A mucinous cystic neoplasm (MCN) is an uncommon tumor characterized by a fluid-filled sac, or cyst, containing a thick, gel-like fluid called mucin. These neoplasms are composed of abnormally growing tissue. MCNs are slow-growing, and many are benign when discovered.
Anatomical Locations and Characteristics
Mucinous cystic neoplasms are most frequently found in the pancreas, with about 93% occurring in the body or tail of the organ. They are less commonly found in the liver or ovaries. Pancreatic MCNs appear as solitary, large cysts ranging from two to 35 centimeters, enclosed by a thick, fibrous wall that may contain calcifications.
A defining feature that distinguishes MCNs from other cysts is a unique tissue layer in the cyst wall known as ovarian-type stroma. This dense layer of cells resembles ovarian tissue. MCNs also do not communicate with the pancreatic duct system. The cysts are often multilocular, meaning they are divided into multiple compartments by thin walls called septations.
Associated Symptoms and Risk Factors
Many MCNs do not cause noticeable symptoms, especially when small, and are often discovered by chance during imaging for unrelated health reasons. When symptoms do occur, they are non-specific and can be attributed to a wide range of other conditions. These may include vague upper abdominal pain, a feeling of fullness, back pain, nausea, or unexplained weight loss.
The primary risk factor for an MCN is being female, as these tumors occur almost exclusively in women, with a female-to-male ratio as high as 20-to-1. The typical age at diagnosis is between 40 and 50 years old. This strong predisposition is linked to the ovarian-type stroma that characterizes the neoplasm.
The Diagnostic Process
Diagnosis begins with imaging studies like a computed tomography (CT) scan or magnetic resonance imaging (MRI). These scans provide detailed pictures of the pancreas, revealing the cyst’s presence, size, and location. They also show characteristics such as thick walls, internal septations, or solid nodules within the growth.
For a more detailed examination, doctors often use a procedure called endoscopic ultrasound (EUS). This involves passing a thin, flexible tube with an ultrasound probe through the mouth to create high-resolution images of the pancreas and cyst. EUS can be combined with fine-needle aspiration (FNA), where a thin needle collects fluid from the cyst. This fluid is then analyzed for tumor markers, such as carcinoembryonic antigen (CEA), and for atypical cells to help confirm the diagnosis.
Malignant Potential and Treatment
MCNs are premalignant lesions, meaning they have the potential to become an invasive cancer like pancreatic adenocarcinoma. The risk of malignancy increases as the cyst grows larger. Features such as thickened walls or solid components visible on imaging also raise suspicion for cancer.
Given this risk, the standard recommendation is complete surgical removal (resection) for patients healthy enough for the operation. The primary goal of surgery is to remove the entire neoplasm before any cancerous cells can develop and spread. The specific procedure depends on the tumor’s location; for MCNs in the body or tail of the pancreas, a distal pancreatectomy is common.
Surgery is recommended because it is difficult to rule out malignancy with biopsies beforehand, as a small area of cancer can exist within a benign-appearing cyst. The prevalence of invasive carcinoma in these neoplasms is reported to be between 6% and 55%, making observation a less favorable option for most individuals.
Post-Treatment Outlook
The long-term outlook following the surgical removal of a non-invasive MCN is very positive. When the entire cyst is successfully resected, the procedure is often considered a cure, with a five-year survival rate of nearly 100%.
After surgery, long-term surveillance with periodic imaging scans may be recommended to monitor for any recurrence. The frequency of this monitoring depends on the surgical pathology report. If the removed MCN was found to contain an invasive carcinoma, the prognosis is more serious. In these cases, five-year survival rates are between 55% and 60%, and more intensive follow-up and potentially additional treatments are required.