History:
Asymptomatic,51 years lady found to have a heteroechoic lesion noted in the head of the pancreas during a master health checkup. The patient was referred to Kauvery hospital for further investigation.
CT ABDOMEN WITH CONTRAST: Large well-defined hypodense lesion in the head and neck of the pancreas with central calcification and mild homogeneous enhancement in the delayed phase, with the lesion abutting the distal most superior mescentric vein, splenic vein and portal vein confluence and encasing the distal most SMV by 90 degrees near the confluence – Possibly serous cystadenoma.
The superior mesentric artery is well away from the lesion.
MRI WITH CONTRAST & MRCP:
Well-defined lesion in the head and neck of the pancreas, appears hypointense on T1W, hyperintense on T2W images with central hypointensity (Corresponding to the central calcification in CT). Few tiny T2W hyperintense cystic areas were noted in the periphery of the lesion. It shows mild homogeneous contrast enhancement in the delayed phase. In DWI, the lesion shows restricted diffusion.
The lesion is abutting the distal most splenic vein, superior mesenteric vein and portal vein confluence with 90% encasement of the superior mesenteric vein at its confluence in the portal vein. The superior mesentric artery is well away from the lesion. The lesion is causing anterior displacement of the MPD. No dilatation of the MPD was noted. No obvious communication was seen.
Main pancreatic duct is pushed away from the lesion.
DIAGNOSIS
Serous Cystadenoma of the pancreas
DISCUSSION:
The prevalence of pancreatic cystic lesions are reported to be between 2.6% to 19.6%. Pancreatic serous cystic neoplasms account for approximately 16%. CT remains the first-line imaging modality of choice due to more widespread availability. Most serous cystic neoplasms are benign and represent pancreatic serous cystadenomas. Serous cystadenoma is a benign neoplasm composed of glycogen-rich epithelial cells that form innumerable small thin-walled cysts containing serous fluid. EUS and fluid aspiration may be helpful in differentiating serous cystadenoma from other pancreatic cystic lesions. Mucinous from nonmucinous lesions are discriminated by the presence of mucin and carcinoembryonic antigen > 192 ng/mL in the fluid aspirate. Fluid aspirate with amylase < 250 U/L excludes pancreatic pseudocysts.
Approximately 60% of cases of SCA arise from the pancreatic body and tail and 40% arise from the pancreatic head and uncinate process. The high predilection for middle-aged and older women are usually discovered incidentally. Most of the patients are asymptomatic. Patients may present with non-specific symptoms such as abdominal pain, abdominal mass, and rarely jaundice.
Classically, SCA has been described as multilobulated multiloculated cystic masses with central stellate scars and calcifications. However, serous cystadenomas have a wide spectrum of CT appearance, ranging from unilocular cystic masses to hypervascular solid masses, which may mimic other benign and malignant pancreatic masses.
Serous cystadenomas can be morphologically classified as polycystic, honeycomb, oligocystic, and solid patterns.
| Typical features | Atypical aggressive features |
|---|---|
| Central scar ± calcifications | Pancreatic parenchymal atrophy |
| Lobulated external contour | Dilatation of pancreatic duct and/or common bile duct |
| No communication with pancreatic duct | Invasion of adjacent structures |
Patterns of pancreatic serous cystadenoma
Microcystic pattern
The microcystic pattern / polycystic pattern, found in 70% of SCA cases consists of a collection of>6 cysts that range from a few millimeters up to 2 cm in size. Fine external lobulations are a common and characteristic feature. A fibrous central scar with or without a stellate pattern of calcification is highly specific for serous cystadenoma. Serous cystadenomas do not usually communicate with the pancreatic duct.
Honeycomb pattern
The honeycomb pattern is seen in∼20% of cases. It consists of numerous tiny cysts that mimic a honeycomb or a sponge. These tiny cysts may be poorly depicted as individual cysts on CT. These serous cystadenomas appear as soft tissue or mixed attenuation masses depending on the size of the cysts and the amount of enhancing fibrous tissue
Oligocystic pattern
The oligocystic pattern is also known as the macrocystic pattern with a prevalence of less than 10% of cases. It is composed of fewer but larger (> 2 cm) cysts and lacks the central stellate scar. It is difficult to differentiate the oligocystic variant from mucinous cystic neoplasms or side-branch IPMN. The presence of external lobulations favors serous cystadenoma over mucinous cystic neoplasms and IPMNs. Dilatation of the pancreatic duct is an unusual feature seen in rare cases.
Solid pattern
Rare cases of a solid variant of serous cystadenoma have been reported. The stroma shows avid contrast enhancement and accounts for the solid hypervascular appearance on CT. Serous cystadenomas also demonstrate intratumoral hemorrhage and also show a high-density solid appearance. This pattern is easily misdiagnosed as a neuroendocrine tumor of the pancreas/ other solid pancreatic neoplasms.
Cystic pancreatic lesions mimicking pancreatic serous cystadenomas
SCA exhibit a wide spectrum of heterogeneous pattern on CT.
| Cystic pancreatic mass | Key distinguishing features |
|---|---|
| Pseudocyst | Smooth external contour Peripancreatic stranding Clinical history of pancreatitis |
| Mucinous cystic neoplasm | Smooth external contour Relatively thick enhancing wall Peripheral calcifications Thick internal septations and nodularity suggestive of malignancy |
| IPMN | Pleomorphic and tubular external contour Communication with main pancreatic duct or side-branch Thick internal septations and nodularity suggestive of malignancy |
| Cystic neuroendocrine tumor | Presence of hypervascular halo Presence of liver metastases Clinical history of endocrinopathy (rare in cystic neuroendocrine) 25% association with MEN syndrome |
| Von Hippel-Lindau disease | Multiple pancreatic lesions, including cysts, serous cystadenomas, and neuroendocrine tumors Other stigmata: renal cell carcinoma, pheochromocytoma, CNS and retinal hemangioblastomas |
| Lymphoepithelial cyst | Protrude into peripancreatic soft tissues |
Solid pancreatic masses that mimic serous cystadenomas
| Solid pancreatic mass | Key distinguishing features |
|---|---|
| Adenocarcinoma | Ill-defined margins Vascular invasion Pancreatic duct dilatation and parenchymal atrophy Common bile duct dilatation Liver metastases and lymphadenopathy |
| Neuroendocrine tumor | Clinical history of endocrinopathy Presence of liver metastases |
| Solid pseudopapillary neoplasm | Young women Cystic solid mass with thick tumor capsule Intratumoral hemorrhage |
| Metastasis (i.e. renal cell carcinoma) | History of renal cell carcinoma Presence of suspicious renal mass |
Management
Management of serous cystadenomas depends on the age of the patient and comorbidities, tumor size and location, presence or absence of symptoms, local practice patterns, and surgeon preferences. Surgical resection is the treatment of choice for symptomatic patients and patients with tumors > 4 cm in size regardless of symptoms. Follow-up imaging every 2 years is recommended for SCA lesions with sizes between 2 and 3 cm. The estimated doubling time is 12 years for SCA. Doubling of size in less than 12 years may be taken up for resection regardless of the initial reported size.
All cases of serous cystadenomas not having typical CT features. According to American College of Radiology Incidental Committee guidelines, for asymptomatic patients with pancreatic cystic lesions, the recommendation is a single follow-up in 1 year for lesions smaller than 2 cm, with no further follow-up if the patient still does not manifest any clinical symptoms.
Dr Shabna Jasmin K
Radiologist