Peritoneal disease refers to any condition affecting the peritoneum, the thin membrane that lines the inside of your abdomen and covers most of your abdominal organs. While the term can include infections and inflammatory conditions like tuberculosis, it most commonly refers to cancer that has spread to this membrane, a condition called peritoneal carcinomatosis. This cancer-related form is by far the most clinically significant type, occurring in roughly 20% of people with colorectal cancer and representing an advanced stage of several common cancers.
What the Peritoneum Does
The peritoneum is a single layer of specialized cells sitting on a bed of connective tissue, threaded with blood vessels and lymphatic channels. It does more than just hold your organs in place. Its network of tiny blood vessels regulates the exchange of nutrients, oxygen, and waste products between your bloodstream and the abdominal cavity. The portion covering your intestines and other organs (the visceral peritoneum) drains directly into the liver’s blood supply, which means substances absorbed through it get filtered by the liver before reaching the rest of the body.
This rich blood supply and its direct connection to abdominal organs make the peritoneum vulnerable when cancer cells break free from a nearby tumor. Once cancer reaches this membrane, it can trigger the growth of new, abnormal blood vessels. These new vessels are structurally defective: oversized, irregularly shaped, and leaky. That leakiness allows fluid and proteins to seep into the abdominal cavity, which is why fluid buildup (ascites) is such a hallmark of peritoneal disease.
Types of Peritoneal Disease
Peritoneal disease falls into three broad categories: secondary cancers that have spread from somewhere else, rare primary cancers that start in the peritoneum itself, and non-cancerous inflammatory conditions.
Peritoneal Carcinomatosis (Secondary Cancer)
This is the most common form. Cancer cells from an abdominal organ, most often the ovaries, colon, or stomach, shed onto the peritoneal surface and take root. Occasionally, cancers outside the abdomen can also spread there. Among extraperitoneal cancers that metastasize to the peritoneum, lung cancer accounts for about 59% of cases, followed by breast cancer (13%), urinary tract cancer (14%), kidney cancer (10%), and melanoma (4%). When cancer reaches the peritoneum from a distant site, 87% of those patients already have metastases in other parts of the body as well, reflecting how advanced the disease typically is at that point.
Primary Peritoneal Cancer
This rare cancer originates in the peritoneal lining itself rather than spreading from another organ. Primary peritoneal serous carcinoma occurs almost exclusively in women in their 50s and 60s. It develops from cells in the peritoneum that have the potential to behave like ovarian tissue, which is why it closely resembles ovarian cancer on imaging and under a microscope. The key distinguishing feature is the absence of an ovarian mass.
Inflammatory Peritoneal Disease
Not all peritoneal disease is cancer. Granulomatous peritonitis, an unusual form of inflammation, can be triggered by tuberculosis, fungal infections, sarcoidosis, or even foreign materials like bile or surgical substances. Tuberculous peritonitis is particularly tricky because it mimics peritoneal cancer on imaging, producing thickened peritoneal folds, nodules, and fluid accumulation. A smoother, more uniform thickening with strong contrast enhancement points toward tuberculosis, while irregular nodules suggest cancer.
Common Symptoms
Peritoneal disease, particularly the cancerous forms, tends to cause a cluster of symptoms centered around fluid buildup and pressure on the intestines. Abdominal swelling or bloating is the most common complaint, driven by ascites. This fluid accumulation also causes discomfort, shortness of breath, and sometimes infection.
As disease progresses, cancer deposits can press on or wrap around the intestines, leading to bowel obstruction. This produces severe pain, vomiting, constipation or diarrhea, and difficulty eating. Loss of appetite and unintentional weight loss are common even without obstruction. Because these symptoms overlap with many less serious conditions, peritoneal disease is often not suspected until it’s fairly advanced.
How Peritoneal Disease Is Detected
Contrast-enhanced CT scanning is the first-line imaging tool, with overall sensitivity ranging from 25% to 100% and specificity from 78% to 100% depending on the size and location of tumor deposits. The wide sensitivity range matters: CT reliably catches larger nodules but misses small deposits under 5 millimeters, detecting only 11% to 48% of those. Certain locations are particularly hard to visualize, including the root of the mesentery (where blood vessels feed the intestines), the surface of the small bowel, and the area under the left side of the diaphragm.
MRI with diffusion-weighted imaging performs better for small deposits, with reported sensitivity and specificity of 90% and 95.5%. PET/CT scanning, which highlights metabolically active tissue, has shown pooled sensitivity of 92% in evaluating recurrent ovarian cancer with peritoneal spread. In practice, doctors often use a combination of these tools.
Once peritoneal disease is confirmed, doctors use the Peritoneal Cancer Index to map its extent. This scoring system divides the abdomen into 13 sectors (nine abdominal regions plus four sections of the small bowel) and assigns each a score based on the size of tumor deposits found there. Scores range from 0 to 39, with higher numbers indicating more widespread disease. A PCI below 15 is generally considered lower burden, while 15 or above signals more extensive involvement. PCI is an independent predictor of survival and helps determine whether surgery is a realistic option.
Treatment Approaches
The most aggressive treatment available combines two procedures done together: cytoreductive surgery followed by heated chemotherapy delivered directly into the abdomen.
Cytoreductive surgery aims to remove every visible tumor deposit, which often requires removing portions of multiple organs along with large sections of the peritoneal lining itself. The goal is to leave behind nothing the surgeon can see. Immediately after, heated chemotherapy solution (warmed to 41 to 43 degrees Celsius) is circulated throughout the abdominal cavity for a set period. The heat serves a dual purpose: cancer cells are selectively destroyed at these temperatures, and the warmth increases how much chemotherapy the remaining cancer cells absorb by making their membranes more permeable. Blood flow in tumor tissue stalls in response to the heat, trapping the drug where it’s needed.
For colorectal cancer with peritoneal spread, this combined approach raises the 5-year survival rate from about 6% with standard treatment to as high as 32%, with 1-year survival reaching 72%. The completeness of tumor removal during surgery is the single most important factor determining how well patients do afterward.
Aerosol Chemotherapy
A newer option called pressurized intraperitoneal aerosol chemotherapy (PIPAC) delivers chemotherapy as a fine mist into the abdominal cavity through small laparoscopic incisions. A review of 21 studies covering 932 patients found the procedure to be safe, with intraoperative complications in 11% and postoperative complications in 11.5%. Procedure-related mortality was under 1%. Quality of life scores remained stable or improved during treatment, which is notable for a cancer therapy. PIPAC is currently used primarily for palliative purposes in patients who aren’t candidates for the more extensive cytoreductive surgery, though about 2.3% of ovarian cancer patients treated with PIPAC responded well enough to become eligible for surgery afterward.
Managing Fluid Buildup
For many people with peritoneal disease, managing ascites becomes a central part of daily life. The first-line approach is large-volume paracentesis, where a thin tube is inserted through the abdominal wall to drain accumulated fluid. This provides immediate relief in 78% to 90% of cases, but the effect is temporary, lasting an average of about 10 days before fluid reaccumulates. The overall complication rate for paracentesis is low at 5.5%.
The catch is that repeated drainage means repeated hospital visits. Many patients delay coming in until the fluid buildup becomes severe, which means they spend significant stretches feeling bloated and uncomfortable. To avoid this cycle, a permanently implanted drainage catheter can be placed in the abdomen, allowing fluid to be drained at home. These catheters have a 100% technical success rate for placement, though they carry a higher overall complication rate of about 20%, including catheter blockage (4.4%), infection (4.1%), and fluid leakage around the insertion site (3.5%). Serious complications occur in about 6% of patients. For most people, the tradeoff of being able to drain fluid on their own schedule significantly improves quality of life compared to repeated hospital visits.
Survival and Outlook
Prognosis varies enormously depending on the primary cancer, how extensively the peritoneum is involved, and whether complete surgical removal is achievable. For colorectal cancer with peritoneal spread, the baseline 5-year survival of 6% reflects how serious the diagnosis is, but the jump to 32% with cytoreductive surgery and heated chemotherapy shows that aggressive treatment can meaningfully change the trajectory for selected patients. Men are diagnosed with peritoneal metastases at higher rates than women across most cancer types, and the median age at diagnosis falls between 66 and 70. PCI score, completeness of surgical removal, and the biology of the underlying cancer are the strongest predictors of how long someone will live with this disease.