What is the diagnosis and treatment approach for peritoneal nodules?

Peritoneal Nodules: Diagnosis and Treatment

Diagnostic Approach

Peritoneal nodules require systematic evaluation through imaging, risk stratification, and tissue diagnosis to distinguish between benign, inflammatory, and malignant etiologies, with contrast-enhanced CT serving as the primary imaging modality. 1

Initial Imaging

• Contrast-enhanced abdominal and pelvic CT scan is the imaging modality of choice for detecting and characterizing peritoneal nodules, assessing their size, distribution, and relationship to surrounding structures 2, 1
• MRI may provide additional information when CT findings are indeterminate, particularly for distinguishing tissue characteristics 1
• FDG-PET/CT is useful for risk stratification in intermediate-risk lesions but should be reserved for nodules where malignancy probability is 10-70% based on initial assessment 3

Tissue Diagnosis

Core needle biopsy under image guidance (CT or ultrasound) is the standard diagnostic approach for peritoneal nodules >3 cm, using 14-16 gauge automated cutting needles with coaxial introducer to obtain 4-6 cores while targeting viable tumor tissue and avoiding necrotic areas 1. The diagnostic accuracy of this technique is 90-95% with specificity of 99% 1.

• For smaller or multiple peritoneal nodules, diagnostic laparoscopy with direct visualization and biopsy provides the highest diagnostic yield 2, 4
• EUS-guided FNA can be considered for peritoneal deposits visible on endoscopic ultrasound, particularly in patients with ascites, with successful diagnosis in 83% of cases 5
• All tissue samples must be fixed in formalin (never Bouin fixation) to preserve molecular analysis capability 2, 1
• Frozen tissue collection is encouraged for potential future molecular assessments 2

Critical Surgical Considerations

In cases of suspected GIST with tumor rupture or peritoneal contamination, careful surgical exploration for small peritoneal nodules is mandatory, as this denotes highly adverse prognosis 2. Abdominal washing during surgery may be an option in case of tumor rupture 2.

For ovarian cancer staging, careful examination of the abdominal cavity is required including biopsy of diaphragmatic peritoneum, paracolic gutters, pelvic peritoneum, and peritoneal washings 2. Up to 22% of apparent early-stage ovarian cancers will be upstaged through systematic evaluation of peritoneal surfaces 2.

Differential Diagnosis

The etiology of peritoneal nodules spans a broad spectrum:

Malignant Causes

• Peritoneal metastases from gastrointestinal, ovarian, or other primary malignancies represent the most common malignant etiology 6
• Primary peritoneal carcinoma, including high-grade serous carcinoma 2, 6
• Gastrointestinal stromal tumors (GIST) with peritoneal spread 2
• Pseudomyxoma peritonei from appendiceal tumors 7, 5
• Peritoneal mesothelioma 6

Benign/Inflammatory Causes

• Tuberculous peritonitis (particularly in endemic regions) 5
• Endosalpingiosis-leiomyomatosis peritonei 8
• Inflammatory nodules without specific etiology 5

Treatment Approach

Malignant Peritoneal Nodules

Multidisciplinary tumor board discussion involving pathologists, radiologists, surgeons, and medical oncologists is mandatory before proceeding with definitive treatment 2, 1.

Ovarian Cancer with Peritoneal Involvement

• Debulking surgery to remove as much gross tumor as possible is the primary treatment, with R0 resection as the goal 2
• Staging procedures include infracolic omentectomy, biopsy of peritoneal surfaces, and peritoneal washings 2
• Platinum-based chemotherapy (typically BEP regimen: bleomycin, etoposide, cisplatin) is the treatment of choice for advanced disease, with 3 cycles for completely resected disease and 4-5 cycles for macroscopic residual disease 2
• Positive peritoneal cytology in stage I disease signifies stage IC3 and may indicate need for adjuvant therapy 2

GIST with Peritoneal Spread

• Complete surgical excision without lymph node dissection is standard treatment for localized GIST 2
• If R0 surgery is not feasible, imatinib pretreatment is recommended to achieve cytoreduction and potentially less mutilating surgery 2
• Tumor rupture with peritoneal contamination carries highly adverse prognosis; abdominal washing during surgery may be considered 2

Pseudomyxoma Peritonei

• Cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy (HIPEC) is the standard treatment approach for pseudomyxoma peritonei from appendiceal tumors 7
• Preoperative evaluation must assess extent of peritoneal disease and patient fitness for major surgery 7

Benign/Inflammatory Nodules

• Tuberculous peritonitis requires anti-tuberculous therapy when PCR or culture confirms Mycobacterium tuberculosis 5
• Endosalpingiosis-leiomyomatosis peritonei may require surgical excision if symptomatic 8
• Inflammatory nodules without specific etiology typically require surveillance after exclusion of malignancy 5

Key Diagnostic Pitfalls

• Do not proceed with definitive surgery before obtaining tissue diagnosis for larger masses requiring multivisceral resection, as this allows proper surgical planning and may avoid unnecessary surgery for non-surgical diseases like lymphoma 1
• Avoid necrotic or hemorrhagic areas during biopsy planning by using imaging guidance to target the most cellular portions of the mass 1
• False-negative biopsy results occur in 6-20% of cases and do not exclude malignancy; repeat sampling or surgical resection may be required 3, 1
• In patients with known extrapulmonary malignancy, peritoneal nodules should be considered metastatic until proven otherwise 3
• Confocal laser endomicroscopy during laparoscopy can help discriminate benign from malignant nodules with 100% positive predictive value, though sensitivity is 75% 4