Pseudomyxoma peritonei (PMP) is characterized by the widespread accumulation of a gelatinous, mucus-like material, known as mucin, within the abdominal and pelvic cavities. Informally called “jelly belly,” PMP is considered a low-grade malignancy. It is a slow-growing disease that does not typically spread through the bloodstream or lymphatic system like most common cancers. Instead, PMP fills the peritoneal space, eventually compressing internal organs and interfering with their function, which is often fatal if left untreated.
The Primary Site of Origin
PMP originates from a mucin-producing tumor, most frequently an appendiceal mucinous neoplasm arising in the appendix. This primary tumor produces an excessive amount of mucin, causing the appendix to distend. Eventually, the appendix ruptures due to internal pressure, releasing the gelatinous substance and mucin-producing tumor cells into the abdominal cavity.
Once released, these tumor cells and the mucin spread across the peritoneum, the membrane lining the abdominal wall and covering the organs. The spread follows the natural flow of peritoneal fluid. Tumor cells tend to implant themselves in areas of fluid reabsorption, such as the omentum and the underside of the diaphragm. Although the appendix is the source in the majority of cases, PMP can rarely originate from other sites, including the colon, bladder, or ovaries.
Recognizing the Signs
Because PMP develops slowly, patients often do not experience noticeable symptoms in the early stages. When symptoms appear, they are typically vague, leading to frequent misdiagnosis or delayed diagnosis. The most common sign is a gradual, unexplained increase in abdominal girth or waist size, caused by the accumulation of mucinous fluid.
Patients may also experience persistent abdominal or pelvic discomfort, general bloating, and a feeling of fullness after eating small amounts of food. Changes in bowel habits, such as constipation or diarrhea, can occur as the growing volume of mucin puts pressure on the intestines. Increased intra-abdominal pressure may also lead to the development of a hernia. For women, PMP sometimes presents as an enlarged ovary, which may be mistakenly identified as the primary source of the disease.
Diagnosis and Classification
Diagnosing PMP requires a combination of imaging studies and tissue analysis, as non-specific symptoms do not immediately suggest the condition. Initial investigation involves cross-sectional imaging, such as a Computed Tomography (CT) scan or Magnetic Resonance Imaging (MRI). These scans visualize the characteristic presence of mucinous fluid and tumor implants on the peritoneal surfaces. For example, a CT scan may show a distinctive “scalloping effect,” where mucin accumulation indents the surface of the liver or spleen.
A definitive diagnosis relies on obtaining a biopsy of the tumor tissue or mucinous fluid, often through diagnostic laparoscopy. A pathologist examines the tissue to confirm the presence of mucin and classify the cellular characteristics of the tumor. PMP classification is important because it dictates the patient’s prognosis and treatment plan.
PMP is classified based on the aggressiveness of the tumor cells. Low-grade disease is characterized by abundant mucin with epithelial cells showing minimal signs of atypia. High-grade disease contains more abundant tumor cells that exhibit features of carcinoma, including greater cellular atypia and mitotic activity. The five-year survival rate for patients with low-grade disease is significantly better than for those with high-grade disease, highlighting the importance of this distinction.
Specialized Treatment Strategies
The standard treatment strategy for PMP is a two-part procedure requiring a dedicated team of surgical oncologists. The first component is Cytoreductive Surgery (CRS), an extensive operation aimed at removing all visible tumor deposits and accumulated mucin from the abdominal cavity. This procedure is complex, often lasting many hours, as the surgeon must meticulously strip the peritoneum and remove all affected tissues.
This aggressive surgery frequently involves the removal of organs or parts of organs where tumor implants have attached, known as visceral resections. Common resections include:
- The appendix
- Parts of the colon
- The omentum (a fatty apron over the intestines)
- The spleen
- The ovaries and uterus (in women)
The goal of CRS is to achieve a complete cytoreduction, meaning no visible tumor nodules larger than 2.5 millimeters remain. This outcome is a strong predictor of long-term survival.
Immediately following tumor removal, the second part of the treatment, Hyperthermic Intraperitoneal Chemotherapy (HIPEC), is performed in the operating room. HIPEC involves circulating a heated chemotherapy solution directly throughout the abdominal cavity for 60 to 90 minutes. The chemotherapy agents are heated to a temperature around 41 to 42 degrees Celsius.
The purpose of heating the chemotherapy is twofold: the elevated temperature helps destroy cancer cells, and it increases the depth of penetration of the drugs into the tissue. This direct application allows a high concentration of the drug to reach microscopic cancer cells or small residual tumor implants not visible during CRS.
Following the combined CRS and HIPEC procedure, patients require careful and long-term follow-up care and surveillance. Monitoring often includes regular CT or MRI scans and blood tests to check tumor marker levels for signs of recurrence. While the CRS/HIPEC approach is effective for low-grade PMP, systemic chemotherapy delivered intravenously may be considered for patients with high-grade disease or those whose tumor cannot be fully removed. This specialized treatment is typically only offered at medical centers with expertise in peritoneal surface malignancies.