1. Case data
Case 1: A 58-year-old female patient was admitted to our hospital on March 4, 2019 with "a 3-day mass in the tail of the pancreas found in physical examination", and the patient's body weight decreased by 5 kg in the past 2 years, and the contrast-enhanced CT examination showed that the arterial phase of the pancreas and the portal vein phase significantly strengthened the nodules, and the CT value of the arterial phase was 198 HU, and neuroendocrine tumor was considered (Fig. 1). Ultrasound gastroscopy showed hypoechoic lesions (0.6 cm×0.8 cm) in the tail of the pancreas, which were blood-rich nodules. The patient had normal tumor markers such as carcinoembryonic antigen, carbohydrate antigen (CA) 19-9 and CA125, no history of impaired glucose tolerance in the past, and normal oral glucose tolerance test results. The patient was diagnosed with pancreatic neuroendocrine tumor (pNET) before surgery, and the patient underwent laparoscopic distal pancreatic body resection under general anesthesia, and the postoperative specimen showed pancreatic accessory spleen (IPAS) tissue with reddish-brown and tough sections (Fig. 2). Postoperative pathology showed that there was no cancer in the parasplenic tissue of the tail of the pancreatic body, and no cancer was found in the incision margin of the pancreatic tissue (Fig. 3).
Note: a, non-contrast period; b, arterial phase; c, venous phase. Nodular anomalous enhancement of 0.8 cm × 0.7 cm in size was seen in the tail of the pancreas, which was unclear in the noncontrast phase, significantly strengthened in the arterial phase, slightly higher in the venous phase, and the degree of enhancement in the arterial phase and venous phase was higher than that of pancreatic tissue (red arrow).
Fig.1 Preoperative CT scan results of case 1
Fig.2 Postoperative specimen from case 1
Fig.3 Postoperative pathological results of case 1 (HE staining, ×100)
Analysis of the causes of misdiagnosis in case 1: (1) CT imaging manifestations were one of the main reasons. The early and portal vein phases of the caudal pancreatic artery showed significant strengthening nodules, regular margins, and no retroperitoneal and peripheral enlarged lymph nodes, which are consistent with those of pNET. Among them, patients with non-functional pNET have hidden symptoms, normal hormone levels, and lack of specific tumor markers, because of their abundant blood supply and internal degenerative necrosis. (2) Although the patient underwent ultrasound gastroscopy, the patient's family refused to undergo puncture and did not perform the operation; (3) Failure to compare the degree of lesion enhancement with the degree of spleen enhancement, and lack of experience in the diagnosis of IPAS.
Case 2: A 60-year-old male patient was admitted to our hospital on September 15, 2022 with "intermittent abdominal pain for more than 10 days". Anamnesis: Splenectomy due to trauma 30 years ago. CT noncontrast + contrast examination showed that the uncinate process of the pancreas was occupied, and the possibility of malignant tumor was considered (Fig. 4); In the tail of the pancreas, a round-like hypodense shadow was observed, with a larger diameter of 3 cm, calcifications at the margins, mild uneven enhancement on enhanced scanning, and solid pseudopapillomas to be ruled out (Fig. 5). Preoperative diagnosis: uncinate process tumor of pancreatic head; cuff mass of pancreas, consider solid pseudopapilloma of the pancreas; After splenectomy. Tumor markers: CA19-9 1 537.07 U/mL, CA125 125.68 U/mL. Intraoperative pancreaticoduodenal combined caudal pancreatic partial resection; Postoperative pathology showed that pancreatic ductal adenocarcinoma of the uncinate process (medium to low differentiation); The caudal parasplenic tissue of the pancreatic body (Fig. 6) showed no cancer at the incision margin of the pancreatic tissue.
Note: a, non-contrast period; b, arterial phase; c, venous phase. The uncinate process of the pancreas is irregularly slightly low-density, 2.7 cm × 3.1 cm in size, weakly enhanced on contrast-enhanced scan, with irregular margins, close to the superior mesenteric vein, and unclear demarcation from the horizontal segment of the duodenum (red arrow).
Fig.4 Preoperative CT scan of the uncinate process of the pancreas in case 2
Note: a, non-contrast period; b, arterial phase; c, venous phase. A slightly low-density circular shadow with a diameter of 3 cm at the tail of the pancreas can be seen in the noncontrast phase, and the arterial and venous phase scans are mildly unevenly enhanced, with calcifications at the margins (red arrows).
Fig.5 Preoperative CT scan of the tail pancreas of case 2
Fig.6 Postoperative pathological results of case 2 (HE staining, ×100)
Analysis of the reasons for the misdiagnosis of case 2: (1) The patient had a history of splenectomy, and the preoperative imaging examination showed that the spleen was absent, subjectively ignoring the possibility of the existence of the accessory spleen, and objectively comparing the imaging characteristics of the accessory spleen tissue with the normal spleen tissue during the imaging examination. (2) The CT characteristics of the patient were a round-like slightly low-density shadow on the tail of the pancreas, and the enhanced scan showed mild uneven enhancement, and calcification was visible at the edges, which may be a solid pancreatic pseudopapilloma or other low-grade malignant tumors. However, calcification of spleen tissue is rare, and the calcification of the pancreatic tail mass in this patient further interferes with clinical judgment. In contrast, the solid part of the solid pseudopapilloma of the pancreas and the cyst wall are often mildly or moderately enhanced, and calcifications can be seen in the lesion, which is often located in the solid part of the lesion, the septum, or its peripheral capsule. The imaging findings of this patient are very similar to those of solid pseudopapilloma of the pancreas, which has a serious impact on the definitive differential diagnosis.
2 Discussion
The accessory spleen is closely related to the embryonic stage of the spleen germ formation, and normally, during the 5th week of embryonic development, the gastric dorsal mesangium from mesenchymal cells differentiates into the spleen, but if the spleen germ is not fully fused, or if a single cell is separated, it develops into an accessory spleen. 80% of the accessory spleen occurs near the hilum of the spleen, 17% occurs in the tail of the pancreas, and can also be seen in the stomach wall, omentum, spleen and colon ligaments, testes, adrenal glands, etc. The incidence of accessory spleen is about 10%, of which the incidence of accessory spleen completely encapsulated in the pancreas is only 2%, i.e., IPAS. IPAS is most commonly misdiagnosed as pNET, and pNET is divided into functional pNET and non-functional pNET, with functional pNET being easily differentiated from IPAS by the patient's hormone levels and other clinical symptoms, while IPAS is most easily misdiagnosed as non-functional pNET. pNET accounts for no more than 2% of all pancreatic tumors, and non-functional pNET only accounts for 15%~41% of all pNETs, most of which are malignant, and radical tumor resection is the most important means to achieve long-term survival of patients, so non-functional pNET with a maximum tumor diameter of > 2 cm must be surgically resected, in addition, except for those with a maximum tumor diameter of < 1 cm or a greater surgical risk, the remaining non-functional pNET ≤ 2 cm should also be surgically resected. However, IPAS does not require surgical intervention, so it is of great clinical significance for a clear differential diagnosis of the two.
There are no obvious specific clinical manifestations of IPAS, and its diagnosis is mainly based on imaging tests. In the noncontrast CT scan, the density of IPAS was similar to that of the spleen, and the degree of enhancement on the enhanced scan was higher than that of the pancreatic tissue, which was consistent with that of the spleen, and the arterial phase showed "spotty" uneven enhancement, and the portal vein phase showed uniform enhancement, but when the diameter of IPAS was small, the arterial phase also showed uniform enhancement. MRI is also of great value in the diagnosis of IPAS, the T1WI signal of IPAS is lower than that of the pancreas, T1WI can show the location, margin, and shape of the mass, and the T2WI signal is similar to that of the spleen, and the MRI enhancement characteristics are similar to CT enhancement. Due to the high ratio of white pulp to red pulp in IPAS, sometimes the signal intensity of IPAS is slightly higher than that of the spleen on T2-weighted images. In addition, diffusion-weighted imaging is also positive in the diagnosis of IPAS, especially in differentiating IPAS from pancreatic solid tumors. RARER THAN IPAS IS IPARAS WITH EPITHELIOID CYST (ECIPAS). The diameter of ECIPAS is usually 2~4 cm; Pathological microscopy usually shows that the cyst is lined with stratified squamous epithelium, and spleen tissue can be seen outside the cyst; The main focus of CT and MRI examination is to identify the spleen tissue around the cyst, and the CT of ECIPAS shows solid partial enhancement, similar to the degree of enhancement of the spleen, and the cystic part of the CT scan is low density and does not enhance after enhancement. A clear preoperative imaging diagnosis and intraoperative frozen pathology sections are essential to avoid overtreatment.
In addition, since the accessory spleen and spleen have the same physiological functions, radionuclide scanning with spleen function visualization is also of great value in differentiating IPAS from pNET. Spleen tissue uses reticuloendothelial cells to intercept and destroy senescent red blood cells, and 99mTc-labeled thermally denatured red blood cells (99mTc-HDRBC) can be concentrated in the spleen and IPAS and visualized on nuclear examination. However, when the spleen wraps around the tail of the pancreas or covers IPAS, the visualization at IPAS is masked by normal spleen tissue, which can easily lead to misdiagnosis. Non-functional pNET can be identified by 68Ga somatostatin analogue (68Ga-SSA) nuclear scan because it contains somatostatin receptors, which is more sensitive than MRI in diagnosing pNETs, but has a higher false-positive rate, and is only diagnostic when the uptake of 68Ga-SSA images is significantly higher than that of the spleen, which may be related to the fact that lymphocytes in spleen tissue also contain somatostatin receptors. Conventional endoscopic ultrasound (EUS) has limited diagnostic value for IPAS, but the ability to diagnose IPAS can be improved by contrasting EUS with Levovist or Sonazid as intravenous contrast agents. Makino et al. found that enhanced EUS with Sonazoid as a contrast agent was sensitive to the abundant vascular and reticuloendothelial cell systems present in IPAS. In addition, there was a difference between IPAS and pNET in terms of EUS qualitative and quantitative elastography, with IPAS presenting a predominantly green image due to the soft texture of the lesions, while pNET presenting a uniform blue image due to the harder texture of the lesions. Further quantification of elastography results as elastic strain rate ratios can improve diagnostic efficiency.
In addition to imaging, EUS-guided fine needle aspiration (EUS-FNA) is a highly specific tool to distinguish IPAS. Tatsas et al. found that CD8 in endothelial cells of the thin layer of the splenic sinus can be detected by immunocytochemical staining, and the diagnosis of accessory spleen can be obtained as long as the endothelial cells of the splenic sinus are obtained. However, due to unfavorable factors such as small masses and deep locations, pathological specimens are often not accurately obtained, and fine needle puncture may lead to adverse events such as pancreatic leakage and hemorrhage. EUS-FNA is still worth considering when imaging is inconclusive and the intrapancreatic mass is large. In recent years, the application of probe-based laser confocal endoscopy (CLE) in the diagnosis of pancreatic mass masses has become a research hotspot, and CLE can identify the microstructure of cells and subcells by acquiring mucosal images magnified by 1 000 times, and perform biopsy diagnosis (optical virtual biopsy). CLE can not only avoid the paratrauma of EUS-FNA, but also improve the diagnostic accuracy of pancreatic masses in combination with EUS-FNA.
To avoid misdiagnosis of accessory spleen, clinicians should first have a full understanding of IPAS, and the possibility of IPAS should be considered for vascular-rich lesions located in the tail of the pancreas, with a diameter of 1~3 cm, clear boundaries and uniform texture. Secondly, in the process of differential diagnosis, it is necessary to comprehensively use imaging examinations such as CT, MRI, PET-CT, etc., especially 99mTc-HDRBC and other highly sensitive examinations. EUS-FNA testing can be used if necessary, but it is necessary to improve the operation skills to avoid adverse events. Patients with confirmed IPAS do not require surgery, and follow-up observation is sufficient. In conclusion, the understanding and identification of IPAS should be further improved in clinical practice to avoid IPAS patients being misdiagnosed and undergoing unnecessary surgery, which will increase the medical burden.
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引证本文 Citation
ZHANG Mengzhe, RAO Jie, ZHANG Zhengle. Report of 2 cases of misdiagnosis of accessory spleen in pancreas[J]. Journal of Clinical Hepatobiliary Diseases, 2024, 40(2): 365-368
Wu Zhendong, Zhou Guoqiang, Xiang Yan, et al . A case report of erythropoietic protoporphyria with liver cirrhosis as the main manifestation[J]. Journal of Clinical Hepatobiliary Diseases, 2024, 40(3): 581-584
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