The Challenge of Diagnosing Metastases to the Gastrointestinal Tract With a Linitis Plastica Appearance on Cross-Sectional Imaging: A Case- Series Presentation and a Review of Literature

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.