Intra-pancreatic Accessory Spleen Mimicking Pancreatic Neuroendocrine Tumor on 68-Ga-Dotatate PET/CT

Imaging of neuroendocrine tumors: A pictorial review of the clinical value of different imaging modalities

Neuroendocrine tumors (NETs) are multifaceted tumors occurring in a variety of organs and often present as metastatic at the time of diagnosis. Accurate staging is the most significant factor in therapy planning, but it remains a challenge. Imaging is established as the cornerstone for disease detection/diagnosis, staging, and follow up. To accurately assess and monitor tumor burden in patients with NETs, various imaging techniques have been developed and optimized. Current recommendations for the imaging of patients with NETs include a combination of both morphologic (or anatomic) and molecular imaging, but a final choice can be puzzling for clinicians. Recognizing that there is no uniform sequence consensus on the "best" imaging test, and the heterogeneity of technologic availability at different centers, we hope to provide a pictorial review of the different imaging techniques and their role and utility in management of patients with NETs, aimed to provide a practical guide for all clinicians.

Impact of PET data driven respiratory motion correction and BSREM reconstruction of 68Ga-DOTATATE PET/CT for differentiating neuroendocrine tumors (NET) and intrapancreatic accessory spleens (IPAS)

To evaluate whether quantitative PET parameters of motion-corrected ⁶⁸Ga-DOTATATE PET/CT can differentiate between intrapancreatic accessory spleens (IPAS) and pancreatic neuroendocrine tumor (pNET). A total of 498 consecutive patients with neuroendocrine tumors (NET) who underwent ⁶⁸Ga-DOTATATE PET/CT between March 2017 and July 2019 were retrospectively analyzed. Subjects with accessory spleens (n = 43, thereof 7 IPAS) and pNET (n = 9) were included, resulting in a total of 45 scans. PET images were reconstructed using ordered-subsets expectation maximization (OSEM) and a fully convergent iterative image reconstruction algorithm with β-values of 1000 (BSREM₁₀₀₀). A data-driven gating (DDG) technique (MOTIONFREE, GE Healthcare) was applied to extract respiratory triggers and use them for PET motion correction within both reconstructions. PET parameters among different samples were compared using non-parametric tests. Receiver operating characteristics (ROC) analyzed the ability of PET parameters to differentiate IPAS and pNETs. SUVmax was able to distinguish pNET from accessory spleens and IPAs in BSREM₁₀₀₀ reconstructions (p < 0.05). This result was more reliable using DDG-based motion correction (p < 0.003) and was achieved in both OSEM and BSREM₁₀₀₀ reconstructions. For differentiating accessory spleens and pNETs with specificity 100%, the ROC analysis yielded an AUC of 0.742 (sensitivity 56%)/0.765 (sensitivity 56%)/0.846 (sensitivity 62%)/0.840 (sensitivity 63%) for SUVmax 36.7/41.9/36.9/41.7 in OSEM/BSREM₁₀₀₀/OSEM + DDG/BSREM₁₀₀₀ + DDG, respectively. BSREM₁₀₀₀ + DDG can accurately differentiate pNET from accessory spleen. Both BSREM₁₀₀₀ and DDG lead to a significant SUV increase compared to OSEM and non-motion-corrected data.

Intrapancreatic accessory spleen false positive to 68Ga-Dotatoc: case report and literature review

Background

Intrapancreatic accessory spleen (IPAS) is an uncommon finding of pancreatic mass. Differential diagnosis with pancreatic tumor, especially with non-functional neuroendocrine tumor (NF-NET), may be very hard and sometimes it entails unnecessary surgery. A combination of CT scan, MRI, and nuclear medicine can confirm the diagnosis of IPAS. 68-Ga-Dotatoc PET/CT is the gold standard in NET diagnosis and it can allow to distinguish between IPAS and NET.

Case presentation

A 69-year-old man was admitted to our hospital for an incidental nodule in the tail of the pancreas with focal uptake of 68-Ga-dotatate at PET/CT. NET was suspected and open distal splenopancreatectomy was performed. Pathologic examination revealed an IPAS.

Conclusion

This is the second IPAS case in which a positive 68Ga-Dotatoc uptake led to a false diagnosis of pancreatic NET. Here is a proposal of a literature review.

Significance of imaging findings in the diagnosis of heterotopic spleen-an intrapancreatic accessory spleen (IPAS): Case report

RATIONALE

Accessory spleen (Heterotopic/Ectopic) or splenunculus has been attributed to the failure of the fusion of splenic primordial buds-derived from dorsal mesentery (mesodermal mesenchymal in origin) during the 5th week of embryonic organogenesis or to an extreme degree of splenic lobulation with pinching off of the spleen tissue. The most common locations for accessory spleens are the hilum of the spleen followed by adjacent to the tail of the pancreas. The patients usually present with no clinical symptoms.

PATIENT CONCERNS

A 49-year-old female undergoing a routine medical examination- Abdominal Ultrasound revealed a pancreatic mass. She was admitted into the hospital for 3 days and was put under observation. There are no specific findings during the physical examination or any related abnormalities in the laboratory investigations.

DIAGNOSIS

Heterotopic spleen-an intrapancreatic accessory spleen (IPAS).

INTERVENTIONS

Noncontrast CT of the abdomen demonstrated a soft tissue mass with a clear boundary in the tail of the pancreas. On contrast examination-the arterial phase, it was markedly enhanced, homogenous congruity similar to that of spleen; on magnetic resonance imaging (MRI)-T2WI with fat suppressed sequence, it demonstrated a regular round clear edged mass in the pancreatic tail. On Diffusion Weighted Imaging (DWI), a mass with a clear boundary was observed within the parenchyma of the pancreatic tail. The mass showed a high signal on noncontrast MRI, while on contrast examination, the mass showed a strengthening signal with homogenous enhancement as that of spleen.

OUTCOMES

Heterotopic spleen presentation is a very rare asymptomatic clinical condition. During the routine medical examination - it presents mostly as a solitary benign round or oval mass with a clear boundary or as an ectopic focus, either in the pancreatic tail or adjacent to the pancreatic appendage, as an incidental finding. On Contrast CT, it shows as a homogeneously enhanced density- a strengthening mass lesion, in the pancreatic tail, similar to that of spleen.

LESSONS

Our case emphasizes the importance of recognizing IPAS radiological characteristics and typical variations in its presentation in an asymptomatic patient that could help the personnel to differentiate it from other mass lesions. Thus, recognizing imaging findings on Plain CT, Contrast CT and MRI plays a key role to form a conclusive diagnosis of an accessory spleen, which has to be clinically associated. So, surgeons should consider IPAS as a differential for which unnecessary resection and an unintended surgical procedure can be avoided.