Ultrasound (US):
Initial study for the assessment of the pancreatic graft.
Disadvantages: operator dependent,
anatomic challenges (bowel gas may cause obscuration of the graft).
Gray-scale US: hypoechoic homogeneous soft-tissue structure (Fig.
1).
Doppler US: demonstrates an optimal parenchymal perfusion and vascular anatomy (Fig.2). Nonspecific Spectral Doppler: normal arterial waveforms show a rapid systolic upstroke and continuous diastolic blood flow.
Venous structures have a monophasic waveform (Fig.
3).
CT:
CT is useful when the ultrasound is difficult to be performed. This technique enables to value all the pancreatic graft anatomy and the recipient small bowel.
Unenhanced CT: is performed in patients with impaired renal function and has limitations in the evaluation of the vasculature and parenchymal enhancement.
Pancreatic graft is a homogeneous soft-tissue structure difficult to distinguish from bowel due to its similar attenuation (Fig.4). Surgical staples of the duodenal stump may help with this inconvenient.
The donor duodenum can be misinterpreted as a fluid collection.
CT with iv contrast: demonstrates parenchymal enhancement and the vascular anatomy of the graft (Fig.5).
MRI:
This technique is particulary helpful when vascular complications are suspected.
Also,
it may aid to complete the assessment of the pancreatic graft when the ultrasound is limited or difficult.
Unenhanced MR: it helps to distinguish the pancreatic graft from adjacent structures.
It is superior to CT without iv contrast.
On T1-weighted images: pancreatic parenchyma homogeneous and hyper intense in relation to the liver.
On T2-weighted images: the signal intensity of the pancreas graft is between that of fluid and muscle.
This is the best sequence to detect abnormalities of the pancreas (Fig.6 and Fig.7).
Postsurgical complications
Important factors that add to frequent and potentially life-threatening postsurgical complications are the complexity of the surgical technique and the immunosuppression state of the patient.
Also,
donor factors may participate as significant risk factors for pancreatitis,
thrombosis,
and graft loss.
Postsurgical complications may be classified in early or late complications,
surgical or nonsurgical complications (usually immunologic) or by an anatomical approach (graft,
vascular and bowel complications).
Graft complications: graft rejection (hyperacute,
acute and/or chronic),
graft pancreatitis (and pancreatitis complications) (Fig.
8).
Vascular complications: graft thrombosis,
graft stenosis,
pseudoaneurysm,
arteriovenous fistula,
hemorrhage (Fig.
9,
10,
11 and 12).
Bowel complications: small bowel obstruction (high risk of internal hernia),
anastomotic exocrine leak and colitis.
Normally,
ultrasound is the initial technique used to evaluate the pancreatic graft complications.
However,
CT is better than ultrasound in the assessment of fluid collections,
abscess formations and/or bowel complications.
Vascular complications may be evaluated with iv contrast CT if ultrasound is limited by technical or anatomical aspects.
Usually,
MRI is reserved to complete ultrasound or CT evaluation or to assess vascular abnormalities.
Considerations:
Graft rejection is the major cause of graft loss and the second most common cause is venous acute graft thrombosis.
Chronic rejection is the first cause after the first 6 months.
Surgical complications are the earliest complications.
They include anastomotic leak,
hemorrhage,
infection and vascular thrombosis.