Pseudomyxoma Peritonei

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 Frequently associated with loculated ascites of similar attenuation to individual implants

image Implants cause mass effect on liver and spleen, producing characteristic “scalloped” appearance
image Implants may demonstrate curvilinear calcification
image Dominant cystic or solid mass often present in right lower quadrant (in expected location of appendix)
image Metastases to ovary are common, so cystic masses in ovaries may not represent primary ovarian neoplasm
image 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
image
(Left) Axial CECT in a patient with a ruptured appendiceal tumor demonstrates large low-density mucinous implants image “scalloping” the border of the liver, a characteristic appearance of pseudomyxoma peritonei. At least 1 implant demonstrates peripheral calcification image.

image
(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.
image
(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 image.

image
(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

image “Scalloping” of liver and spleen by low-attenuation masses
• Location

image Diffuse involvement of peritoneum, with implants often quite extensive
image Most common locations include greater omentum and bilateral subphrenic spaces (perihepatic/perisplenic)
image Implants on serosal surface of bowel are much less common than with peritoneal carcinomatosis
image Classically does not metastasize to any distant organs or lymph nodes (other than ovarian implants)
• Size

image Implants variable in size, with very small or large implants possible
• Morphology

image Gelatinous low-attenuation masses

CT Findings

• Low-attenuation masses (usually < 20 HU) scattered throughout peritoneum with central displacement of bowel loops

image 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

image Exact signal characteristics can vary depending on amount of mucin in implants
image 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

image FDG uptake often present, but variable: Aggressive histologic subtypes tend to have higher FDG uptake, whereas less aggressive forms have lower uptake
image Limited sensitivity for small implants (particularly < 1 cm)

Radiographic Findings

• Radiography

image 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

image 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

image CECT
• Protocol advice

image 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

image 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
• Appendectomy frequently performed during surgery for presumed metastatic ovarian cancer or mucinous carcinomatosis without known primary in order to exclude PMP

Tuberculosis Peritonitis

• Variable amounts of free or loculated complex ascites with infiltration of omentum ± discrete masses
• Often associated with other evidence of tuberculosis in abdomen, including low-attenuation mesenteric nodes and thickening of cecum and terminal ileum

Bacterial Peritonitis

• Ascites ± loculated fluid collections or discrete abscess with smooth thickening and hyperenhancement of peritoneum
• Ascites may be slightly higher in attenuation than simple ascites and may demonstrate internal complexity (septations, debris)

Abdominal Mesothelioma

• Rare primary malignant neoplasm arising from peritoneum
• Omental and peritoneal stranding, nodularity, and discrete masses on CT with variable ascites (usually less ascites than carcinomatosis)
• Tumor appears solid, rather than cystic implants seen more frequently with PMP

PATHOLOGY

General Features

• Etiology

image Mucin-producing neoplasm of appendix causes appendiceal distension and subsequent perforation with diffuse intraperitoneal spread of mucinous implants
image Strict definition of PMP encompasses only mucinous dissemination from primary appendiceal tumor
image Much confusion about terminology, as many authors use the term PMP to refer to intraperitoneal spread of any mucin-producing adenocarcinoma of appendix, ovary, fallopian tube, GI tract, lung, etc.
• Genetics

image No known genetic association

Staging, Grading, & Classification

• Ronnet classification (1995)

image Type I: Adenomucinosis (also known as disseminated peritoneal adenomucinosis or DPAM)

– Cytologically bland adenomatous cells and mucin without frank adenocarcinoma and better prognosis

image Some consider it as not truly benign, but representing well-differentiated adenocarcinoma
– Believed to be due to rupture of adenoma or mucocele
image Type II: Mucinous adenocarcinoma (also known as peritoneal mucinous carcinomatosis or PMCA)

– Frank adenocarcinoma and mucin with worse prognosis
image Type III: Intermediate

– Mixture of types I and II with combination of adenoma and adenocarcinoma cells with mucin
• World Health Organization (WHO) and American Joint Committee on Cancer (AJCC) divided PMP into 2 types: Low-grade mucinous adenocarcinoma and high-grade mucinous adenocarcinoma

Gross Pathologic & Surgical Features

• Gelatinous intraperitoneal masses
• 44% have synchronous tumors of ovary (likely metastatic)
• Diffuse peritoneal involvement common

image Most common sites of involvement

– Right subphrenic space
– Liver surface
– Left subphrenic space
– Spleen surface
– Morison pouch
– Left paracolic gutter
– Pouch of Douglas or rectovesical space
• Primary appendiceal tumor often impossible to identify

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

image Most commonly abdominal distension and development of new-onset inguinal hernia
image Abdominal pain, weight loss
image Patients with more extensive disease may present with symptoms of bowel obstruction
image Not uncommonly an unexpected finding encountered at surgery performed for other suspected diagnoses (i.e., appendicitis)
• Clinical profile

image Elevated CEA and CA19-9 often present

Demographics

• Age

image Adults with mean age of 53 years
• Gender

image F > M (2-3x more frequent in females)
• Ethnicity

image No known association
• Epidemiology

image Rare, with incidence of 1 per million

Natural History & Prognosis

• Slowly progressive process with progressive accumulation of implants and loculated ascites and development of multiple bowel obstructions
• Survival has improved with addition of hyperthermic intraperitoneal chemotherapy to standard cytoreduction, with 5-year survival as high as 77% and 10-year survival of 57%
• In general, all patients eventually die from this disease

Treatment

• Primary treatment is cytoreductive surgery (Sugarbaker procedure) with debulking of intraperitoneal implants and infusion of heated intraperitoneal therapy

image Complex surgery with significant morbidity (11-21% require reoperation due to complications) and mortality (0-14%)
• Some groups have reported using systemic chemotherapy, radiotherapy, or intraperitoneal isotope therapy, although little supportive evidence
• Multiple repeat surgeries often required due to progressive disease, and each surgery becomes more difficult due to adhesions and fibrosis
• Treatment is not curative and is primarily designed to reduce symptoms and prolong survival

DIAGNOSTIC CHECKLIST

Consider

• Consider pseudomyxoma peritonei in patients with low-density tumor implants throughout abdomen with “scalloping” of liver and spleen
• Presence of dominant unilateral ovarian mass in conjunction with mucinous implants in peritoneum makes metastatic ovarian cancer more likely than PMP

Image Interpretation Pearls

•  

image
(Left) Coronal CECT demonstrates the earliest stage of pseudomyxoma peritonei, with a dominant mucinous implant image in the right lower quadrant found to be the result of a ruptured appendiceal mucocele. No other implants were present elsewhere.
image
(Right) Sagittal ultrasound in a patient with pseudomyxoma peritonei demonstrates a perihepatic implant image. Despite appearing cystic on CECT, implants on US can appear solid or echogenic.
image
(Left) Axial CECT demonstrates characteristic “scalloping” of the liver by small perihepatic implants image. The implants are low density, but slightly higher in attenuation (∼ 20 HU) than simple fluid.

image
(Right) Coronal CECT in the same patient demonstrates extensive low-density implants occupying a substantial portion of the abdomen. Not surprisingly, the patient suffered from frequent bouts of bowel obstruction.
image
(Left) Axial CECT in a patient with pseudomyxoma peritonei shows extensive low-attenuation gelatinous masses involving the lesser sac and surrounding the stomach, with more nodular soft tissue infiltration laterally image.

image
(Right) Axial CECT in a patient with cystic peritoneal implants from pseudomyxoma peritonei shows calcified perisplenic implants image. Calcifications, often curvilinear and peripheral, are not uncommonly seen with implants in pseudomyxoma.
image
Axial CECT shows pseudomyxoma peritonei with “scalloping” of the liver contour image.

image
Axial CECT shows cystic peritoneal implants from pseudomyxoma peritonei. Note the large cystic mass indenting the anterior aspect of the liver image.
image
Axial ultrasound in a patient with pseudomyxoma peritonei demonstrates cystic splenic and perisplenic implants image.
image
Axial CECT demonstrates ligamentous involvement in a patient with pseudomyxoma peritonei. Note the low-density implants involving the gastrohepatic image and falciform image ligaments.
image
Axial CECT demonstrates “scalloping” of the liver contour image and falciform ligament implant image in a patient with pseudomyxoma peritonei.
image
Axial CECT in a patient with a disseminated high-grade appendiceal neoplasm demonstrates low-density mucinous tumor implants image along the periphery of the pelvic cavity.
image
Axial CECT demonstrates “scalloping” of the border of the liver and spleen by low-density mucinous implants in a patient with pseudomyxoma peritonei.
image
Axial CECT in a 70-year-old woman with mucinous tumors of the ovaries and peritoneal cavity from an unknown primary malignancy reveals “cystic” tumor implants throughout the peritoneal cavity, some of which have focal calcifications image.
image
Axial CECT in the same patient again demonstrates the multiple cystic lesions throughout the peritoneal cavity. Note the presence of an ileostomy image, which was performed to alleviate the bowel obstruction.
image
Axial CECT in a patient with prior surgery for appendiceal carcinoma, now with progressive abdominal distension and a partial bowel obstruction, shows massive, loculated, complex ascites. Note the “scalloped” surface of the liver and spleen, and the large loculation within the lesser sac image, often indicative of malignant or infected ascites.
image
Axial CECT in the same patient reveals an ostomy image, reflecting the obstruction due to bowel and mesentery compression by the peritoneal tumor.
image
Axial CECT in a 57-year-old man with mucinous colon cancer shows complex ascites with loculation, mass effect, and lesser sac involvement. Note the “scalloped” surface of the liver due to multiple cystic tumor implants on the peritoneal surface.
image
Axial CECT in a 76-year-old man with appendiceal carcinoma demonstrates the classic “scalloped” appearance of the liver surface due to the peritoneal metastases. The lesser sac is distended with the malignant ascites image.
image
Axial CECT in a 61-year-old man with recent resection of an appendiceal carcinoma, now presenting with abdominal distension, shows a classic “scalloped” surface of the liver and spleen due to loculated mucinous collections of malignant ascites image.
image
Axial CECT in the same patient reveals the presence of an ileostomy image, which was required because the loculated mucinous peritoneal metastases resulted in compression, distortion, and partial obstruction of the bowel.
image
Axial CECT in a 62-year-old man with a history of appendiceal carcinoma, now presenting with progressive abdominal distension and partial bowel obstruction, demonstrates massive, loculated ascites. Note the scalloped surface of the liver and spleen image due to peritoneal tumor implants.
image
Axial CECT in the same patient reveals that the cystic or gelatinous metastases are also evident as omental masses image.

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