Peritoneal carcinomatosis


Peritoneal carcinomatosis is intraperitoneal dissemination of any form of cancer that does not originate from the peritoneum itself. PC is most commonly seen in abdominopelvic malignancies. Computed tomography is particularly important for detailed preoperative assessment and evaluation of the radiological Peritoneal Cancer Index. The imaging
findings vary from simple ascites to multifocal discrete nodules and infiltrative peritoneal masses. Various tumours and tumour like conditions can mimic PC. A systematic analysis of CT imaging features is helpful to narrow down the differential diagnosis, staging and effectively guiding the patient management.

Introduction

The peritoneum is a mesothelial lining covering the abdominal cavity and intraperitoneal
organs. Peritoneal cavity contains a small amount of fluid, which circulates under the
influence of negative pressure generated by the diaphragm, gravity and bowel peristalsis. This natural flow pattern
determines the route of spread of disease processes within the peritoneal cavity.
Peritoneal carcinomatosis is defined as intraperitoneal dissemination of any tumor which is not originated from
the peritoneum itself. PC is one of the most common diffuse peritoneal diseases.

Radiographic staging

Peritoneal carcinomatosis without distant metastases represents locoregional disease and has the potential for aggressive
locoregional treatment. Most CT scan findings are however nonspecific as both neoplastic and non-neoplastic
pathologies of the peritoneum present as soft tissue masses, with or without ascites.
Computed Tomography provides direct visualization of primary and secondary peritoneal tumor. The detailed
information about morphology, size and location of peritoneal implants can be obtained. Multidetector Computed
Tomography remains the modality of choice for primary staging, especially in patients with poor
compliance for diagnostic examinations, providing a great deal of information about a large volume of tissue and
permitting assessment of metastatic extraperitoneal disease. Role is limited in detection of early micronodulation
. MDCT for diagnosis of peritoneal metastasis is highly specific,, although sensitivity is low
A detailed preoperative assessment of PC is essential to provide the surgeon information for evaluation of the
radiological Peritoneal Cancer Index. PCI is considered as an important prognostic indicator, also helpful in
guiding therapeutic management. It can also be used in clinical practice during operations.
Several methods of classification have been used to investigate the extent of carcinomatosis. The Peritoneal Cancer
Index of Sugarbaker was chosen by an expert panel as a useful quantitative prognostic tool. It is the most
widely validated and precise quantitative prognostic indicator. It was described by Jacquet and Sugarbaker. It
assesses the distribution and implant size of the cancer throughout the abdomen and the pelvis quantitatively. The
abdomen and pelvis are divided by lines into nine regions. The small bowel is then divided into four regions.
.
LS 0No tumor seen
LS 1Tumor up to 0.5 cm
LS 2Tumor up to 5 cm
LS 3Tumor > 5 cm or confluence

The lesion size of the largest implant is scored as lesion size 0 through 3. LS-0 means no implants
are seen throughout the regions. LS-1 refers to implants that are visible up to 0.5 cm in greatest diameter. LS-2
identifies nodules greater than 0.5 cm and up to 5 cm. LS-3 refers to implants 5 cm or greater in diameter.

Causes

PC is most commonly seen in abdominopelvic malignancies. Ovarian cancer is the commonest cause followed by colorectal carcinoma, pancreatic cancer, stomach cancer and other malignancies including the hepatocellular carcinoma, gallbladder carcinoma, renal cell carcinoma, transitional cell carcinoma, endometrial, cervical cancers and unknown primary. Extra-abdominal conditions such as breast cancer, lung cancer and
malignant melanoma can involve the peritoneal cavity through the haematogenous spread.
Many non-neoplastic and neoplastic conditions may mimic PC, such as tuberculosis, splenosis implant, peritoneal lymphomatosis, pseudomyxoma peritonei and primary peritoneal mesothelioma.

Anatomic considerations

Peritoneum is a thin, translucent serosal membrane of mesodermal origin, covers the surface of the peritoneal cavity,
mesenteries and intraperitoneal viscera.
Peritoneum is divided into visceral and parietal components. The visceral peritoneum covers the intraperitoneal
organs, omenta and mesenteries. The parietal peritoneum lines the abdominal walls; undersurface of the diaphragm;
anterior surface of the retroperitoneal viscera and the pelvis.12The peritoneum subdivided into interconnected
compartments by the peritoneal ligaments and mesenteries which determine the location and routes of spread of
primary and secondary malignancies and infection within the peritoneal cavity. Normally a very small volume of
sterile fluid is present in the peritoneal cavity. This fluid continuously circulates upwards to the subdiaphragmatic
spaces where the subphrenic submesothelial lymphatics provide most of the lymphatic clearance from the peritoneal
cavity. The cephalic movement of peritoneal fluid is augmented by the negative intra-abdominal pressure during
exhalation and bowel peristaltic motion.
Initially, peritoneal fluid accumulates in gravity-dependent spaces, the deep recesses of the pelvis and the lateral
paravesical spaces and then ascends cephalad through the paracolic gutters reaches the subdiaphragmatic spaces. As
the left paracolic gutter is shallow and discontinuous with left subdiaphragmatic space at the phrenicocolic ligament,
most of the fluid takes path through the right paracolic gutter. Completion of the circulatory pathway takes place
caudally by redirection of fluid into the pelvis through the inframesocolic compartment13.
In pathologic conditions the excessive fluid collects in well-defined areas of stasis or arrested flow including the
peritoneal recesses of the pelvis, the right lower
quadrant, the superior aspect of the
sigmoid mesocolon and the right paracolic gutter.
In the cases of primary and secondary peritoneal malignancies, careful evaluation of the peritoneal recesses is
necessary to locate occult disease for proper staging and planning for
debulking procedures.

Pathways of spread

Peritoneum can be involved by direct invasion, lymphatic paths, intraperitoneal seeding or hematogenous spread.
Direct invasion can be contiguous or non-contiguous. Contiguous peritoneal involvement occurs from the involved
organ periphery directly. Non-contiguous direct spread directed by peritoneal reflections, ligaments and lymphatic
channels.
There are two main routes for lymphatic dissemination including the lymphatic system of the greater omentum and
the right side of the subphrenic lymphatic system.
Hematogenous route is the main route for primary tumor with a high grade of malignancy. It includes distant
metastasis from malignant melanoma, carcinoma breast and lung. Peritoneal seeding is predominantly directed by
intraperitoneal circulation of peritoneal fluid.

Common sites of peritoneal implants

Constant circulation of peritoneal fluid allows transcoelomic dissemination of malignant cells. Their deposition and
growth occur at particular sites due to relative stasis of ascitic fluid.1 Undersurface of the diaphragm, omenta, recto-uterine
space, right lower quadrant, left lower quadrant and right paracolic gutter are prone for metastatic implants.

Spectrum of imaging findings in peritoneal carcinomatosis

Peritoneal carcinomatosis is the most common peritoneal neoplastic condition. It can give wide spectrum of imaging
appearances ranging from simple ascites to large peritoneal / omental mass like deposits. Here we present pictorial
review of key CT imaging findings with few of the PC mimics.

Ascites

The presence of ascites is one of the first indicators of peritoneal carcinomatosis. Loculation of ascitic fluid
is further a helpful feature. Ascites is seen in up to 70% of PC cases, although it is non-specific. Subphrenic
lymphatic obstruction and malignancy associated excess fluid production are the main causing factors for ascites. In
some cases, ascites is little or absent.

Omental involvement

Omentum hangs like an apron from the greater curvature of the stomach and the proximal part of the duodenum,
thus it covers the majority of the abdominal organs.
Earlier omental involvement can be manifested by smudge pattern . In later forms, nodular pattern and mixed solid- cystic patterns can be seen.
Subsequently, separation of the colon and the small intestine from the anterior abdominal wall with classic omental
cake appearance takes place.. Ovarian carcinoma is considered to be the most common malignancy
producing omental cake.

Infiltration of the small bowel mesentery

The mesentery is a double layered peritoneal reflection which suspends the jejunum and the ileum from the posterior
abdominal cavity wall. Mesenteric involvement can be manifested by soft-tissue tumor replacement of normal
mesenteric fat, in the form of fat stranding, discrete or confluent nodules, mesenteric mass, and anomalous fixation
of small bowel loops due to stiff and retractile mesentery, produces characteristic pleated and stellate patterns
. Presence of calcified deposits is pathognomonic for mucin producing tumor cell implants, such as mucinous
cystadenocarcinoma ovary
. Small bowel obstruction is one of the most common complications of peritoneal carcinomatosis, can occur secondary to diffusely infiltrating tumor or focal tumor masses.

Serous Peritoneal implants

Micronodules are difficult to access with imaging alone.
peritoneal walls. It is typically found in subdiaphragmatic spaces.
of several centimeters.
Morphological categories of those implants can be either solid, cystic, calcified or mixed
Ascites, peritoneal thickening and enhancement are commonest findings, followed by omental deposits and caking. PC must be considered as the first possibility in the presence of favorable imaging features even in the absence of detectable primary tumor.

PC mimics

Tuberculous peritonitis

Like tuberculosis, Crohn‟s disease also can result in granulomatous peritonitis. Smooth and regular
peritoneal thickening is more in favor of granulomatous peritonitis.

Splenosis implants

The majority of splenosis implants are found after splenic injury by trauma or after splenectomy. Splenic fragments can become implanted anywhere in the abdominal cavity. With imaging splenosis appears as dense well circumscribed lesion with attenuation and enhancement patterns similar to splenic parenchyma.

Peritoneal lymphomatosis

Diffuse peritoneal involvement can be seen in high grade lymphomas, lymphomas complicating AIDS and Burkitt lymphomas. Diffuse peritoneal thickening with multifocal mass and nodules are characteristic imaging features.
Ascites, mesenteric and omental infiltration also can be noted.
Presence of lymph node involvement, encasement of the mesenteric vasculature, producing the „„sandwich‟‟ sign,
homogenously enhancing thickened bowel wall with aneurysmal dilatation of the involved segment and
splenomegaly are associated findings which are helpful in differentiation.

Pseudomyxoma peritonei

Pseudomyxoma peritonei is a rare complication of mucinous tumours of appendiceal or ovarian origin that
results in peritoneal and omental implants. The CT signs of pseudomyxoma peritonei are not specific, combining
peritoneal effusion, peritoneal nodules and invasion of the greater omentum. Gelatinous deposits scalloping over the
hepatic margins, loculated ascites and curvilinear calcification are pathognomonic features. The pressure of
gelatinous material prevents the bowel loops floating towards the anterior abdominal wall, which may be useful sign
in differentiating pseudomyxoma peritonei from ascites.

Malignant peritoneal mesothelioma

Mesothelioma is a rare primary tumour of the connective tissue, originates in the serous membranes of the pleura,
peritoneum or pericardium. Peritoneal involvement is reported in 25% of cases.
Imaging features include ascites, diffuse irregular nodular peritoneal thickening, invasion of omenta and mesentery
with the formation of omental cakes, and mesenteric masses and bowel wall thickening. Coexistence of pleural
abnormalities with positive occupational asbestos exposure history in absence detectable primary tumour goes more
in favor of mesothelioma.
The extent of carcinomatosis represents one of the most important prognostic factors. In patients with PC accurate
preoperative assessment is essential to determine a road map for choosing an optimal type of treatment.

Summary

Various primary and secondary peritoneal conditions present with spectrum of imaging features. Analysis of
peritoneal involvement patterns are helpful in narrowing down the differential diagnosis. Peritoneal carcinomatosis
should be considered if ascites present with irregular peritoneal thickening, nodular omental and peritoneal deposits,
omental caking. Attempt should be made to search for primary site. Tuberculosis can present in dry, wet or fibrotic
forms and can strongly mimic peritoneal carcinomatosis; ascites with smooth or irregular peritoneal thickening are
common findings. Presence of hepatic or splenic miliary microabscesses, splenomegaly, inflammatory thickening of
the terminal ileum and caecum and caseous lymphadenopathy in appropriate clinical scenario support abdominal
tuberculosis. Pseudomyxoma peritonei should be kept in mind if hypo-attenuating deposits are scalloping the
visceral surface of intraperitoneal solid organ margins with calcified peritoneal and/or omental deposits. Presence of
nodular peritoneal / omental / mesenteric deposits in scenario of old splenic injury possibility of splenosis should be
considered. Lymph node involvement, encasement of the mesenteric vasculature, producing the „„sandwich‟‟ sign
are helpful in differentiation of peritoneal lymphomatosis. Knowledge of the peritoneal anatomy together with an
understanding of the mechanisms behind malignant tumoural seeding of the peritoneal cavity aids in the
interpretation of often complex imaging appearances in peritoneal carcinomatosis. A systematic approach is
important for accurate assessment.