AJR 2004; 183:405-407
© American Roentgen Ray Society
Imaging of an Accessory Spleen Presenting as a Slow-Growing Mass in the Transplanted Pancreas
Kousei Ishigami1,
Bradley Hammett1,
Masao Obuchi1,
Daniel Katz2,
Stephen Rayhill2,
Ahmed Fathala1 and
Monzer Abu-Yousef1
1 Department of Radiology, University of Iowa Carver College of Medicine, 200
Hawkins Dr., 3885 JPP, Iowa City, IA 52242-1077.
2 Department of Surgery, University of Iowa Carver College of Medicine, Iowa
City, IA 52242-1077.
Received October 13, 2003;
accepted after revision October 23, 2003.
Address correspondence to K. Ishigami
(Kousei-Ishigami{at}uiowa.edu).
Introduction
Tumor development in a transplanted pancreas is fatal for the graft and the
recipient [1,
2]. Distinguishing a benign
condition in the pancreatic graft from malignant tumors is important because
it significantly changes patient care. We encountered a case of
intrapancreatic accessory spleen presenting as a slow-growing mass in the
transplanted pancreas. To the best of our knowledge, ours is the first case
report describing this entity occurring in a transplanted pancreas. Radiologic
findings and differential diagnoses will be discussed.
Case Report
A 45-year-old woman was referred to our institution for further evaluation
of a mass in the tail of the transplanted pancreas, which was incidentally
found on CT at an outside institution. She underwent combined kidney and
pancreas transplantations 5 years previously and total splenectomy 20 years
before for idiopathic thrombocytopenic purpura. She was asymptomatic and
healthy.
Contrast-enhanced CT showed a 3.5 x 3.5 cm well-defined round mass in
the tail of the transplanted pancreas, which was almost isodense to the
transplanted pancreas. Otherwise, no intraperitoneal nodules or
lymphadenopathy was seen. An unenhanced CT scan obtained 4 years before was
available, which showed a small soft-tissue-density nodule in the transplanted
pancreas, measuring approximately 1.2 cm in diameter
(Fig. 1A).
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Fig. 1A. —45-year-old woman with accessory spleen in transplanted
pancreas. Unenhanced CT scan obtained 4 years earlier shows
soft-tissue-density nodule (arrow) in tail of transplanted
pancreas.
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MRI showed the mass to be of low signal intensity on the T1-weighted image
and of high signal intensity on the T2-weighted image
(Fig. 1B). A
gadolinium-enhanced T1-weighted image showed homogeneous enhancement that was
of low intensity relative to the transplanted pancreas
(Fig. 1C). Coronal image showed
a beak sign at the interface between the mass and pancreatic graft
(Fig. 1C).
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Fig. 1B. —45-year-old woman with accessory spleen in transplanted
pancreas. Axial T2-weighted fast spin-echo image with fat saturation shows
high-intensity round mass, which shows apparent interval increase in size.
Signal intensity of mass appears similar to that of spleen. Note flow void in
mass.
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Fig. 1C. —45-year-old woman with accessory spleen in transplanted
pancreas. Gadolinium-enhanced coronal T1-weighted fast spoiled gradient-echo
image with fat saturation reveals mass to be of relatively low intensity
compared with pancreatic graft. Note beak sign, which suggests that mass
arises from tail of transplanted pancreas.
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Sonography revealed a round homogeneously hypoechoic mass arising from the
tail of the transplanted pancreas. Color Doppler sonography showed blood
vessels in the mass, suggestive of a vascular hilum
(Fig. 1D). The diagnosis of an
intrapancreatic accessory spleen was suspected.
The slow interval growth of this mass could be explained by compensatory
hypertrophy after splenectomy. We obtained a technetium-99m-labeled
heat-damaged RBC SPECT scan, which clearly showed the uptake of the
radionuclide in the mass of the transplanted pancreas
(Fig. 1E). The patient is being
followed up without invasive diagnostic methods with the diagnosis of an
accessory spleen in the transplanted pancreas.
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Fig. 1E. —45-year-old woman with accessory spleen in transplanted
pancreas. Coronal technetium-99m-labeled heat-damaged RBC SPECT scan shows
accumulation of radionuclide (arrow) at mass in tail of transplanted
pancreas.
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Discussion
An accessory spleen is a common entity, occurring in approximately 10% of
the population. The most common site of an accessory spleen is the splenic
hilum, with the pancreatic tail being the second most common site. In a
postmortem study, 61 (17%) of 364 accessory spleens were found in the pancreas
[3]. An intrapancreatic
accessory spleen has been reported presenting as a mass in the tail of the
pancreas
[4–7].
A differential diagnosis of intrapancreatic accessory spleen includes
hypervascular pancreatic tumors such as neuroendocrine tumors (islet cell
tumor and carcinoid) and metastatic renal cell carcinomas. Additionally, in
our patient, posttransplantation lymphoproliferative disorder would be
included because of the patient's previous history of transplantations
[2].
The spleen has relatively low signal intensity on T1-weighted images and
high signal intensity on T2-weighted images compared with the liver. These
characteristics are shared with pancreatic tumors
[4]. The key for diagnosing
intrapancreatic accessory spleen is that MRI signal intensities of the mass
are similar to those of spleen on multiple pulse sequences
[4,
5]. In our patient, MRI signal
intensities were similar to those of typical spleen characteristics, and the
beak sign suggested that the origin of the mass was the tail of the
transplanted pancreas.
The interval growth of the accessory spleen was thought to be the result of
compensatory hypertrophy after splenectomy. On the basis of a retrospective
review of the previous CT scan, the accessory spleen showed slow but apparent
interval growth. If the patient had a native spleen, the accessory spleen in
the pancreatic graft might not have presented as a mass lesion. Venous phase
CT may fail to reveal a small intrapancreatic accessory spleen because it is
almost isodense to the pancreas. However, sonography is often used for
follow-up studies after transplantation. Even a small intrapancreatic
accessory spleen may be incidentally found on high-resolution sonography as a
hypoechoic round mass.
Radionuclide splenic scanning using 99mTc-labeled sulfur colloid
or 99mTc-labeled heat-damaged RBC is highly specific for
differentiating spleen from other tissues
[7]. If the nuclear medicine
study confirms the splenic tissue, invasive diagnostic methods can be
avoided.
Splenosis is another form of ectopic splenic tissue, which is due to
splenic trauma or autotransplantation of splenic tissue after splenectomy.
Splenosis usually presents as multiple intraperitoneal masses. On the other
hand, accessory spleens are few or solitary. Bertolotto et al.
[8] reported gray-scale and
Doppler sonographic features of the accessory spleen and splenosis. They
described autotransplanted splenic grafts or splenosis as oval with lobulated
margins, and both color and power Doppler sonography showed multiple
peripheral feeding vessels. In contrast, accessory spleens were round with
smooth margins, and color Doppler and power Doppler sonography showed a
vascular hilum [8]. In our
patient, Doppler sonography showed a vascular hilum in the mass, which was
consistent with an accessory spleen rather than splenosis.
In summary, we present a case of intrapancreatic accessory spleen in the
tail of the transplanted pancreas. To exclude malignant tumors, one should be
aware that this entity can be seen even in the transplanted pancreas. Not only
radiologic findings but also typical location may be helpful to reach the
diagnosis of an accessory spleen. If the diagnosis of an accessory spleen is
suspected, obtaining a radionuclide splenic scan is warranted to avoid
invasive diagnostic methods.
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Introduction
Case Report
