Differential Diagnosis of Pseudomyxoma Peritonei – Evidence‑Based Guideline Summary

Primary Gastrointestinal Sources

Mucinous neoplasms of the colon, stomach, pancreas, and small intestine can produce peritoneal dissemination that mimics pseudomyxoma peritonei, requiring careful pathologic assessment to differentiate them from true appendiceal disease. 1

Breast, colorectal, gastric, pancreatic, and ovarian cancers are the most frequent primary tumors that give rise to peritoneal carcinomatosis resembling pseudomyxoma peritonei. 1
At initial diagnosis, gastric cancer involves the peritoneum in approximately 13 %–27 % of patients, frequently presenting with mucinous or signet‑ring cell histology. [2][3]
Unlike true pseudomyxoma peritonei, secondary carcinomatoses characteristically form solid peritoneal nodules rather than gelatinous mucin collections on imaging and intra‑operative inspection. 1

Tuberculous peritonitis is diagnosed by peritoneal biopsy showing caseating granulomas and acid‑fast bacilli, achieving a diagnostic yield of 84 %–100 %. This condition presents with ascites but lacks the gelatinous mucin typical of pseudomyxoma peritonei. 1

Prior to any therapeutic intervention, serum CA‑125, CEA, and CA19‑9 should be measured; a pattern of elevated CEA and CA19‑9 with normal or only mildly raised CA‑125 favors an appendiceal origin. 1
In pre‑menopausal women, serum α‑fetoprotein and β‑hCG should be obtained to exclude germ‑cell tumors when evaluating mucinous ascites. 1
A thorough history for prior malignancy is essential because breast, colorectal, gastric, pancreatic, and ovarian cancers commonly metastasize to the peritoneum. 1

Abdominal ultrasound demonstrates hyperechoic mucinous ascites with a sensitivity of about 97 % for detecting omental involvement. 1
Contrast‑enhanced CT has limited sensitivity (28 %–51 %) for peritoneal disease despite high specificity (97 %–99 %); therefore, a negative CT does not rule out pseudomyxoma peritonei. 1

Diagnostic laparoscopy with peritoneal cytology and targeted biopsy yields approximately 85 % sensitivity and 100 % specificity for confirming peritoneal disease. 1
Paracentesis with cytologic analysis of three promptly processed samples provides a sensitivity of 96.7 %; however, a negative result does not exclude low‑volume disease. 1

Do not rely exclusively on CT imaging for diagnosis; proceed to laparoscopy in patients who are surgical candidates. 1
Recognize that negative ascitic cytology cannot definitively exclude peritoneal carcinomatosis, especially in early or low‑volume presentations. 1
Routine PET‑CT is not recommended for mucinous peritoneal lesions because these tumors often exhibit low FDG uptake, limiting the modality’s diagnostic utility. 1