Imaging in Peritoneal Neoplasms: Diagnostic Advances and Multimodal Treatment Strategies

Introduction

Malignant peritoneal neoplasms, encompassing primary tumors like peritoneal mesothelioma and secondary metastatic spread (peritoneal carcinomatosis), represent a complex clinical challenge with historically poor prognoses. Traditional management focused on palliative care to alleviate symptoms of ascites, bowel obstruction, and pain. However, advancements in multimodal strategies- integrating cytoreductive surgery (CRS), hyperthermic intraperitoneal chemotherapy (HIPEC), and systemic therapies- have shifted the paradigm toward curative intent in select patients. Central to this evolution is the role of advanced imaging, which enables precise diagnosis, staging, and therapeutic planning. This review explores the critical importance of imaging modalities in diagnosing malignant peritoneal neoplasms, their integration into multimodal treatment protocols, and emerging innovations reshaping patient outcomes.

The Shift from Palliative Care to Multimodal Therapy

Historically, malignant peritoneal neoplasms were deemed incurable due to their diffuse nature and resistance to conventional chemotherapy. Palliative approaches, including paracentesis or systemic chemotherapy, aimed to prolong survival but rarely improved long-term outcomes. The advent of CRS-HIPEC-aggressive surgical debulking combined with heated intraperitoneal chemotherapy- has transformed management, offering 5-year survival rates of 30–50% in eligible patients with peritoneal metastases from colorectal or ovarian cancers. This shift demands accurate preoperative imaging to identify candidates for curative-intent therapy while excluding those with unresectable disease. Consequently, radiology has become indispensable in stratifying patients, guiding surgical planning, and monitoring therapeutic response.

Imaging Modalities: Strengths and Limitations

Computed Tomography (CT)

CT remains the first-line imaging modality for evaluating peritoneal malignancies due to its widespread availability, rapid acquisition, and ability to assess both peritoneal and visceral involvement. Multidetector CT (MDCT) with intravenous and oral contrast enhances the detection of peritoneal deposits, mesenteric thickening, and omental caking. However, its sensitivity for subcentimeter nodules-critical for surgical planning- is limited (50–70%), particularly in regions like the small bowel mesentery or pelvis. False negatives may occur due to similar attenuation between the tumor and adjacent structures, underscoring the need for complementary modalities.

Magnetic Resonance Imaging (MRI)

MRI excels in soft-tissue contrast, making it superior for detecting small peritoneal implants and differentiating malignant from benign lesions. Diffusion-weighted imaging (DWI) highlights cellular tumors by restricting water movement, improving sensitivity to 85- 90% for lesions >5 mm. Protocols incorporating dynamic contrast-enhanced (DCE) sequences further characterize vascularity and tumor response. Despite advantages, MRI’s longer acquisition time, cost, and contraindications (e.g., pacemakers) limit its use as a frontline tool.

Positron Emission Tomography/CT (PET/CT)

PET/CT combines metabolic and anatomic data, using radiotracers like 18F-FDG to identify hypermetabolic peritoneal deposits. It is particularly valuable for staging high-grade malignancies (e.g., ovarian cancer) and detecting occult distant metastases, which may contraindicate CRS-HIPEC. However, false positives from inflammation or post-surgical changes and poor resolution for subcentimeter lesions reduce its standalone utility.

Ultrasound and Emerging Techniques

Transabdominal and endoscopic ultrasound (EUS) are less commonly used but offer real-time imaging for guided biopsies in suspected peritoneal disease. Emerging techniques like contrast-enhanced ultrasound (CEUS) and artificial intelligence (AI)-driven image analysis show promise in improving lesion detection and reducing interpreter variability.

Challenges in Imaging Peritoneal Malignancies

Despite technological advancements, imaging peritoneal neoplasms remains fraught with challenges. The peritoneum’s complex anatomy, with its multiple recesses and folds, often harbors occult disease. Differentiating benign entities (e.g., peritoneal tuberculosis) from malignant spread requires correlation with clinical history and biomarkers. Moreover, post-treatment changes—such as fibrosis after HIPEC- mimic residual disease on imaging, complicating response assessment. Multidisciplinary tumor boards integrating radiologic, pathologic, and clinical data are essential to mitigate these limitations.

Integrating Imaging into Multimodal Treatment Planning

Accurate imaging directly influences therapeutic decision-making. For instance, the Peritoneal Carcinomatosis Index (PCI), calculated from preoperative CT or MRI, quantifies tumor burden across 13 abdominal regions. A PCI <20 often qualifies patients for CRS-HIPEC, while higher scores may indicate palliative approaches. Post-treatment, functional MRI or FDG-PET/CT monitors recurrence, though distinguishing residual tumor from inflammation remains challenging. Emerging protocols leverage radiomics- quantitative analysis of imaging features- to predict treatment response and personalize follow-up intervals.

Future Directions: Precision Imaging and Beyond

Innovations in hybrid imaging (e.g., PET/MRI), molecular-targeted tracers, and AI-driven analytics are poised to revolutionize peritoneal malignancy management. For example, fibroblast activation protein (FAP)-targeted PET tracers improve specificity for stromal-rich tumors, while AI algorithms enhance lesion detection in low-contrast CT datasets. These tools, combined with liquid biopsies for early recurrence detection, may soon enable truly personalized therapeutic strategies.

Conclusion

The management of malignant peritoneal neoplasms has evolved from palliation to curative intent, driven by multimodal therapies and advances in imaging. CT, MRI, and PET/CT each play distinct roles in diagnosis, staging, and surveillance, though no single modality is flawless. A tailored, multidisciplinary approach leveraging the strengths of multiple imaging techniques is critical to optimizing patient outcomes. As precision imaging and AI redefine diagnostic accuracy, radiologists and oncologists must collaborate closely to harness these innovations, ensuring that patients receive timely, evidence-based care in this rapidly evolving field.

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