Mucin stratification in pseudomyxoma peritonei: a pathognomonic ultrasonographic sign

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Pseudomyxoma peritonei (PMP) is a condition characterized by multifocal epithelial peritoneal implants, producing gelatinous ascites made up of copious amounts of mucin, with a primary origin in either the appendix or the ovary. Morbidity results primarily from progressive accumulation of mucin, causing obstruction of the abdominal viscera1. We present a case of PMP showing pathognomonic features on preoperative ultrasound examination, with specific stratification resulting from its viscous gelatinous content as described previously by our group2. A 72-year-old woman presented to the Gynecology Department of Kaplan Medical Center with abdominal pain and ascites. The previous year she had undergone routine abdominal/pelvic ultrasonography because of a family history of ovarian cysts. The examination revealed two hypoechogenic irregular masses in the pelvis (35 and 25 mm in diameter) and a normal left ovary; the right ovary was not visualized. Tumor markers were normal. Follow-up ultrasound examination 5 months later revealed a large amount of free intraperitoneal fluid with multiple septa and a laminated layering pathognomonic of intraperitoneal mucin, with localized echogenic foci which remained immobile when compressed by the ultrasound transducer (Figure 1). The ovaries were not detected during the examination and colonoscopy was normal. An exploratory laparotomy revealed extensive mucinous ascites and a macroscopically normal appendix and ovaries. Cytology revealed mucin and benign epithelial cells. Histology of the appendix revealed a small rupture at the tip with a low-grade mucinous tumor. Histology of the ovaries was normal. Some authors have divided PMP into two diagnostic categories. The first, disseminated peritoneal adenomucinosis, is a relatively indolent disease, comprising borderline malignant epithelial cells derived from a well-differentiated, low-grade mucinous tumor3. This type develops from a ruptured low-grade mucinous appendiceal carcinoma, typically showing hypocellularity and bland cytology, and spreads along peritoneal surfaces without stromal invasion, making it suitable for cytoreductive surgery. The second variant of PMP, peritoneal mucinous carcinomatosis, is more aggressive and infiltrative, comprising poorly differentiated cells that produce large amounts of extracellular mucin4. This latter variant may result from mucinous carcinomas of the gastrointestinal tract, gallbladder, pancreas or ovary, or more rarely, from extraneous sites such as the urachus or the omphalomesenteric duct5. In cases involving the first type of PMP, some have demonstrated synchronous appendiceal and ovarian tumors (90% of cases) whilst others have suggested that the primary lesion is appendiceal and that ovarian disease is metastatic6. There have been a few reports concerning the preoperative ultrasonographic diagnosis of PMP7, 8 which is suspected when ascitic fluid is highly echogenic. The echogenic foci are generally immobile when there is a change in patient position or transducer pressure, differentiating them from those that result from proteinaceous, bloody or fibrinous exudates. The ascitic fluid typically shows echogenic septations with a marked laminated appearance (the ‘onion-skin’ effect), reflecting concentric layering of mucin in the peritoneal cavity, typical of viscous or gelatinous fluid. The septations (borders of mucinous nodules), along with the observable fluid stratification, are relatively pathognomonic of PMP, although both have been described occasionally in other forms of infective ascites and in rare primary peritoneal malignancies9. Dedicated ultrasound scanning is effective in differentiating disorders in patients presenting with ascites and disseminated peritoneal implants. Z. Appelman†, A. P. Zbar*‡, Y. Hazan†, A. Ben-Arie† and B. Caspi† †Department of Obstetrics and Gynecology, Kaplan Medical Center Rehovot (affiliated with Hebrew University, Jerusalem), Rehovot, Israel; ‡Department of Surgery and Transplantation, Chaim Sheba Medical Center (affiliated with Sackler Medical School and Tel Aviv University, Tel Aviv), Ramat Aviv, Israel