreatic duct.
CT is the most accurate (93,5%) in identifying relapse of disease.
MR has,
actually,
very similar potential compared to CT and has a higher sensitivity and specificity in the diagnosis of hepatic metastases [5].