Peritoneal Carcinomatosis

Quick Answer

FDG-PET/CT detects peritoneal metastatic disease — from ovarian, colorectal, gastric, appendiceal, and other primaries — and is valuable for staging, restaging, and selecting candidates for cytoreductive surgery ± HIPEC by finding disease that changes operability. Its two important limits are small-volume (miliary) peritoneal deposits below PET resolution and low-grade mucinous disease (e.g. pseudomyxoma peritonei), which is often FDG-poor — both can be underestimated. Physiologic bowel activity and adjacent organ uptake further complicate the crowded abdomen, so PET is read alongside contrast CT/MRI and, where it matters, diagnostic laparoscopy.

What PET sees — and misses

FDG-PET/CT is sensitive for macroscopic, metabolically active peritoneal disease (nodular implants, omental caking, avid ascites-associated nodules) and detects extra-abdominal and nodal disease that alters management. But it is limited for small-volume miliary spread below resolution and for low-grade mucinous carcinomatosis, which is characteristically FDG-poor — so a negative or low-uptake study does not exclude peritoneal disease, especially in mucinous histologies.

High-yield points: omental caking and nodular peritoneal implants are the classic avid findings; mucinous/low-grade disease (pseudomyxoma peritonei, mucinous appendiceal/ovarian tumours) is a recognized false negative; and physiologic bowel FDG (peristalsis, lymphoid tissue, metformin) must be separated from implants — delayed views and CT correlation help.

Where it changes management

For cytoreductive surgery with HIPEC, the peritoneal cancer index (PCI) and resectability drive selection; PET/CT contributes by detecting extraperitoneal or bulky disease that would preclude complete cytoreduction, while laparoscopy remains the reference for the true peritoneal burden because of PET's small-volume limitation. In ovarian cancer recurrence with rising CA-125, FDG-PET frequently localizes peritoneal and nodal recurrence when conventional imaging is equivocal.

Common Pitfalls / Cautions

• A negative FDG-PET does not exclude small-volume or mucinous peritoneal disease.
• Physiologic bowel and urinary activity mimic or obscure implants — correlate with CT/delayed imaging.
• PET complements but does not replace laparoscopy for peritoneal burden before cytoreduction.

Board Pearls

• The classic avid findings are omental caking and nodular peritoneal/serosal implants; PET adds value chiefly by finding extraperitoneal, nodal, or bulky disease that changes operability.
• Two classic false negatives: small-volume miliary spread below PET resolution and low-grade mucinous disease (pseudomyxoma peritonei, mucinous appendiceal/ovarian tumors).
• Common primaries are ovarian (most frequent), colorectal, gastric, and appendiceal.
• FDG-PET is particularly useful in ovarian cancer recurrence with rising CA-125 when conventional imaging is equivocal.
• Diagnostic laparoscopy remains the reference standard for true peritoneal burden (PCI) before cytoreductive surgery/HIPEC.

Differential Diagnosis

• Tuberculous or other infectious peritonitis — FDG-avid peritoneal/omental thickening and ascites that closely mimics carcinomatosis.
• Peritoneal mesothelioma and primary peritoneal carcinoma.
• Post-surgical or reactive inflammation, dialysis-related peritonitis, and endometriosis.
• Physiologic bowel and omental-fat FDG simulating implants.
• Other avid processes such as splenosis, desmoid, or talc/suture granulomas.

Reporting Checklist

• Report distribution (omental caking, implants in subphrenic spaces, paracolic gutters, pouch of Douglas) and any ascites.
• State the small-volume/mucinous limitation — a negative or low-uptake study does not exclude peritoneal disease.
• Identify extraperitoneal, nodal, or bulky disease affecting resectability/complete cytoreduction.
• Separate physiologic bowel/urinary activity using CT correlation and delayed views.
• Correlate with contrast CT/MRI and recommend laparoscopy where peritoneal burden is decision-critical.

Self-Check

Key References

• Reviews of FDG-PET/CT for peritoneal carcinomatosis — sensitivity for macroscopic disease and limits in small-volume and mucinous disease.
• Cytoreductive surgery/HIPEC selection literature (peritoneal cancer index; role of laparoscopy).