Intrapancreatic accessory spleen (IPAS) is the most common ectopic splenic tissue variant located in the pancreatic tail. Accessory spleens are found in 10-30% of the general population, and approximately 17% of these are intrapancreatic. This normal anatomical variant is clinically benign and does not require surgical resection. However, it may resemble pancreatic neuroendocrine tumor or other solid pancreatic neoplasms on imaging, potentially leading to unnecessary surgical intervention. Key diagnostic feature: IPAS shows signal/attenuation identical to normal spleen on all CT/MRI sequences and all contrast phases.
Age Range
20-80
Peak Age
-
Gender
Equal
Prevalence
Uncommon
During embryological development, the spleen develops from the dorsal mesenchyme in the left upper quadrant. Splenic tissue fragments can separate from the splenic hilum during normal development and implant in surrounding tissues (especially the pancreatic tail, greater omentum, gastrosplenic ligament). The pancreatic tail is the most common ectopic splenic tissue location due to its anatomical proximity to the splenic hilum. IPAS shows normal splenic histology (white pulp + red pulp) and has identical vascular architecture to the spleen. Therefore, it behaves parallel to the spleen on all imaging sequences and contrast phases — the arterial phase 'zebra pattern' heterogeneous enhancement of the spleen is also seen in IPAS. Tc-99m heat-damaged RBC scintigraphy is the gold standard for confirmation because the reticuloendothelial system sequesters these erythrocytes only in splenic tissue.
The 'follows the spleen' sign is pathognomonic for IPAS. The lesion shows signal/attenuation identical to the spleen on all CT phases (non-contrast, arterial, portal, delayed) and all MRI sequences (T1, T2, DWI, post-contrast). The arterial phase zebra-pattern heterogeneous enhancement of the spleen is also seen in parallel in IPAS. No pancreatic neoplasm mimics the spleen this consistently.
In the arterial phase, IPAS demonstrates enhancement identical to the spleen's characteristic heterogeneous (zebra-pattern) enhancement. This parallel enhancement is the most reliable CT finding for IPAS and plays a key role in differentiation from neuroendocrine tumor.
Report Sentence
A well-defined lesion in the pancreatic tail demonstrating heterogeneous enhancement identical to the spleen in the arterial phase is identified, consistent with intrapancreatic accessory spleen.
In the portal venous phase, IPAS becomes homogeneous and shows attenuation identical to the spleen. In this phase, both the spleen and IPAS show homogeneous enhancement and are observed at slightly different attenuation from the pancreatic parenchyma.
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In the portal venous phase, the lesion becomes homogeneous and shows attenuation identical to the spleen.
On T1-weighted MRI, IPAS shows signal intensity identical to the spleen — typically slightly hypointense to the pancreatic parenchyma, isointense to the spleen. This parallel signal pattern is preserved on all MRI sequences.
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On T1-weighted sequences, the lesion in the pancreatic tail shows signal intensity identical to the spleen.
On T2-weighted MRI, IPAS shows signal identical to the spleen — slightly hyperintense relative to pancreatic parenchyma, isointense to the spleen. On SPIO-enhanced MRI, signal loss is seen in IPAS because SPIO is taken up by the reticuloendothelial system.
Report Sentence
On T2-weighted sequences, the lesion shows signal identical to the spleen, supporting the diagnosis of intrapancreatic accessory spleen.
On DWI, IPAS shows diffusion behavior identical to the spleen. Since the spleen physiologically shows mild diffusion restriction, a similar finding is observed in IPAS. ADC value is the same as the spleen ADC value.
Report Sentence
On DWI, the lesion shows diffusion behavior identical to the spleen, consistent with accessory spleen.
Uptake is observed in IPAS on Tc-99m heat-damaged RBC scintigraphy — the gold standard method confirming the presence of splenic tissue. This test particularly establishes the diagnosis in equivocal CT/MRI cases and prevents unnecessary surgical intervention.
Report Sentence
Uptake is observed in the lesion in the pancreatic tail on Tc-99m heat-damaged RBC scintigraphy, confirming the presence of splenic tissue; the diagnosis of intrapancreatic accessory spleen is established.
Criteria
In pancreatic tail <2 cm, round/oval, homogeneous, identical to spleen on all sequences
Distinct Features
Most common form. Usually incidentally detected. No follow-up or treatment required. May show hypertrophy after splenectomy (compensatory).
Criteria
Cystic component within accessory spleen, cyst wall surrounded by splenic tissue, rare
Distinct Features
Very rare. The presence of cystic component may be confused with pancreatic cystic neoplasm. Peripheral solid rim shows enhancement identical to the spleen — this is a distinguishing clue.
Criteria
2 or more accessory spleens in pancreatic tail, all identical to the spleen
Distinct Features
Rare. Multiple lesions may raise suspicion for metastasis or pNET. Demonstrating parallel behavior of all lesions with the spleen is diagnostic. Tc-99m scintigraphy confirms.
Distinguishing Feature
pNET shows HOMOGENEOUS hypervascular arterial enhancement — IPAS follows the HETEROGENEOUS (zebra-pattern) enhancement of the spleen. In pNET, DWI shows more prominent restriction than the spleen, and portal phase attenuation differs from the spleen. Tc-99m heat-damaged RBC scintigraphy is negative in pNET.
Distinguishing Feature
Hypervascular metastasis (RCC) shows homogeneous arterial enhancement and does not follow the spleen's zebra-pattern. In metastasis, clinical history (known malignancy) and different behavior from the spleen in the portal phase are distinguishing. IPAS is identical to the spleen in all phases.
Distinguishing Feature
SPN typically presents as a large encapsulated mass in young women. SPN has solid-cystic architecture, hemorrhagic areas on T1, and may show peripheral calcification. IPAS is small (<2 cm), homogeneous, and identical to the spleen. SPN does not follow the spleen.
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
no-follow-upIPAS is an entirely benign normal anatomical variant that requires no surgical resection, biopsy, or follow-up. The most important clinical relevance: preventing IPAS from being confused with pancreatic neoplasm (especially pNET) leading to unnecessary surgical intervention (Whipple procedure or distal pancreatectomy). In equivocal cases, Tc-99m heat-damaged RBC scintigraphy provides definitive diagnosis. In patients who have undergone splenectomy, IPAS may show compensatory hypertrophy, and the presence of accessory spleen may be a source of recurrence in hematologic diseases such as ITP.
IPAS is a benign incidental finding that requires no treatment. However, it may be confused with NET or other solid tumors, leading to unnecessary surgery. Demonstrating identical signal to spleen confirms the diagnosis and prevents unnecessary intervention.