Schnitzler’s metastasis (SM) is an unusual and rare form of metastasis, typically seen in diffuse gastric cancer (DGC) [1]. The mode of spread is proposed to be either lymphatic or hematogenous, but still it is unclear. SM is characterized by narrowing of the rectal lumen, due to infiltration of the rectal submucosa by metastatic cancer cells, which leads to stenosis and ultimately bowel obstruction. Imaging modalities and colonoscopy usually help in diagnosis [2]. Management of these patients is usually palliative chemotherapy, but when they present with an intestinal obstruction, they might need a diversion stoma or self-expanding metallic stenting [3]. Here, we report a 54-year-old male patient who presented with intestinal obstruction, for which he underwent a diversion stoma in a hospital and was referred to us. He posed a significant diagnostic confusion to understand the etiology of the obstruction as the initial rectal biopsies were negative and inconclusive. He was finally diagnosed with SM and planned for palliative chemotherapy. Patient’s consent was taken when he was alive during the course of treatment for the publication of the photos and other clinical information in the journal.

A 54-year-old male with a history of lower abdominal pain associated with the passage of loose stools with mucus for a week was evaluated in a hospital. He underwent contrast-enhanced computed tomography, which identified circumferential symmetric wall thickening in the mid-to-distal rectum for a length of 6 cm with a maximum wall thickness of 12 mm, causing significant luminal narrowing (Fig. 1). There was heterogenous enhancement associated with the loss of mural stratification. Submucosal edema and meso-rectal fat stranding were also noted with the thickening of the meso-rectal fascia. Further, colonoscopy revealed mucosal thickening with luminal narrowing noted at 10 cm from the anal verge with no obvious growth or ulcer (Fig. 2). There was an associated reduced distensibility, and a biopsy was negative for malignancy. Then, the patient developed progressive abdominal distension and was diagnosed as having a large bowel obstruction due to a rectal malignancy. So, he underwent an emergency exploratory laparotomy, followed by a loop diversion stoma.

Further attempts to confirm the rectal cancer also proved futile, as the repeat biopsy was also negative for malignancy. His carcinoembryonic antigen was not elevated (1.49 ng/mL). Since he had a metal implant in his right hip, magnetic resonance imaging (MRI) could not be done. Thus, the positron emission tomography with 2-deoxy-2-[¹⁸F]fluoro-D-glucose (¹⁸F-FDG) classified his rectal lesion as mildly FDG avid with a standardized uptake value (SUV) maximum of 2.5. It also picked up a likely inflammatory smooth FDG-avid mucosal thickening in the antro-pyloric region of the stomach, with a maximum thickness of 6 mm and an SUV maximum of 3.9. In addition, the patchy areas of FDG uptake with an SUV maximum of 3.4 were also noted without any distinct lesion in the pancreas, which was commented on as doubtful autoimmune pancreatitis by the radiologists (Fig. 3).

Following this, the patient was referred to our institution at this conjuncture without a provisional diagnosis, even after an exhaustive evaluation. After thoroughly analyzing the patient and his previous records, he was examined under anesthesia, and a transrectal core needle biopsy was taken from the rectal stenosis, which was primarily extramucosal. He also underwent an upper gastrointestinal endoscopy, which revealed nodular thickened erythematous mucosa involving the fundus, body, and antrum with poor distensibility, suspicious of carcinoma of the stomach. Deeper biopsy taken from the stomach was positive for poorly differentiated adenocarcinoma with signet ring cells (SRCs), and the biopsy from the rectal stenosis was not conclusive. This finally brought us to ascertain a new term, “Schnitzler’s metastasis,” after reviewing the literature about this rare mode of metastatic spread from the carcinoma of the stomach to the rectal submucosa, leading to concentric rectal stenosis. The patient developed pulmonary embolism during his hospital stay, for which he was treated and then referred for palliative chemotherapy later. The 5-fluorouracil and cisplatin-based regimens were used. The patient survived for only 2 months after discharge from the hospital.

SM is an unusual and rare mode of distant spread of cancer cells to the rectal submucosa, usually from primary sites such as the stomach [1]. Stomach cancer is classified as diffuse, intestinal type, or mixed type. SM is peculiarly associated with DGC of the SRCs type. This type generally has a poor prognosis. Intestinal and DGC usually have a specific pattern of distant metastases. While intestinal type gastric cancer frequently tends to spread to the liver, the diffuse type is seen to metastasize commonly to the lung and peritoneum [2].

Distant metastasis of primary gastric cancer may occur through the hematogenous, lymphatic, or transcoelomic spread. Unlike the well-known condition of Blumer’s shelf, which is caused by the transcoelomic spread of cancer cells to the pouch of Douglas, SM causes narrowing of the rectum due to the spread of poorly differentiated cancer cells within the rectal submucosa through the bloodstream or lymphatic system [1].

Fernet et al. [4] speculated that this occurrence probably resulted from the milking force associated with peristalsis and antiperistalsis. He described five cases of the linitis plastica type of intramural tumor that spread along the alimentary tract among 150 patients with gastric cancer. In one of their five patients, the rectum was involved. These researchers reported that such intramural spread was caused by the milking of tumor cells via small longitudinal lymphatic channels, especially along the submucosa, resulting from peristalsis and antiperistalsis [4]. However, the affinity of the SRCs for the rectal submucosa cannot be adequately explained by this mechanism.

The strange link or affinity for DGC to pick up the rectal submucosa as a site for distant metastasis remains unexplained. This could be primarily related to the mechanism of dissemination of DGC. DGC is characterized by the loss of a functional cadherin 1 (CDH1) gene encoding for the adherens junction protein E-cadherin. The attenuated function of E-cadherin results in tumor progression and the dissemination of SRC to various regions through lymphatic permeation. Further, the development of invasive properties in the poorly differentiated cells, through which they spread into the submucosa and deeper layers, remains a crucial step in the malignant progression of DGC. This is facilitated by several genomic alterations and some changes in the tumor environment, which correlate with the aggressive nature of these tumors. Cancer-associated fibroblasts also play an important role in enhancing the migration of DGC cells and altering the extracellular matrix [5]. This might explain this unusual mode of metastasis to the rectal submucosa. However, further studies might be needed to establish this peculiar mechanism of spread associated with DGC.

Only 11 case reports of SM to the rectum where the present study, have been published about this rare phenomenon in the literature [2,6–15]. Similar secondary neoplastic infiltration of the colon has also been observed with DGC [16]. One case report of pancreatic malignancy causing SM has also been reported in the literature [2].

Almost all of these patients present with features of intestinal obstruction due to concentric rectal stenosis. They may also present with or without co-existing dyspepsia, early satiety, vomiting, and other symptoms suggestive of stomach malignancy. Since DGC with SRC type is the most common etiology, these vague symptoms can be easily missed or even absent, resulting in an advanced presentation like intestinal obstruction due to SM. In our case, the cause of the intestinal obstruction due to the rectal stenosis could be ascertained only after the oesophagogastroduodenoscopy (OGD) biopsy confirmed the stomach malignancy, as he did not have any upper gastrointestinal symptoms. This posed significant diagnostic uncertainty.

This lesion can present either in a synchronous or metachronous fashion. To identify synchronous lesions, all gastric adenocarcinoma patients, especially those with SRC types, should undergo a mandatory digital rectal examination to look for not only Blumer shelves but also any concentric extramucosal rectal stenosis in the form of SM. Also, on the contrary, any suspicious rectal stenosis with normal mucosa should undergo an OGD to rule out linitis plastica of the stomach. It also applies to metachronous lesions that arise after the patient has undergone a gastrectomy for a poorly differentiated adenocarcinoma with SRC type and in the follow-up period. Case reports by Olano et al. [7] and Okugawa et al. [8] both describe metachronous SM after the completion of gastrectomy.

Colonoscopy or sigmoidoscopy usually shows luminal narrowing at the site of stenosis with edematous mucosa without any mucosal lesion, as the submucosa is involved by tumor cells. Special mention should be made about the decreased distensibility of the lumen in the endoscopy and the deeper biopsy necessary to confirm the diagnosis both in the stomach and the rectum, as the superficial biopsies usually turn negative for malignancy.

Computed tomography (CT) is very helpful in diagnosing this rare condition with its concentric rectal thickening exhibited as a characteristic “onion ring” appearance. This is also referred to as the malignant target sign by Gollub et al. [17] in their study on scirrhous metastases to the gastrointestinal tract at CT. MRI also reveals the same findings and is as useful as CT. Other primaries, such as scirrhous carcinoma of the breast and bladder cancer, can also present with similar metastasis to the rectum and colon [17].

Endoscopic ultrasound (EUS) remains an indispensable modality of investigation in undiagnosed cases, as it can provide a circumferential view of the individual layers of the rectum and can detect intramural tumor infiltration even if the overlying mucosa appears normal. It can also aid in a deeper biopsy from representative layers in both the stomach and the rectum. In our case, repeated attempts at biopsy from the rectal stenosis were unsuccessful. This could be because the biopsy from colonoscopy could have been too superficial from the mucosa and the core needle biopsy might have traversed across the submucosa where the SRC are usually deposited. The peculiar histological pattern of metastasis in SRC carcinoma includes mucosal sparing, submucosal involvement, marked fibrosis within the bowel wall and sparseness of tumor cells in SRC carcinoma. Hence EUS-guided biopsy from the representative tissues (submucosa) might have been more successful in yield.

In addition to the well-established signs of inoperability for carcinoma stomach, such as Virchow’s node, Irish node, Blumer’s shelf, Sister Mary Joseph umbilical nodule, and Krukenberg’s tumor, SM could well be added to the list, as this is also considered a distant metastasis and R0 resection is impossible in such cases. Hence, only symptomatic palliation might be warranted in most cases. Palliative treatment can be addressed after confirming the diagnosis with a biopsy and then subjecting the patient either to a diversion sigmoid colostomy or a self-expanding metallic stent, followed by chemotherapy.

An entity to be ruled out before committing the patient to a treatment plan is the primary linitis plastica of the rectum. Its incidence is rarer than that of SM. All patients should undergo a mandatory OGD to search for a primary extra-rectal tumor, especially gastric because only its negativity confirms the primary lesion of the rectum. The prognosis of primary linitis plastica of the rectum is very dismal, averaging just a few months [18].

In conclusion, SM is an unusual mode of spread of cancer cells, seen in DGC, causing intestinal obstruction due to concentric rectal stenosis due to infiltration of SRC in the rectal submucosa. Awareness about this rare entity is needed for proper diagnosis and staging to avoid unnecessary major surgeries, as SM should be considered a sign of the advanced nature of the disease.