Diagnostic ultrasound ( PDFDrive )

CHAPTER 18 Organ Transplantation 677
anastomosis to the recipient iliac or SMV is not an uncommon
inding and is related to mild narrowing at this site.
he most common complications are venous thrombosis and
arterial pseudoaneurysm.
Potential symptoms of grat thrombosis include unexplained
hyperglycemia, grat tenderness, and, in the context of systemicbladder
drainage technique, hematuria and diminished urinary
amylase levels. Potential complications of grat thrombosis include
grat dysfunction and necrosis, pancreatitis, leakage of pancreatic
secretions, and sepsis.
Thrombosis
Grat thrombosis, including both venous and arterial thrombosis,
occurs in 2% to 19% of patients and is the second leading cause
of transplant loss, ater rejection. Pancreatic transplants are more
vulnerable to grat thrombosis than renal transplants because
the rate of blood low in the transplanted pancreas is slower than
that in a transplanted kidney. 80,81 Although the clinical signs and
symptoms of grat thrombosis are nonspeciic, detection of
vascular thrombosis is imperative for both salvaging the transplant
and preventing life-threatening sequelae, such as sepsis and
cardiovascular collapse. Venous thrombosis, which occurs with
an estimated incidence of 5%, is a particular concern because
of the increased risk of hemorrhagic pancreatitis, tissue necrosis,
infection, thrombus propagation, and pulmonary embolism. 81
Grat thrombosis can be categorized as early or late, depending
on the time of diagnosis ater surgery. Early grat thrombosis
occurs within 1 month of transplantation and is secondary to
either microvascular injury during preservation of the grat or
technical error during surgery. Late grat thrombosis occurs 1
month ater transplant surgery and is usually caused by alloimmune
arteritis, in which gradual occlusion of the small blood
vessels eventually culminates in complete proximal vessel occlusion.
80 Other technical factors predisposing to grat thrombosis
include coagulopathies, long preservation time, poor donor
vessels, let-sided grat placement resulting in a deeper anastomosis,
and the use of a venous extension grat. 81
Prompt surgical intervention may be required depending on
the severity of the thrombosis. hrombosis of the grat splenic
artery and vein results in infarction of the grat pancreatic body
and tail. If there is thrombosis of the grat SMA and SMV, it
may result in infarction of the pancreatic head and transplanted
duodenum. In the context of acute thrombosis the grat may
appear enlarged, whereas in more chronic thrombosis the grat
appears difusely atrophic.
Venous thrombosis is far more common than arterial thrombosis
and is either completely or partially occlusive. It can be
localized to the SMV, the splenic vein, or both vessels. A venous
thrombosis may form owing to a phlebitis related to an underlying
pancreatitis. Alternate mechanisms include stasis caused by a
perianastomotic luid collection or a torque on the venous
anastomosis related to a shit in position of the grat resulting
in stretching or twisting. Stasis in a stump of the SMV distal to
the pancreaticoduodenal vessels may be a nidus for venous
thrombosis.
Venous thrombi within the pancreatic grat may remain
localized and not propagate into the portal vein, the iliac vein,
or the IVC (systemic venous drainage) or the SMV (portal venous
drainage). Normal grat function can therefore be maintained. 82
However, the potential for propagation of venous thrombi always
exists, and if not well seen on ultrasound may need to be imaged
dynamically in the venous phase on multiphase computed
tomography (CT) or magnetic resonance imaging (MRI).
Splenic vein thrombosis results in reversal of arterial diastolic
low and absence of splenic venous low on Doppler ultrasound.
Difuse narrowing of the transplanted portal vein can be visualized
with either technique and is typically seen in association with
elevation of venous pressure within the grat.
A combination of systemic anticoagulation and/or thrombolytic
therapy may be necessary to treat complete splenic vein occlusion.
83 Endovascular thrombectomy may also be performed for
partial or occlusive thrombus, provided there is no underlying
pancreatitis or extrinsic vascular compression. 84
Pseudoaneurysms occur at anastomotic sites or elsewhere as
a result of pancreatitis or underlying infections or abscess. hey
can also occur secondary to biopsy or surgical trauma. he
iatrogenic pseudoaneurysms may be seen in association with
arteriovenous istulas. Similar to the stump venous thrombi
described earlier, stasis in low-low surgically created vascular
stumps can occur in peripheral superior mesenteric and splenic
arterial segments and contributes to formation of stump thrombi.
Arterial thrombosis involves the grat SMA, the grat splenic
artery, or the donor Y construct. he pancreas has a smaller
microcirculatory blood low in comparison with other grat types,
and this increases its risk for thrombosis. It is usually mitigated
by the formation of intrapancreatic arterial collaterals, which
means that patency of only one allograt artery (SMA or splenic
artery) is suicient for grat survival and function. hese collaterals
are oten better appreciated on a modality such as CT owing to
the relatively diminutive caliber of the vessels.
hrombosis is least common in the simultaneous pancreaskidney
transplant as compared with the other techniques, as
well as being less likely when the systemic-bladder drainage
technique is used as compared with the portal-enteric drainage
technique. However, kinking of the Y grat is more likely in the
portal enteric technique and is related to the length of the vessel
(the grat is placed higher in the abdomen).
Many of these arterial complications can be managed via
endovascular intervention, including coil embolization and
covered stents. Surgical resection of aneurysms and grating are
usually reserved for patients who have infected grats and
pseudoaneurysms in the setting of abscesses in the transplant
bed.
On ultrasound, occlusive or nonocclusive thrombus may be
visualized within the lumen of the transplanted arteries or veins
(Fig. 18.63). We have also observed several cases of thrombus
occurring at the suture line of blind-ending arteries or veins
(Fig. 18.64). On spectral Doppler, no arterial low is detected in
transplants with occlusive arterial thrombus. In grats with
occlusive venous thrombus, a lack of venous low is detected on
spectral tracing, with high-resistance arterial low showing either
no low in diastole (RI = 1) or reversal of diastolic low. 81 Surgically
ligated arteries containing thrombus may show a cyclic pattern
of low adjacent to the thrombus, which we presume is secondary