Peritoneal carcinomatosis (PC) refers to malignant epithelial cells that spread to the peritoneum, principally from abdominal malignancies. Until recently, PC prognosis has been considered ill-fated, with palliative therapies serving as the only treatment option. New locoregional treatments are changing the outcome of PC, and imaging modalities have a critical role in early diagnosis and disease staging, determining treatment decision making strategies. The aim of this review is to provide a practical approach for detecting and characterizing peritoneal deposits in cross-sectional imaging modalities, taking into account their appearances, including the secondary complications, the anatomical characteristics of the peritoneal cavity, together with the differential diagnosis with other benign and malignant peritoneal conditions. Among the cross-sectional imaging modalities, computed tomography (CT) is widely available and fast; however, magnetic resonance (MR) performs better in terms of sensitivity (92% vs. 68%), due to its higher contrast resolution. The appearance of peritoneal deposits on CT and MR mainly depends on the primary tumour histology; in case of unknown primary tumour (3–5% of cases), their behaviour at imaging may provide insights into the tumour origin. The timepoint of tumour evolution, previous or ongoing treatments, and the peritoneal spaces in which they occur also play an important role in determining the appearance of peritoneal deposits. Thus, knowledge of peritoneal anatomy and fluid circulation is essential in the detection and characterisation of peritoneal deposits. Several benign and malignant conditions show similar imaging features that overlap those of PC, making differential diagnosis challenging. Knowledge of peritoneal anatomy and primary tumour histology is crucial, but one must also consider clinical history, laboratory findings, and previous imaging examinations to achieve a correct diagnosis. In conclusion, to correctly diagnose PC in cross-sectional imaging modalities, knowledge of peritoneal anatomy and peritoneal fluid flow characteristics are mandatory. Peritoneal deposit features reflect the primary tumour characteristics, and this specificity may be helpful in its identification when it is unknown. Moreover, several benign and malignant peritoneal conditions may mimic PC, which need to be considered even in oncologic patients.

Several solid lesions can be found within the pancreas mainly arising from the exocrine and endocrine pancreatic tissue. Among all pancreatic malignancies, the most common subtype is pancreatic ductal adenocarcinoma (PDAC), to a point that pancreatic cancer and PDAC are used interchangeably. But, in addition to PDAC, and to the other most common and well-known solid lesions, either related to benign conditions, such as pancreatitis, or not so benign, such as pancreatic neuroendocrine neoplasms (pNENs), there are solid pancreatic lesions considered rare due to their low incidence. These lesions may originate from a cell line with a differentiation other than exocrine/endocrine, such as from the nerve sheath as for pancreatic schwannoma or from mesenchymal cells as for solitary fibrous tumour. These rare solid pancreatic lesions may show a behaviour that ranges in a benign to highly aggressive malignant spectrum. This review includes cases of an intrapancreatic accessory spleen, pancreatic tuberculosis, solid serous cystadenoma, solid pseudopapillary tumour, pancreatic schwannoma, purely intraductal neuroendocrine tumour, pancreatic fibrous solitary tumour, acinar cell carcinoma, undifferentiated carcinoma with osteoclastic-like giant cells, adenosquamous carcinoma, colloid carcinoma of the pancreas, primary leiomyosarcoma of the pancreas, primary and secondary pancreatic lymphoma and metastases within the pancreas. Therefore, it is important to determine the correct diagnosis to ensure optimal patient management. Because of their rarity, their existence is less well known and, when depicted, in most cases incidentally, the correct diagnosis remains challenging. However, there are some typical imaging features present on cross-sectional imaging modalities that, taken into account with the clinical and biological context, contribute substantially to achieve the correct diagnosis.

This review provides an overview of the cross-sectional imaging features of gastrointestinal (GI) metastases presenting with a linitis plastica (LP) pattern and illustrates these findings through a series of cases from various primary tumors. It also addresses key diagnostic challenges, with particular attention to differential diagnosis. The term linitis plastica (LP) refers to the macroscopic appearance of a hollow organ with diffuse mural tumor infiltration, leading to loss of parietal distensibility. Although rare, primary LP can occur throughout the gastrointestinal (GI) tract. First described in the stomach—the most common site—it is typically associated with undifferentiated adenocarcinoma composed of poorly cohesive cells, often with signet ring morphology. Beyond primary GI tumors, LP-like metastases may also arise from extragastrointestinal primaries, most notably breast carcinoma (particularly the lobular subtype), as well as urinary bladder and prostate carcinomas. LP-like GI metastases typically manifest as circumferential, enhancing wall thickenings with exaggerated zonal anatomy and luminal narrowing. Due to diffuse parietal tumor infiltration—often with mucosal preservation—the submucosa and serosa appear disproportionately thickened and show greater enhancement relative to the muscularis propria (MP). This specific imaging appearance is known as the malignant target sign, which must be distinguished from the benign target sign, where the most prominent low-density layer corresponds to edematous submucosa. Additional key features include homogeneous enhancement with loss of layer differentiation on delayed-phase imaging and a concentric ring pattern on MR. Secondary findings may also be present, such as intestinal obstruction and concomitant peritoneal carcinomatosis (PC). Gastrointestinal metastases with an LP pattern present a significant diagnostic challenge, as they can mimic both primary tumors and benign inflammatory or infectious conditions. Accurate diagnosis is critical because management strategies differ substantially. Since the mucosa is often spared, endoscopy and superficial biopsies may yield false-negative results. Therefore, while immunohistochemistry (IHC) remains essential for confirmation, radiologists play a pivotal role in raising suspicion for LP-like GI metastases and recommending deep, extensive biopsies to obtain adequate representative tissue. Furthermore, in cases of an unknown primary tumor, recognition of the LP pattern can provide important clues to the potential site of origin.

Among cross-sectional imaging modalities, computed tomography (CT) is more available and faster; however, magnetic resonance (MR) performs better in terms of sensitivity and specificity, due to its higher contrast resolution. The appearance of peritoneal deposits on CT and MR depends mainly on the primary tumour histology: in case of unknown primary tumour (3-5% of cases), their behaviour at imaging may provide insights on the tumour origin. The time-point of tumour evolution, previous or ongoing treatments and the peritoneal spaces where they occur, also play an important role in determining the appearance of peritoneal deposits. Thus, knowledge of peritoneal anatomy and fluid circulation is mandatory in detection and characterization of peritoneal deposits. Several benign and malignant conditions may show similar imaging features that overlap those of PC, making the differential diagnosis challenging. Clinical history, laboratory findings and previous imaging examinations must be considered to achieve the correct diagnosis.

Immune checkpoint inhibitors (ICIs) improve survival in multiple malignancies but may induce immune-related adverse events (irAEs), including immune-related bronchiolitis (IRB). Radiologic patterns frequently overlap with infectious diseases, particularly tuberculosis (TB), whose reactivation risk may be increased by ICIs via disruption of granuloma integrity. Differentiation between IRB and TB is challenging, especially in patients from endemic areas. We report the case of a 53-year-old Turkish man with metastatic clear-cell renal cell carcinoma, who underwent right nephrectomy followed by nivolumab plus ipilimumab. Four months after treatment, he developed fatigue, dyspnea, productive cough, and weight loss. Chest CT scan showed centrilobular nodules with a tree-in-bud pattern. QuantiFERON® testing was positive. Bronchoalveolar lavage showed lymphocyte predominance with no infectious or neoplastic cells. Transbronchial biopsy demonstrated non-caseating granulomas. PCR for Mycobacterium tuberculosis was negative, and cultures were pending. Given the overlap between IRB and TB, empirical quadruple anti-TB therapy and inhaled corticosteroids were initiated and immunotherapy was temporarily discontinued. After 2 months, given negative mycobacterial cultures and significant hepatotoxicity, isoniazid was discontinued, rifampicin was carefully reintroduced under close monitoring, and the total anti-TB treatment duration was shortened to 4 months. The patient subsequently showed gradual improvement in respiratory symptoms, biomarkers, and radiologic findings. This case illustrates the challenge of distinguishing IRB from TB in ICI-treated patients. Empirical anti-TB therapy may be warranted in high-risk settings despite absent microbiological confirmation but carries toxicity and complicates oncologic management. Pre-treatment latent TB screening and multidisciplinary decision-making are essential to balance infection control with cancer therapy.

BACKGROUND This review aims to summarize the imaging features on cross-sectional imaging mo-dalities of metastases to the gastrointestinal tract (GI) with a linitis plastica (LP) pat-tern and to present a series of cases from different primary tumours. Challenging questions concerning their diagnosis will be discussed in detail, including their differ-ential diagnosis. The term LP is to describe the macroscopic appearance of any hollow organ with dif-fuse mural tumour infiltration, responsible for the loss of parietal distensibility. Pri-mary LP, however rare, may be found throughout the GI tract. First described in the stomach, which represents the most frequent location, it is associated with undifferen-tiated adenocarcinoma with poorly cohesive cells, often presenting signet ring fea-tures. In addition to primary GI LP, LP-like metastases may occur in association with prima-ry tumours arising beyond the GI tract, namely breast (especially the lobular type), urinary bladder and prostate carcinomas. MAIN TEXT LP-like GI metastases appear as circumferential and enhancing thickenings of the GI, with an exaggerated zonal anatomy and a narrowed lumen. As a result of the diffuse parietal tumour infiltration that frequently preserves the mucosa, the infiltrated sub-mucosa and serosa appear disproportionately expanded with increased enhancement compared to the muscularis propria (MP). This appearance constitutes the malignant target sign, which is to be differentiated from its non-tumoral counterpart, the benign target sign, where the low density intervening and most prominent layer is the edem-atous submucosa. A homogeneous enhancement with loss of layer differentiation at the delayed phase and a concentric ring pattern on MR have also been described as key imaging features, in addition to associated findings, such as secondary intestinal occlusion and concom-itant peritoneal carcinomatosis (PC). CONCLUSIONS GI metastases with LP pattern cause a diagnostic challenge as they may mim-ic primary tumours as well as benign conditions such as inflammatory/infectious dis-eases. Achieving the correct diagnosis is crucial, as patient management differs. Since the mucosa may be spared, endoscopies and biopsies are frequently negative. Thus, alt-hough immunohistochemistry (IHC) studies are essential, radiologists play a para-mount role in suggesting LP-like GI metastases and proposing deep and extensive bi-opsies to obtain substantial representative tissue to confirm the diagnosis. Moreover, in the event of an unknown primary tumour, recognition of the LP pattern may be extremely helpful in suggesting possible primary tumours.