Intrapancreatic accessory spleen

Clinical History

A 62-year-old man with a history of hypertension, hyperlipidemia, abdominal aortic aneurysm and cerebrovascular accident was investigated for iron deficiency anaemia. Following unremarkable gastroscopy and colonoscopy, he underwent a CT of the abdomen and pelvis.

Imaging Findings

A portal venous phase of the abdomen and pelvis was performed. An incidental enhancing solid lesion in the tail of the pancreas was identified (Figure 1). The lesion measured 2.6 cm in diameter and had a small low attenuation area within it. There was no dilatation of the pancreatic duct and the remainder of the pancreas appeared unremarkable. There was no local lymphadenopathy. No other abnormality was detected.

An MRI of the pancreas was performed to further evaluate the indeterminate lesion.
A pre- and post-contrast MRI scan of the pancreas was performed. On all sequences, the pancreatic lesion showed signal characteristics similar to the adjacent spleen. The lesion showed low signal intensity compared to the pancreas on T1 weighted spin echo sequence (Figure 2) and intermediate-to-low signal intensity on the T2 weighted spin echo sequence (Figure 3). On gadolinium-enhanced images, obtained during arterial phase, the lesion showed intense heterogeneous enhancement (Figure 4).

Discussion

Accessory spleens are congenital splenic nodules, which fail to fuse during embryogenesis. They are histologically identical to the spleen. They are common, identified in up to 16% of cross sectional imaging and up to 30% of autopsies. Their location varies. The pancreatic tail is the second most common location after the splenic hilum [1].
Accessory spleens are asymptomatic and usually do not require treatment. However, the diagnosis of accessory spleens is important for the following reasons:
1. An accessory spleen can mimic primary or secondary pancreatic tumours, which may result in an unnecessary operation.
2. In patients with thrombocytopenic purpura, all functional splenic tissue should be removed as part of their treatment.
3. Rarely, the accessory spleen may undergo spontaneous rupture and cyst formation [2].
CT is the most common modality where intra-pancreatic accessory spleens (IPAS) are first identified. Accessory spleens demonstrate similar attenuation and enhancing characteristics to the adjacent spleen. Generally, IPAS are denser than the surrounding normal pancreatic tissue. Contrarily, most of the hypervascular pancreatic tumours are hyperintense on the arterial phase and hypointense to the adjacent pancreatic tissue on the portal venous phase [2].
On MRI studies accessory spleens share identical signal characteristics with that of the spleen by demonstrating lower signal on T1 weighted images and higher signal compared to pancreatic parenchyma on T2 weighted images. Heterogeneous enhancement of the accessory spleen, which is characteristic of splenic tissue on arterial phase, can be seen on Gadolinium-enhanced MRI [3].
Contrast enhanced ultrasund with microbubbles and Technetium 99m Heat Damaged Red Blood Cell scintigraphy (Technetium-99m HDRBC) have been recently proposed as alternative diagnostic tools [4].
On contrast enhanced ultrasound, the enhancement pattern of accessory spleens is similar to that of the spleen. Prolonged enhancement on delayed hepatosplenic parenchymal phase is a diagnostic ultrasound feature for IPAS [4].
Technetium-99m HDRBC scintigraphy has high specificity for the detection of splenic tissue, with 90% entrapment of the injected HDRBCs within the splenic tissue. Certain volume of functioning splenic tissue is required to be successfully depicted on Technetium-99m HDRBC scintigraphy [2].
In our institution, an IPAS was diagnosed noninvasively. It was first detected on the CT scan and subsequently confirmed on MRI without the need for percutaneous biopsy or operation.
Use of multiple imaging modalities and recognition of the characteristic imaging features are essential for the correct diagnosis of IPAS.

Differential Diagnosis List

Final Diagnosis

Intra-pancreatic accessory spleen

URL:	https://www.eurorad.org/case/13552
DOI:	10.1594/EURORAD/CASE.13552
ISSN:	1563-4086