British Journal of Radiology (2004) 77, 148-149
© 2004 British Institute of Radiology
doi: 10.1259/bjr/56352047
Intrapancreatic accessory spleen: diagnosis using contrast enhanced ultrasound
T Ota, MD, PhD
1 and
S Ono, MD, PhD
2
Departments of 1 Radiology and 2 Nephrology, Mitsubishi Kyoto Hospital, Katsuragosho-cho, Nishikyo-ku, Kyoto, 6158087 Japan
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Abstract
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Intrapancreatic accessory spleen (IPAS) is a mass that can mimick a neoplastic mass in the pancreas. As it poses no clinical problem no treatment is required. Unfortunately almost all the reported cases of IPAS have been misdiagnosed and unnecessary surgery performed. We performed contrast-enhanced ultrasound (CEUS) in a patient with IPAS for a research purpose, and confirmed that CEUS is useful for diagnosing this entity.
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Case report
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A 31-year-old man with chronic renal failure was diagnosed as having an intrapancreatic accessory spleen (IPAS) by technetium 99m heat damaged red blood cell SPECT when he was 26 years old [1] (Figures 1 and 2
). We performed contrast enhanced ultrasound (CEUS) using a microbubble contrast agent (Levovist; Schering AG, Germany) in order to see whether it can help to obtain the correct diagnosis. Informed consent was obtained from the patient. A bolus of 2.5 g Levovist with a concentration of 300 mg ml-1 was injected intravenously; this injection was followed with a 10 ml normal saline flush. After a delay of 5 min, the delayed hepatosplenic phase of CEUS was imaged using an ultrasound scanner (LOGIQ 500 Pro; GE, USA). A curved array convex probe (model C358) was used. The colour Doppler frequency was 2.5 MHz, and pulse repetition frequency was set to 2.1 KHz. Clear enhancement was shown within the mass as well as the normal spleen (Figure 3) confirming that an IPAS could be diagnosed by CEUS using Levovist.
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Figure 1. Arterial phase contrast enhanced CT. Intrapancreatic accessory spleen (IPAS) (arrow) is located in the tail of the pancreas (P). The structure and density of the mass are quite similar to those of the main spleen (S), but this finding is quite similar to that of pancreatic hypervascular tumours. Reprinted by permission of the Society of Nuclear Medicine from: Ota T, et al. Intrapancreatic accessory spleen diagnosed by technetium-99m heat-damaged red blood cell SPECT. J Nucl Med 1997:38;494–5.
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Figure 2. Technetium-99m-heat damaged red blood cell SPECT, axial plane. Clear accumulation of radionuclide is seen at the site in question (arrow). A liver uptake is also seen (L), probably due to excessive red blood cell damage. S, proper spleen.
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Figure 3. Delayed hepatosplenic phase contrast-enhanced ultrasound (CEUS), left intercostal scan. Grey scale image on the left shows the intrapancreatic accessory spleen (IPAS) (black arrow) which has quite similar echogenicity and internal structure to the main spleen (S). The pancreas (P) shows high echogenicity, likely due to fatty infiltration. Power Doppler image on the right shows clear enhancement of the IPAS (black arrow) as well as the main spleen (S). Blood flow of the splenic vessels is also depicted (white arrows).
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Discussion
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Though rarely noticed radiologically, IPAS is not rare. In an autopsy study of 3000 patients, 61 of 364 (17%) accessory spleens were found in the pancreatic tail [2]. The tail of the pancreas is the second most common site of accessory splenunculi. IPASs are rarely recognised probably because the spatial resolution of CT and MR images has been too low to detect them. As imaging techniques improve, they will be more frequently found. However, diagnosis of this entity is problematic. CT, MRI and ultrasound images of IPAS are quite similar to those of hypervascular pancreatic tumours, such as islet cell tumours and acinar cell carcinoma. Accordingly, almost all the reported cases of IPAS have been misdiagnosed as pancreatic tumours and unnecessary surgery performed [3–5]. Ota et al reported a non-invasive diagnostic method for this entity using SPECT in 1997 [1]. Even following that report, however, IPASs have still been misdiagnosed and unnecessarily resected [4, 5].
Levovist is an ultrasound contrast agent with air microbubbles. In the vascular phase, it produces increased signal intensities in both grey scale and Doppler modes. In the delayed phase, the "hepatosplenic phase", the microbubbles are trapped almost exclusively by the hepatic and splenic parenchyma. The mechanism of this trapping is still debatable [6]. By applying a higher acoustic pressure, the trapped microbubbles are disrupted and produce a non-correlated Doppler signal, which can be visualized as strong transient enhancement. This method is variously known as sonoscintigraphy, loss of correlation, stimulated acoustic emission and transient scattering [7].
Thus, Levovist can distinguish the hepatic and splenic parenchyma from other tissue. Since IPAS consists of normal splenic tissue, the correct diagnosis is readily obtained by CEUS as illustrated by the present case.
IPAS should be included in the differential diagnosis of pancreatic hypervascular masses. Since scintigraphic study and CEUS can both provide the correct diagnosis, they should be considered as a non-invasive means of making the correct diagnosis.
Received for publication August 16, 2002.
Revision received February 25, 2003.
Accepted for publication May 2, 2003.
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References
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- Ota T, Tei M, Yoshioka A, Mizuno M, Watanabe S, Seki M, et al. Intrapancreatic accessory spleen diagnosed by technetium 99m heat-damaged red blood cell SPECT. J Nucl Med 1997;38:494–5.[Abstract/Free Full Text]
- Halpert B, Gyorkey F. Lesions observed in accessory spleens of 311 patients. Am J Clin Pathol 1959;32:165–8.[Medline]
- Takayama T, Shimada K, Inoue K. Intrapancreatic accessory spleen. Lancet 1994;344:957–8.[Medline]
- Lauffer JM, Baer HU, Maurer CA, Wagner M, Zimmermann A, Buechler MW. Intrapancreatic accessory spleen. A rare cause of a pancreatic mass. Int J Pancreatol 1999;25:65–8.[Medline]
- Teshigahara O, Suenaga M, Takeuchi Y, Hayakawa H, Uchida T, Uchimura M, et al. A case of intrapancreatic spleen which was indistinguishable from non-functional islet cell tumor. Jpn J Gastroenterol Surg 2000;33:1821–5.
- Quaia E, Blomley MJK, Patel S, Harvey CJ, Padhani A, Price P, et al. Initial observations on the effect of irradiation on the liver-specific uptake of Levovist. Eur J Radiol 2002;41:192–9.[Medline]
- Calliada F, Campani R, Bottinelli O, Bozzini A, Sommaruga MG. Ultrasound contrast agents: basic principles. Eur J Radiol 1998;27:S157–60.[CrossRef]
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