Diagnostic ultrasound ( PDFDrive )

CHAPTER 18 Organ Transplantation 679
he usefulness of arterial RIs as an indicator of rejection is
controversial. It has been shown that RIs of the arteries supplying
the pancreatic transplant cannot diferentiate allograts with mild
or moderate rejection from normal transplants without rejection. 90
he reason may be that the pancreatic transplant does not contain
a discrete investing capsule, and therefore swelling from transplant
rejection may not necessarily result in increased parenchymal
pressures or elevated vascular resistance. 91 Grossly elevated RIs
greater than 0.8 have been observed in pancreatic allograts with
biopsy-proven acute severe rejection. Although these elevated
RIs may be sensitive, they are not speciic in the detection of
severe pancreatic transplant rejection. 90 Similarly, grat enlargement
and heterogeneity may be seen in acute pancreatitis and
ischemia.
In a small series of patients, CEUS played a useful role in the
surveillance of pancreatic grats and in particular helped in the
earlier diagnosis of rejection. Time-intensity curves in patients
during rejection showed a signiicantly slower ascent and
diminished maximum intensity. Overall, there was a signiicantly
reduced maximum intensity and time to reach peak intensity.
Ater successful treatment of the episode of rejection, these
parameters near normalized to initial values.
Ultimately, image-guided biopsy is the reference standard for
conirming and grading the severity of rejection.
FIG. 18.64 Thrombus Adjacent to Suture Line. Echogenic thrombus
(arrowhead) at suture line (small arrows) of blind-ending ligated artery.
Spectral trace adjacent to thrombus shows to-and-fro waveform (bottom),
whereas spectral trace (top) more distally is normal.
parameters used to evaluate pancreas grat dysfunction have low
sensitivity and speciicity in detection of rejection. In particular,
there is no individual biochemical marker that would permit
acute rejection to be distinguished from vascular thrombosis or
pancreatitis.
Although current advances in immunosuppressives have had
an impact on acute rejection rates, chronic rejection remains
one of the major causes of long-term grat failure.
Hyperacute rejection is rare and occurs in the immediate
postsurgical period, usually as a result of preformed circulating
cytotoxic antibodies in the recipient’s blood. hrombosis and
immediate grat loss occur with this condition.
Acute rejection occurs as a result of an autoimmune vasculitis
and develops 1 week to 3 months ater transplantation. here is
small vessel occlusion, which results in diminished perfusion
and long-term infarction if not treated early. 86 Recurrent episodes
of inadequately treated or unrecognized rejection result in chronic
rejection, with progressive endarteritis of small vessels with acinar
atrophy, and eventually with ibrosis and parenchymal atrophy.
Chronic rejection occurs in 4% to 10% of patients and is seen
as gradual decline in exocrine and then endocrine function.
On gray-scale ultrasound, the allograt may appear hypoechoic
or may contain multiple anechoic regions, and the parenchymal
echotexture may be patchy and heterogeneous 87,88 (Fig. 18.66).
In addition, there may be abnormal grat size, typically enlargement
in acute rejection and atrophy in chronic rejection. Pancreatic
enlargement in acute rejection has a sensitivity of 58% and a
speciicity of 100%. 89
Pancreatitis
Almost all patients develop symptoms of pancreatitis immediately
ater surgery, presumably caused by reperfusion injury and
ischemia. 91 his typically involves the entire grat.
A temporary elevation of serum amylase 48 to 96 hours
posttransplantation is therefore common and usually of no clinical
consequence. here is also a mild transient elevation in amylase.
Focal edema of the donor mesenteric fat attached to the arterial
stump of the SMA should not be misdiagnosed as a focal pancreatitis.
his inding is related to ligation of the donor’s lymphatic
vessels. Other causes of pancreatitis include partial or complete
occlusion of the pancreatic duct, poor perfusion of the allograt,
and, in patients with systemic venous-bladder drainage, reluxrelated
pancreatitis. 87
Long term, grat pancreatitis is seen in up to 35% of transplants.
Underlying predisposing factors include prolonged warm ischemia
time, grat handling, and reperfusion injury. he major diferential
diagnoses to consider include grat rejection and ischemia.
he ultrasound appearance of pancreatitis in the allograt is
similar to that of pancreatitis in the native gland (Fig. 18.67).
Gray-scale indings include a normal-sized or bulky edematous
pancreas, poorly deined margins, increased echogenicity of the
peripancreatic fat secondary to surrounding inlammation,
peripancreatic luid, and thickening of the adjacent gut wall. In
cases of pancreatitis resulting from ductal obstruction, a dilated
pancreatic duct may be observed. 87,91 In nonacute cases of
pancreatitis, pseudocysts adjacent to or distal from the transplant
may be identiied, usually appearing as a well-circumscribed
luid collection with minimal adjacent inlammatory changes.
Needle aspiration of this structure typically demonstrates luid
with high amylase content.
Pancreatitis may be seen in association with vascular sequelae
such as a focal arterial aneurysm or venous thrombosis. Similarly,