Frequently associated with loculated ascites of similar attenuation to individual implants
Implants cause mass effect on liver and spleen, producing characteristic “scalloped” appearance
Implants may demonstrate curvilinear calcification
Dominant cystic or solid mass often present in right lower quadrant (in expected location of appendix)
Metastases to ovary are common, so cystic masses in ovaries may not represent primary ovarian neoplasm
Imaging findings of bowel obstruction
• MR: Implants usually low signal on T1WI and high signal on T2WI with possible internal enhancement on T1WI C+
PATHOLOGY
• Mucin-producing neoplasm of appendix causes appendiceal distension and subsequent perforation with diffuse intraperitoneal spread of mucinous implants
CLINICAL ISSUES
• Slowly progressive process with accumulation of implants and development of multiple bowel obstructions
• Primary treatment is cytoreductive surgery and infusion of heated intraperitoneal chemotherapy
• Survival improved with addition of hyperthermic intraperitoneal chemotherapy to cytoreduction, with 5-year survival as high as 77% and 10-year survival of 57%
• Treatment is not curative and is primarily designed to reduce symptoms and prolong survival
(Left) Axial CECT in a patient with a ruptured appendiceal tumor demonstrates large low-density mucinous implants “scalloping” the border of the liver, a characteristic appearance of pseudomyxoma peritonei. At least 1 implant demonstrates peripheral calcification .
(Right) Coronal volume-rendered CECT in the same patient demonstrates the full extent of this patient’s extensive pseudomyxoma, with implants surrounding the liver and stomach, as well as extending into the pelvis.
(Left) Axial CECT in a patient with pseudomyxoma peritonei after a ruptured appendiceal tumor demonstrates extensive cystic implants throughout the upper abdomen, some of which demonstrate subtle curvilinear calcification .
(Right) Coronal volume-rendered CECT better demonstrates the extensive nature of this process, with implants filling nearly the entire abdominal cavity. The patient suffered from periodic bowel obstructions and required several different debulking surgeries.
TERMINOLOGY
Abbreviations
• Pseudomyxoma peritonei (PMP)
Definitions
• Diffuse intraperitoneal accumulation of gelatinous mucinous implants due to rupture of appendiceal mucinous neoplasm
• Terminology is highly debated and variable, and some authors also use the term PMP for mucinous dissemination after rupture of mucin-producing tumors at other sites (i.e., colon, stomach, fallopian tube, ovary, urachus, etc.)
IMAGING
General Features
• Best diagnostic clue
“Scalloping” of liver and spleen by low-attenuation masses
• Location
Diffuse involvement of peritoneum, with implants often quite extensive
Most common locations include greater omentum and bilateral subphrenic spaces (perihepatic/perisplenic)
Implants on serosal surface of bowel are much less common than with peritoneal carcinomatosis
Classically does not metastasize to any distant organs or lymph nodes (other than ovarian implants)
• Size
Implants variable in size, with very small or large implants possible
• Morphology
Gelatinous low-attenuation masses
CT Findings
• Low-attenuation masses (usually < 20 HU) scattered throughout peritoneum with central displacement of bowel loops
Frequently associated with loculated ascites of similar attenuation to individual implants
• Implants cause characteristic mass effect on liver and spleen, producing “scalloped” appearance
• Undersurface of diaphragm may appear thickened and irregular due to frequent subphrenic implants
• Implants may demonstrate curvilinear peripheral calcification
• Dominant cystic or solid mass often present in right lower quadrant (in expected location of appendix)
• Metastases to ovary are common, so cystic masses in 1 or both ovaries may not necessarily represent primary ovarian neoplasm
• Imaging findings of bowel obstruction (dilated small bowel, discrete transition point, and decompressed distal bowel)
MR Findings
• Implants usually low signal on T1WI and high signal on T2WI
Exact signal characteristics can vary depending on amount of mucin in implants
Areas of enhancement within lesions may be visible on T1WI C+ images (more apparent than with CT)
• Characteristic “scalloping” of both liver and spleen by perihepatic and perisplenic implants
• Larger collections of T2 hyperintense loculated ascites often accompany cystic implants
Nuclear Medicine Findings
• PET/CT
FDG uptake often present, but variable: Aggressive histologic subtypes tend to have higher FDG uptake, whereas less aggressive forms have lower uptake
Limited sensitivity for small implants (particularly < 1 cm)
Radiographic Findings
• Radiography
Multiple indirect signs of ascites or peritoneal implants
– Displacement of bowel loops centrally
– Lateral displacement of liver margin and cecum
– Pelvic dog’s ears sign: Lobulated fluid collections in pelvis on either side of urinary bladder
Ultrasonographic Findings
• Mucinous intraperitoneal masses may appear hypoechoic or hyperechoic with no internal color flow vascularity
Conglomerate omental masses may appear echogenic and solid on US (despite appearing cystic on CT)
• Complex multiseptated ascites with characteristic echogenic foci in ascites (likely due to gelatinous fluid)
Imaging Recommendations
• Best imaging tool
CECT
• Protocol advice
Positive oral contrast may helpful to distinguish gelatinous implants from bowel loops
DIFFERENTIAL DIAGNOSIS
Peritoneal Carcinomatosis Without Mucinous Ascites
• Peritoneal metastases most often result from ovarian and GI tract primary tumors
• Discrete tumor implants, when visible on imaging, are more often solid in appearance with frequent associated ascites
Solid tumor implants may become confluent and develop into large conglomerate omental masses (omental caking)
• Very rarely may cause “scalloping” of liver and spleen, but density of implants and known primary malignancy are key to diagnosis
Peritoneal Carcinomatosis With Mucinous Ascites
• Some authors use the term PMP for disseminated spread of any mucin-producing neoplasm (not simply cases with appendiceal primary)
• Implants may appear low density (with “scalloping” of liver and spleen) and be indistinguishable from classic PMP due to appendiceal primary neoplasm
• Primary mucinous ovarian tumors usually present with unilateral dominant pelvic mass, although distinction from PMP often possible only at laparoscopy
• Normal appendix may be clue to diagnosis on CT
•
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Dominant cystic or solid mass often present in right lower quadrant (in expected location of appendix)
Metastases to ovary are common, so cystic masses in ovaries may not represent primary ovarian neoplasm
“scalloping” the border of the liver, a characteristic appearance of pseudomyxoma peritonei. At least 1 implant demonstrates peripheral calcification 
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