Peritoneum, mesenetry and retroperitoneal tumors 2

BY
DR. HAYTHAM FAYED
ASSISTANT PROFESSOR OF SURGICAL ONCOLOGY
ALEXANDRIA FACULTY OF MEDICINE

Surgical Anatomy of the Peritoneum

NEOPLASMS OF THE PERITONEUM
Primary peritoneal tumors Classification
 Defined as tumors with primary
manifestation in the peritoneum in the
absence of a visceral site of origin.
 They arise from mesothelial cells,
submesothelial mesenchymal cells, and
uncommitted stem cells
Mesothelial tumors
 Peritoneal malignant mesothelioma
 Well-differentiated papillary mesothelioma
 Multicystic mesothelioma
 Adenomatoid tumor
Epithelial tumors
 Primary peritoneal serous carcinoma
 Primary peritoneal serous borderline tumor
Smooth muscle tumor
 Leiomyomatosis peritonealis disseminata
Tumors of uncertain origin
 Desmoplastic small round cell tumor,Solitary fibrous
tumor

Malignant mesothelioma
 Malignant mesothelioma is a highly lethal malignancy of the serosal
membranes of the pleura, peritoneum, pericardium, or tunica vaginalis
testes.
 The peritoneum is the second most frequent site of origin of
mesothelioma, following the pleura.
 The pathogenesis of all forms of mesothelioma is strongly associated with
industrial pollutants, of which asbestos is the principal carcinogen
associated with the disease.

EPIDEMIOLOGY AND RISK FACTORS —
 In the US, malignant peritoneal mesothelioma (MPM) accounts for about 10 to
15 percent of all cases of mesothelioma, and there are about 400 new cases
diagnosed annually.
 Mesothelioma rates are rising worldwide, largely a reflection of occupational
asbestos exposure.
 The median age at presentation is 53, younger than that of the average patient
with pleural mesothelioma.

Risk factors
 Asbestos
 Radiation therapy

CLINICAL PRESENTATION
 There are no signs or symptoms that are specific for malignant peritoneal
mesothelioma (MPM).
 Although most cases are symptomatic, a few are diagnosed incidentally,
after inquiry into an unrelated process, such as infertility, or recognized
during a routine physical examination

 The majority of cases of MPM present with diffuse peritoneal involvement
and are variably referred to as diffuse peritoneal mesothelioma, malignant
peritoneal mesothelioma or just peritoneal mesothelioma.
 However, a minority of cases has localized disease, and they have a
different presentation and natural history

 Diffuse MPM is highly aggressive, with a few exceptions (such as the well-
differentiated papillary mesotheliomas that occur in women
 In contrast, patients with a localized MPM usually have a good prognosis
following complete surgical excision

 Clinical manifestations of diffuse MPM are related to ascites or tumor
progression within the abdominal cavity.
 Common complaints include abdominal distention and/or increasing
abdominal girth, abdominal pain or discomfort, nausea, anorexia, and weight
loss.
 Gastrointestinal complications such as bowel obstruction are usually a
manifestation of advanced disease.

 Pain is the second most common initial symptom and is present at
diagnosis in 27 to 58 percent of patients.
 In most cases, the pain is diffuse and nonspecific, although a small
minority present with an acute abdomen secondary to perforation or
obstruction.

 The less common localized form of MPM presents as a focal,
circumscribed mass that may invade locally and extend into adjacent
organs, but typically does not spread diffusely throughout the peritoneal
cavity.
 Patients may complain of localized abdominal pain or have a palpable
abdominal or pelvic mass

 Morbidity and mortality from MPM are almost invariably due to disease
progression within the peritoneal cavity. However, MPM may also extend
into the pleural cavity during the latter stages of disease progression,
causing a pleural effusion.
 Uncommonly, MPM metastasizes to the abdominal and pelvic lymph
nodes. Lymph node metastases are found in approximately 20 to 28
percent of patients undergoing cytoreductive surgery for diffuse MPM.
 Distant metastases are very uncommon

Paraneoplastic phenomena — :
 Fever
 Thrombocytosis
 Malignancy-related thrombosis
 Hypoglycemia
 Rarely, Coombs-positive hemolytic anemia

Malignant Peritoneal Mesothelioma
CT features:

Differential diagnosis —
Based on imaging findings, the differential diagnosis for a typical diffuse
MPM includes:
 peritoneal carcinomatosis,
 serous peritoneal carcinoma,
 ovarian carcinoma in women,
 lymphomatosis, and
 tuberculous peritonitis.

Differential diagnosis —
 Liver metastases and lymphadenopathy are more common with peritoneal
carcinomatosis from gastrointestinal tract primary neoplasms than they
are with MPM.
 The finding of diffuse adenopathy with a lack of omental involvement
should raise suspicion for lymphomatosis.

DIAGNOSIS AND HISTOLOGY —
The diagnosis of peritoneal mesothelioma should be considered in any
individual with evidence of a diffuse malignant process in the abdomen on
initial clinical and radiographic evaluation, and it can usually be established
cytologically or by biopsy.
CT-guided core needle biopsy or laparoscopic biopsy may both provide
sufficient material to make a tissue diagnosis.

STAGING
 A novel tumor-nodal-metastases or “TNM” staging system has been
proposed that takes into account the extent of disease in the peritoneum (T
stage), the presence of intra-abdominal lymph node metastases (N), and the
absence or presence of extra-abdominal disease (M).
T stage is calculated based on the peritoneal cancer index (PCI, a measure of
the volume and extent of tumor deposits as follows:
 T1 – PCI 1-10
 T2 – PCI 11-20
 T3 – PCI 21-30
 T4 – PCI 31-39

STAGING
 A novel tumor-nodal-metastases or “TNM” staging system has been proposed
that takes into account the extent of disease in the peritoneum (T stage), the
presence of intra-abdominal lymph node metastases (N), and the absence or
presence of extra-abdominal disease (M).
Stage groupings, which were associated with a progressive decrease in survival,
were as follows:
 Stage I – T1 N0 M0; five-year survival 87 percent
 Stage II – T2-3 N0 M0; five-year survival 53 percent
 Stage III – T4 N0-1 M0, T1-4 N1 M01-, and T1-4 N0-1 M1; five-year survival 29
percent

Treatment:
Complete surgical resection is technically challenging and requires
peritonectomy with resection of involved organs.
Combined-modality approaches using surgery and chemotherapy hint of a
brighter future.

Primary Peritoneal Serous Carcinoma
Primary peritoneal serous carcinoma is an epithelial tumor that arises
from the peritoneum.
At histopathologic analysis, it resembles a malignant ovarian surface
epithelial stromal tumor.
Primary peritoneal serous carcinoma is thought to arise from
extraovarian mesothelium that has mullerian potential, making it a
unique clinicopathologic entity distinct from its ovarian counterpart.

Primary Peritoneal Serous Carcinoma
Patients typically present with complaints of abdominal distention,
pain, and fullness; increasing abdominal girth; and gastrointestinal
symptoms such as nausea and vomiting.
Clinically, the majority of patients have ascites and elevation of
serum levels of cancer antigen CA- 125.

Classification of Secondary Tumors and Tumor-like Lesions of the Peritoneum
I. Metastatic neoplasms
 Carcinomatosis
 Pseudomyxoma peritonei
 Lymphomatosis
 Sarcomatosis
II. Infectious and inflammatory lesions
 Granulomatous peritonitis
 Inflammatory pseudotumor
 Sclerosing encapsulating peritonitis
III. Miscellaneous tumors and tumorl-ike lesions
 Endometriosis
 Gliomatosis peritonei
 Osseous metaplasia
 Cartilagenous metaplasia
 Melanosis
 Splenosis

Peritoneal carcinomatosis:
 This is a common terminal event in many cases of carcinoma of the stomach,
colon, ovary or other abdominal organs and also of the breast and bronchus.
 The peritoneum, both parietal and visceral, is studded with secondary growths
and the peritoneal cavity becomes filled with clear, straw-colored or blood-
stained ascitic fluid.

The main forms of peritoneal metastases are:
 Discrete nodules – by far the most common variety;
 Plaques varying in size and colour;
 Diffuse adhesions – this form occurs at a late stage of the disease and gives
rise, sometimes, to a ‘frozen pelvis’.

Differential diagnosis
 Early discrete tubercles common in tuberculous peritonitis are greyish and
translucent and closely resemble the discrete nodules of peritoneal
carcinomatosis.
 Fat necrosis can usually be distinguished from a carcinomatous nodule by its
opacity.
 Peritoneal hydatids can also simulate malignant disease after rupture of a
hydatid cyst, with seeding of daughter cysts.

Treatment
Ascites caused by carcinomatosis of the peritoneum may respond to
systemic or intraperitoneal chemotherapy or to endocrine therapy in the
case of hormone receptor-positive tumours.

Pseudomyxoma Peritonei
A rare malignant process of the peritoneal cavity that
characteristically arises from a ruptured ovarian or
appendiceal adenocarcinoma.
The peritoneum becomes coated with a mucus-secreting
tumor that fills the peritoneal cavity with tenacious,
semisolid mucus and large loculated cystic masses.

Pseudomyxoma peritonei is most prevalent in
women between 50 and 70 years of age.
It is often asymptomatic until very late in its course,
and patients often experience a global deterioration
in their health long before the diagnosis of
pseudomyxoma peritonei is made.

Symptoms and signs

CT may demonstrate posterior
displacement of the small
intestine, loculated collections of
fluid-density material, and
scalloping of intra-abdominal
organs due to extrinsic
compression by adjacent
peritoneal implants.

The management of these patients includes drainage of
the mucus and intraperitoneal fluid and cytoreduction
of the primary and secondary tumor implants, including
peritonectomy and omentectomy.
For those tumors originating from an appendiceal
adenocarcinoma, a right colectomy is also performed.
Ovarian malignancies are treated with total abdominal
hysterectomy and bilateral salpingo-oophorectomy as
well as cytoreduction.

In the setting of an indeterminate site of origin, a
right colectomy and resection of the omentum along
with bilateral oophorectomy and cytoreduction
surgery are performed.
Postoperative adjuvant therapy has included the use
of intraperitoneal 5-fluorouracil, mitomycin C, and
oxiliplatin, as well as intraperitoneal mucolytics,

Tumors of the omentum
Omental cysts
 Pathology
Most cysts of the omentum are of lymphatic mesothelioma origin.
All are rare.

Omental cysts
Cystic lymphangioma
In childhood, omental cysts are usually caused by developmental abnormalities of
the lymphoid tissue, such as obstruction of the lymphatic channels or by growth
of congenitally misplaced lymphatic tissue.
They are variously called chylous cysts, cystic hygromas, or cystic lymphangiomas,
and are benign.
They vary greatly in size, and can be unilocular or multilocular.
Histologically each cyst has an endothelial lining similar to cystic hygroma of the
neck, and contains many foamy macrophages, giving the fluid a milky
appearance.

Omental cysts
Cystic mesothelioma
Omental cysts of mesothelial origin occur almost exclusively in adult life, usually
in women under the age of 50 years.
Although they are benign, local recurrence often occurs after surgical excision.
They appear as large multicystic masses similar to cystic lymphangiomas, but
histologically they are lined by flattened or cuboidal mesothelial cells and the cyst
fluid is clear, containing mucopolysaccharides.
Although the aetiology is unknown there is no association with asbestos exposure.

Omental cysts
Dermoid cysts
As with dermoid cysts elsewhere in the body, omental dermoid cysts are lined
with squamous epithelium and may contain epithelial structures such as hair and
teeth.
Pseudocysts
Omental pseudocysts are caused by fat necrosis or abdominal trauma with
haematoma formation. They are lined with fibrous tissue and contain blood-
stained fluid.

Omental cysts
Clinical features and treatment
Many omental cysts are small and asymptomatic and may only be discovered
incidentally at laparotomy or autopsy.
Large cysts may present with diffuse abdominal distension or as asmooth, mobile,
palpable mass in the lower midline. Characteristically they are non-tender unless
complicated by torsion of the omentum or intestinal obstruction.
Plain radiographs of the abdomen may demonstrate a soft tissue shadow and
barium studies may show displacement of bowel.
The differential diagnosis includes mesenteric, peritoneal, or retroperitoneal cysts
and tumours but the diagnosis is usually made at laparotomy.
Treatment consists of surgical excision of the cyst.

Solid tumors of the omentum
Pathology
Secondary tumor
The vast majority of omental neoplasms are metastatic carcinomas
arising from ovary, bowel, or pancreas and these are often associated with
abdominal ascites.
The rare, diffuse, malignant mesothelioma of the peritoneum which is
associated with the exposure to fibrous minerals such as asbestos also
consistently involves the omentum.

Pathology
Primary tumor
 Primary solid tumors of the omentum are exceptionally rare and may
be benign or malignant.
 The majority are of smooth muscle origin.
 Malignant potential is difficult to predict from the histology but
approximately one-third are frankly malignant.
 Before making a diagnosis of primary smooth muscle tumour of the
omentum, leiomyosarcoma of the uterus or gastrointestinal tract giving
rise to omental metastases must be carefully excluded.
 Other rare primary omental tumors include fibroma, fibrosarcoma,
lipoma, and liposarcoma.
 Infantile myxoid hamartomas, found in infants under 1 year old, consist
of multiple nodular lesions which show histological resemblance to
myxoid liposarcoma; the clinical course is invariably benign.

Clinical features and treatment
Benign primary tumours of the omentum, when sufficiently large,
present with a palpable abdominal mass or diffuse distension and require
surgical excision.
Malignant primary omental tumours are highly invasive and often present
late with involvement of adjacent organs. Radical surgical excision of both
the omentum and the involved organs may be required, but often
palliative surgery is the only treatment option.

Retroperitoneal neoplasms
The retroperitoneum is a large potential space bounded
anteriorly by the posterior peritoneum, posteriorly by
the spine and back muscles, superiorly by the
diaphragm, inferiorly by the levators, and laterally by the
flank muscles at the level of the anterior superior spine
of the iliac crest to the tip of the twelfth rib.

In this vast potential space, retroperitoneal masses tend
to become very large before producing signs or
symptoms, thus accounting for the poor prognosis for
most malignant tumors arising there.
Although the pancreas, kidneys, ureters, and adrenals
are retroperitoneal structures, neoplasms of these
organs are not generally included in the analysis of
retroperitoneal neoplasms.

With rare exceptions, retroperitoneal neoplasms are
sarcomas, lymphomas, or benign lesions.
Retroperitoneal sarcomas are rare, representing only about
0.1 to 0.2 per cent of all malignancies overall and only about
10 to 15 per cent of all soft-tissue sarcomas. They form
approximately 40 per cent of all retroperitoneal masses.

Retro-peritoneal sarcoma
Sarcomas constitute a heterogeneous group of rare solid
tumors of mesenchymal cell origin with distinct
clinical and pathological features.
They are divided into two broad categories:
 Soft tissue sarcomas
 Bone sarcomas

Sarcomas collectively account for approximately 1% of all
adult malignancies and 15% of pediatric malignancies.
The true incidence of STS is underestimated, especially
because a large proportion of patients with
gastrointestinal stromal tumors (GISTs) may not have
been included in tumor registry database before 2001.

The most common subtypes of STS are undifferentiated
pleomorphic sarcoma, GISTs, liposarcoma,
leomyosarcoma, synovial sarcoma and malignant
peripheral nerve sheath tumors.
The anatomic site of the primary disease represents an
important variable that influences treatment and
outcome. Extremities (43%), trunk (10%),
visceral(19%), retroperitoneal (15%) and head and
neck (9%) are the most common primary sites.

Approximately 80 percent of the neoplasms that arise
within the retroperitoneal space are malignant.
Furthermore, the majority of patients who present with
a primary retroperitoneal, extravisceral, unifocal soft
tissue mass will be found to have a sarcoma.

In adults, the most common histologic types of
retroperitoneal STS are liposarcomas and
leiomyosarcomas, followed by pleomorphic
undifferentiated sarcoma/malignant fibrous
histiocytoma.
A variety of other histologic types may be observed, but
they are much less common in the retroperitoneum
than in other primary sites.

Among children, the most common histologic types of
retroperitoneal STS are extraskeletal Ewing
sarcoma/primitive neuroectodermal tumors [PNET],
alveolar rhabdomyosarcoma, and fibrosarcoma
Approximately one-half of all retroperitoneal sarcomas
are high-grade tumors, although this varies according
to histology. The majority of retroperitoneal
liposarcomas are low- to intermediate-grade lesions.

STS most commonly metastasize to the lungs ; tumors
arising in the abdominal cavity more commonly
metastasize to the liver and peritoneum.
Management of STS in adult patients is addressed from
the perspective of the following disease subtypes:
 STS of extremity, superficial/ trunk, or head and neck.
 Retroperitoneal or intra-abdominal STS.
 GISTs
 Desmoid tumors
 Rabdomyosarcoma.

Genetic cancer syndromes with predisposition to
STS:
 Li-Faumeni syndrome (TP53 germline mutation).
Associated with RMS, fibrosarcoma and
undifferentiated pleomorphic sarcoma.
 Gardner syndrome (desmoid tumors)
 Carney-Stratakis syndrome (GISTs and
paragangliomas)

WORKUP:
Prior to the initiation of therapy, all patients should be
evaluated and managed by multidisciplinary team.
 History and physical examination.
 Chest, abdomen and pelvis CT with contrast
 MRI may add some data

WORKUP:
Criteria for unresectability — Radiographic findings that indicate
unresectability include:
 Extensive vascular involvement (aorta, vena cava and/or iliac vessels), although
involvement of the vena cava and iliac veins is a relative rather than absolute
contraindication, as these vessels can often be replaced with interposition
grafts
 Peritoneal implants
 Distant metastases
 Involvement of the root of the mesentery (specifically, the superior mesenteric
vessels)
 Spinal cord involvement

WORKUP:
 Biopsy:
Pre-resection biopsy is not necessarily required ; consider
biopsy if there is suspicion of malignancy other than
sarcoma.
Image-guided (U/s or CT) core needle biopsy is preferred
 Patients with personal/family history suggestive of Li-
Fraumeni syndrome should be considered for further
genetic assessment.

Staging:
 Retroperitoneal sarcomas are staged using the same TNM system
as is used for extremity STS. However, the ability of the TNM
staging system to discriminate outcomes is limited.
 Several studies have found no prognostic role for tumor size in
retroperitoneal sarcoma.
 Given the importance of histologic grade and resection margins
in the prognosis of retroperitoneal STS, an alternative staging
system has been proposed that incorporates these features as
well as the presence or absence of metastatic disease. However,
this staging system is not in widespread use.

Staging:
The Dutch/Memorial Sloan-Kettering cancer center
classification system for retroperitoneal soft
tissue sarcomas
Classification Definition
Stage I Low-grade, complete resection, no metastases
Stage II High-grade, complete resection, no metastases
Stage III Any grade, incomplete resection, no metastases
Stage IV Any grade, any resection, distant metastases

TREATMENT
Surgical resection:
Surgical resection has traditionally been the only potentially
curative treatment for a localized retroperitoneal STS.
The ability to perform a complete surgical resection at the
time of initial presentation is the most important
prognostic factor for survival.
The usual reasons for unresectability are extensive vascular
involvement or the presence of multiple peritoneal
implants.

TREATMENT
Surgical resection:
The primary oncologic goal is complete resection with
microscopically negative margins (R0 resection).
However, the large size of most retroperitoneal tumors,
coupled with the inability to obtain wide margins due to
anatomic constraints make this goal difficult to achieve.
In clinical practice, many resections are grossly complete but
with microscopically positive margins (R1 resection)

TREATMENT
Surgical resection:
Resection of adjacent organs such as the small bowel, colon
or kidney is often required to achieve a complete resection
and bowel preparation and evaluation of kidney function
should be performed prior to exploration.
Liberal en-bloc resection of adjacent viscera may allow a
subset of patients to achieve wide, macroscopically
negative surgical margins who might otherwise have been
considered unresectable.

TREATMENT
Surgical resection:
Role of debulking surgery —
There is no survival benefit for incomplete resection (a
"debulking" procedure) in patients with unresectable
retroperitoneal STS.

TREATMENT
Adjunctive RT:
In contrast to extremity STS in which the most common site
of first recurrence is a distant site, the primary pattern of
treatment failure after resection of a retroperitoneal STS is
local.
Adjunctive radiation therapy (RT) can be administered
following resection (adjuvant RT). However, increasingly,
preoperative RT is being chosen for large high-grade or
intermediate-grade STS.

TREATMENT
Adjunctive RT:
Adjuvant RT
It is often difficult to deliver postoperative radiation therapy
because the bowel and other organs fall into the resection cavity;
however, newer techniques such as intensity-modulated RT
(IMRT) and proton beam irradiation make it more feasible but
the therapeutic ratio is probably still more favorable with
preoperative RT.
Nevertheless, it is reasonable to consider the use of postoperative
RT if it can be delivered safely.

TREATMENT
Adjunctive RT:
Adjuvant RT
In the postoperative setting, radiation doses to the tumor bed are often
limited by the large field size and the proximity and tolerance of
surrounding radiosensitive normal structures, such as the liver and
bowel.
In fact, many multidisciplinary sarcoma groups do not routinely offer
postoperative RT to patients with resected retroperitoneal sarcomas
because of significant concerns about the narrow therapeutic ratio.

TREATMENT
Adjunctive RT:
Preoperative RT
The delivery of RT prior to surgery, with or without
intraoperative RT (IORT) at the time of resection, may
permit the safe delivery of higher RT doses than are
possible in the postoperative setting

TREATMENT
Adjunctive RT:
Preoperative RT
There are several theoretical advantages for preoperative as compared to
postoperative RT for retroperitoneal STS :
 The main advantage of preoperative RT is that the gross tumor volume
can be precisely defined for radiation treatment planning, allowing
accurate targeting of the radiation volume around the tumor.
 The tumor itself can act to displace small bowel from the high-dose
radiation field, resulting in safer and less toxic treatment.

TREATMENT
Adjunctive RT:
Preoperative RT
There are several theoretical advantages for preoperative as
compared to postoperative RT for retroperitoneal STS :
 Higher RT doses can be delivered to the actual tumor field, since
bowel adhesions to tumor are less likely compared to the
postoperative setting.
 The risk of intraperitoneal tumor dissemination at the time of
the operation may be reduced by preoperative RT.

TREATMENT
Adjunctive RT:
Preoperative RT
There are several theoretical advantages for preoperative as compared to
postoperative RT for retroperitoneal STS :
 Radiation is considered to be biologically more effective in the
preoperative setting.
 It is possible that an initially unresectable tumor may be converted to
one that is potentially resectable for cure.
These advantages may result in an improvement in the therapeutic
ratio when RT is administered preoperatively.

Outcomes and prognostic factors
Retroperitoneal sarcomas have a substantially less satisfactory
outcome than soft tissue sarcomas (STS) at other sites, such as
the extremities or trunk.
Several factors contribute to poor outcome and a high rate of
recurrence:
 Retroperitoneal STS are often large at diagnosis and anatomically
situated such that wide resection is often not achievable.
 Even with complete resection, retroperitoneal liposarcomas tend
to do worse than extremity liposarcomas, independent of tumor
size, grade, or surgical margin.

Retroperitoneal sarcomas have a substantially less satisfactory
outcome than soft tissue sarcomas (STS) at other sites, such as
the extremities or trunk.
Several factors contribute to poor outcome and a high rate of
recurrence:
 The surrounding normal tissues (liver, kidney, gastrointestinal
tract, spinal cord) have relatively low tolerance for radiation
therapy (RT). As a result, radiation dose levels must be kept
below those typically employed for extremity sarcomas.

In contrast to extremity sarcomas, 90 percent of first recurrences
are local. Eventually, distant metastases develop in 20 to 30
percent . The main sites of distant metastases are liver and lungs.
Local recurrence rates are higher with high-grade (poorly
differentiated) tumors, liposarcoma histology, and in patients
with positive resection margins.

Recurrent retroperitoneal sarcoma

Peritoneum, mesenetry and retroperitoneal tumors 2

Peritoneum, mesenetry and retroperitoneal tumors 2

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