Imaging description

At cross-sectional imaging, intrapancreatic accessory spleens appear as incidental and relatively non-specific solid smooth enhancing masses of variable size in the pancreatic tail (Figures 32.1–32.3). On ultrasound, accessory spleens are usually mildly and homogeneously echogenic with posterior acoustic enhancement, and may demonstrate vascular communication with the splenic vessels [1]. At dynamic CT, accessory spleens remain isointense to the spleen across all phases [2,3]. On MRI, intrapancreatic spleens show low T1 signal intensity, high T2 signal intensity, and isointensity to the spleen on post-gadolinium dynamic sequences [2–4]. The signal on T2-weighted sequences can be slightly brighter than that of the spleen [2–3]. At contrast-enhanced CT or MRI, an intrapancreatic accessory spleen may demonstrate lesser or comparable enhancement relative to the pancreas in the arterial phase and lesser, comparable or higher enhancement on later phases [4], though in my experience an intrapancreatic accessory spleen enhances in parallel with the native spleen and so is usually slightly hypervascular relative to the pancreas.

Importance

An intrapancreatic accessory spleen may mimic more sinister pancreatic pathology including malignancy, resulting in unnecessary surgery unless a benign diagnosis can be confidently established [2, 5].

Typical clinical scenario

An intrapancreatic accessory spleen was found in 61 of 3000 autopsies (2%), as an incidental congenital variant [6]. Given that the diagnosis is rarely made in radiological practice, it is likely most intrapancreatic spleens are occult at crosssectional imaging.