Abdominal Mesothelioma

Published on 19/07/2015 by admin

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 20-30% of malignant mesotheliomas arise in peritoneum

• CT: Omental and peritoneal stranding, nodularity, and discrete masses

image Stellate, thickened (pleated) mesentery secondary to encasement and straightening of mesenteric vessels
image Tumor spreads along serosal surfaces and can directly invade adjacent viscera, especially colon and liver
image Can spread across diaphragm into pleural cavity
image Less ascites than peritoneal carcinomatosis
image Calcified pleural plaques may be clue to diagnosis
• MR: Low to intermediate T1WI and intermediate to high T2WI signal intensity of omental and peritoneal masses
• Typically no distant metastatic disease or lymphadenopathy

TOP DIFFERENTIAL DIAGNOSES

• Peritoneal carcinomatosis
• Lymphomatosis
• Pseudomyxoma peritonei
• Tuberculous peritonitis
• Sclerosing mesenteritis

PATHOLOGY

• Relationship with asbestos exposure is less strong than with pleural mesothelioma (requires much higher exposure to asbestos than pleural mesothelioma)

image Asbestos is still strongest risk factor

CLINICAL ISSUES

• Rare tumor (1-2 cases per million) with extremely poor prognosis (most patients die within 1 year)
• M:F > 4:1; usually 6th-7th decade
• Treatment: Cytoreductive surgery and peritonectomy combined with heated intraperitoneal chemotherapy
image
(Left) Axial CECT in an elderly man with abdominal distention shows a calcified pleural asbestos plaque image. The parietal peritoneum under the diaphragm is diffusely thickened image with a discrete mass image.

image
(Right) Axial CECT in the same patient shows an omental mass image with loculated ascites. The abdominal findings are indistinguishable from peritoneal carcinomatosis, but the asbestos plaque is an important clue to the diagnosis of mesothelioma.
image
(Left) Axial CECT in an elderly man with abdominal pain shows marked mass-like omental thickening image and encasement of bowel loops image. Open biopsy confirmed malignant mesothelioma.

image
(Right) Axial NECT in a patient with renal insufficiency shows a lobulated mass image in the omentum abutting the anterior abdominal wall. Surgical biopsy confirmed malignant mesothelioma. Such an isolated mass is an unusual manifestation of the disease, which is usually widespread at the time of diagnosis.

TERMINOLOGY

Abbreviations

•  

Synonyms

• Malignant mesothelioma, peritoneal mesothelioma

Definitions

• Primary malignant neoplasm arising from peritoneum
• “Benign cystic mesothelioma” is misnomer

image More accurately referred to as “peritoneal inclusion cyst”
image Has nothing in common with malignant mesothelioma other than having mesothelial cells in its lining

IMAGING

General Features

• Best diagnostic clue

image Peritoneal masses or omental caking associated with calcified pleural plaques
• Location

image Malignant mesothelioma can arise from pleura, peritoneum, pericardium, tunica vaginalis, or any other serosal membrane in body

– 70% of malignant mesotheliomas arise in pleura
– 20-30% arise in peritoneum
– Very few cases involve both pleura and peritoneum
• Size

image Usually involves peritoneal surfaces diffusely or multifocally
image Focal masses range from few mm to many cm
• Morphology

image 2 primary forms

– Diffuse (desmoplastic): Diffuse disease thickening peritoneal surfaces and enveloping viscera
– Localized (focal): Large tumor mass with scattered satellite peritoneal nodules

Radiographic Findings

• Radiography

image Calcified pleural plaques in 50% of patients with peritoneal mesotheliomas

– Only 20% of pleural mesotheliomas have calcified plaques
– Suggests heavier asbestos exposure in patients with peritoneal mesothelioma

Fluoroscopic Findings

• Separation and fixation of bowel loops
• Spiculation of loops when bowel wall invaded
• Segmental stenoses with circumferential bowel invasion

CT Findings

• Omental and peritoneal stranding, nodularity, and discrete masses

image Stellate, thickened (pleated) mesentery secondary to encasement and straightening of mesenteric vessels
image Spreads along serosal surfaces and can directly invade adjacent viscera, especially colon and liver
image Can spread across diaphragm into pleural cavity
image Calcification in peritoneal masses is very uncommon
• 2 primary forms

image Diffuse (desmoplastic) peritoneal mesothelioma: Diffuse thickening of peritoneal surfaces and omentum with involvement of entire abdomen and multiple discrete masses

– Aggressive form that accounts for majority of cases
image Localized (focal) peritoneal mesothelioma: Solid dominant mass in 1 portion of abdomen without widespread disease or nodularity

– Mass may infiltrate and involve adjacent local organs, but does not spread to distant sites in abdomen
– Lesser degree of ascites
– May have better prognosis, but only represents a minority of cases
• Variable amount of ascites: Massive ascites uncommon

image Amount of ascites in mesothelioma (for a given amount of solid tumor burden) tends to be less than is seen with peritoneal carcinomatosis
• Calcified pleural plaques may be clue to diagnosis
• Does not typically demonstrate distant metastatic disease or lymphadenopathy

MR Findings

• Low to intermediate T1WI signal intensity of peritoneal masses
• Intermediate to high T2WI signal of peritoneal masses

image Fluid-fluid levels secondary to hemorrhage
• Nodules and peritoneal thickening are relatively hypoenhancing on T1WI C+ images

Ultrasonographic Findings

• Hypoechoic, sheet-like peritoneal and omental masses
• Echogenic areas within hypoechoic masses may represent entrapped mesenteric or omental fat

Nuclear Medicine Findings

• Tumor tends to be FDG-avid, although little data regarding use of PET/CT in diagnosis, staging, or surveillance

Imaging Recommendations

• Best imaging tool

image Contrast-enhanced CT
• Protocol advice

image Use water or oral contrast to distend small-bowel loops
image Coronal reformations useful for detecting implants near diaphragm

DIFFERENTIAL DIAGNOSIS

Peritoneal Carcinomatosis

• Most common cause of omental caking and peritoneal implants
• Usually metastatic adenocarcinoma, especially ovarian and other gynecological cancers, stomach, colon, and pancreatic cancers
• Cannot be distinguished from mesothelioma by imaging

image Often associated with liver metastases and lymphadenopathy unlike mesothelioma
image Usually greater degree of ascites than mesothelioma for a given solid tumor burden

Lymphomatosis

• Usually associated with Burkitt lymphoma, high-grade lymphomas, and AIDS-related lymphoma
• May be virtually identical in appearance to carcinomatosis or mesothelioma
• Omental and peritoneal nodules, masses, and caking
• Usually concomitant lymphadenopathy in most cases
• Ascites without loculation

Pseudomyxoma Peritonei

• Disseminated low-density mucinous implants which “scallop” margins of visceral serosal surfaces, especially liver and spleen

image Lower in density than solid implants from mesothelioma and carcinomatosis
image Curvilinear calcifications common in implants
• Most result from appendiceal tumors, but can arise from any mucinous neoplasm including ovary

Tuberculous Peritonitis

• Smooth peritoneal thickening with pronounced enhancement (discrete masses less common)
• High-attenuation ascites (25-45 HU) that is often loculated
• Often associated with low-attenuation lymphadenopathy

Sclerosing Mesenteritis

• Increased attenuation and infiltration of mesentery with small prominent mesenteric nodes
• Can present with solitary discrete calcified mass in end-stage form

Peritoneal Inclusion Cyst

• Walled-off collection of fluid lined by peritoneum
• Occurs almost exclusively in women of reproductive age who have had prior abdominal surgery
• Sometimes (incorrectly) called benign cystic or multicystic mesothelioma

image Unfortunate and potentially confusing misnomer, whose use should be discouraged
image Has nothing in common with malignant mesothelioma

PATHOLOGY

General Features

• Etiology

image Relationship with asbestos exposure is less strong than with pleural mesothelioma

– Asbestos is still strongest risk factor
– Likely requires much higher exposure to asbestos than pleural mesothelioma
– Asbestos may be inhaled or ingested, and likely increases risk for malignancy through chronic irritation of pleura or peritoneum
– 20-40 year latency between exposure and diagnosis
image Other major risk factors include radiation and other carcinogens (especially metal fibers)
image Questionable link with simian virus 40 as cocarcinogen
• Genetics

image Complex karyotypes

– Deletions in 1p, 3p, 6q, 9p, 15q, and 22q in various combinations
• Associated abnormalities

image Asbestos-related pleural and parenchymal lung disease
image Multifocal origin from mesothelial lining of abdomen and pelvis
image 3 histologic types

– Epithelial (54%)
– Sarcomatoid (21%)
– Biphasic (mixed epithelial-sarcomatoid) (25%)

Gross Pathologic & Surgical Features

• Solid tumor masses growing along peritoneal surfaces
• Encasement and invasion of adjacent viscera
• Recurs along surgical and laparoscopy tracts

Microscopic Features

• Variable histologic appearance of tumor cells

image Open biopsy rather than FNA often needed for diagnosis
• Positive immunostaining for calretinin, keratin, vimentin, and thrombomodulin

CLINICAL ISSUES

Presentation

• Most common signs/symptoms

image Pain-predominant type: Patients present with abdominal pain and dominant tumor mass with little ascites
image Ascites-predominant type: Patients present with abdominal distention as a result of ascites and widespread disease (usually without dominant mass)
image Other signs/symptoms

– Weight loss, malaise, cramping, new onset hernia
• Clinical profile

image History of asbestos exposure

Demographics

• Age

image Usually 6th-7th decade but can occur at any age
image Slightly lower mean age compared to pleural mesothelioma
• Gender

image M:F > 4:1
image Higher incidence in women compared to pleural mesothelioma
• Epidemiology

image Rare: 1-2 cases per million
image 200-400 cases diagnosed annually in USA (vs. 2,000-3,000 cases of all types/locations)
image Disease clusters around shipyards, docks, asbestos mines, and factories
image Nonoccupational exposure to asbestos and zeolites common in Turkey

Natural History & Prognosis

• Extremely poor prognosis

image Median survival = 6 months; death usually within 1 year
image Probably slightly worse prognosis than pleural mesothelioma
• Solitary tumors have better prognosis than diffuse intraabdominal disease
• Remains confined to abdominal cavity and invades locally

image Does not disseminate hematogenously to brain, bone, or lung

Treatment

• Options, risks, complications

image Cytoreductive surgery and peritonectomy combined with heated intraoperative intraperitoneal chemotherapy
image Systemic chemotherapy in patients who are not candidates for cytoreduction or intraperitoneal chemotherapy

DIAGNOSTIC CHECKLIST

Consider

• Consider in patients with diffuse peritoneal tumor on CT and stigmata of asbestos exposure
• Peritoneal carcinomatosis is much more common than mesothelioma

Image Interpretation Pearls

• Presence of distant metastases outside abdominal cavity makes malignant mesothelioma unlikely

image
(Left) Axial CECT shows subtle infiltration of the omental fat image and ascites image, findings that may be seen in infectious, inflammatory, or malignant disease.
image
(Right) Axial CECT in the same patient shows a more discrete tumor mass image in the pelvis. At surgery, tumor was found along the entire surface of the peritoneal lining and omentum, and mesothelioma was confirmed.
image
(Left) Axial CECT shows an infiltrative, discrete omental mass image. No other primary malignancy was evident. At laparotomy, there was extensive tumor throughout the omentum and mesentery, diagnosed as primary peritoneal mesothelioma.

image
(Right) Axial CECT of recurrent mesothelioma shows distention of the abdomen due to bowel dilation (partial obstruction) and extensive tumor. The tumor image is somewhat difficult to recognize, as it surrounds the bowel and infiltrates the mesentery.
image
(Left) Axial CECT demonstrates extensive tumor image surrounding the liver and invading the abdominal wall. Other tumor implants image are found elsewhere in the omentum. Notice the relative lack of ascites image despite the large amount of tumor. This was found to represent peritoneal mesothelioma.

image
(Right) Coronal NECT in the same patient demonstrates discrete, pleural-based masses image in the right hemithorax, also found to represent mesothelioma. Pleural and peritoneal mesothelioma in the same patient is quite rare.
image
Axial CECT shows diffuse and focal thickening of the peritoneum and omentum. Bulky peritoneal and omental masses image are also present.

image
Axial CECT in the same patient shows a “pleated” or stiff appearance of the mesentery image, due to diffuse tumor seeding along the leaves of the mesentery. In such cases, it is impossible to distinguish between primary peritoneal mesothelioma and metastases on the abdominal findings alone. This was found to be a case of mesothelioma.
image
Axial CECT shows a multiloculated cystic mass, which proved to be a benign cystic mesothelioma.
image
Axial CECT shows a multiloculated cystic mass filling the pelvis. Surgical excision proved the mass to be a benign cystic mesothelioma.

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de Pangher Manzini, V, et al. Malignant peritoneal mesothelioma: a multicenter study on 81 cases. Ann Oncol. 2009. [Epub ahead of print].

Tanida, S, et al. Combination chemotherapy with cisplatin and gemcitabine in malignant peritoneal mesothelioma. Int J Clin Oncol. 2009; 14(3):266–269.

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