Introduction

The Roux-en-Y gastric bypass (RYGB) and one anastomosis gastric bypass (OAGB) are the two most commonly performed metabolic and bariatric surgical (MBS) procedures worldwide. In both of these techniques, the stomach is divided into a pouch and a remnant section [1,2,3,4]. Although upper endoscopy may visualize the gastric pouch, gastrojejunal anastomosis (GJA), and the non-diverted part of the small intestine, diagnosing and treating diseases in the gastric remnant are challenging and represent a significant limitation.

Problems of in situ remnant stomach may be categorized as perioperative and late complications [5,6,7]. Hemorrhage from sutures, staple lines or anastomosis, staple line dehiscence/leakage, and acute dilatation of gastric remnant are among the events that happen early in the postoperative course, and gastroduodenal bleeding/perforation, gastro-gastric fistula (GGF), late gastric remnant dilatation, and malignancy occur later [5,6,7,8]. Gastric remnant resection is one of the available approaches for overcoming these problems. Furthermore, it was hypothesized that gastric bypass with concomitant resection of the remnant stomach or the so-called resectional gastric bypass (RGB) might have an additional positive effect on weight loss and may perform as the primary bariatric approach for patients with severe obesity and in cases who are at high risk for developing problems in excluded remnant stomach such as malignancy or there is a fear of postoperative complications such as GGF, ulcer, bleeding, or perforation [5,6,7,8,9,10,11,12,13,14]. However, the reasons, outcomes, and complications of excising the remnant stomach in MBS candidate concomitant with their initial RYGB/OAGB or after a complication are not clear. Thus, in this systematic review, we aim to investigate the indications of remnant gastrectomy in addition to gastric bypass.

Methods and Materials

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) has been used to report the findings of this study [15], and the protocol of this review has been registered in the Prospective Register of Systematic Reviews (PROSPERO) database and received the code. This work has been reported in line with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) and AMSTAR [16] (Assessing the methodological quality of systematic reviews) Guidelines.

Search and Screening

PubMed, Scopus, Embase, Web of Science, and Cochrane were reviewed for articles published by the end of Dec 2020, and the search was updated twice in May and Dec 2023. The keywords searched were “remnant gastrectomy,” “resectional bypass,” “resectional gastric bypass,” “RGB,” “bariatric surgery,” “obesity surgery,” “weight loss,” “OAGB,” “MGB,” “MGB/OAGB,” “RYGB,” “Roux-en-Y gastric bypass,” “one anastomosis gastric bypass,” “mini gastric bypass,” or a combination of them in the title, abstract, or keywords. The included articles’ references and citations were manually reviewed for additional relevant papers. Duplication and conference presentations were removed, and the Covidence website was used to help two authors organize the screening process independently, and another author resolved the conflict. Authors of published congress presentations were contacted through email for their full-text articles. Non-English manuscripts were translated section by section using Google Translate. Inclusion criteria were all observational studies, including case reports, case series, and prospective and retrospective studies on total, subtotal, or partial remnant gastrectomy with or after gastric bypass procedures. Exclusion criteria were studies with wedge resection of the remnant stomach, fundectomy, unclear surgical procedures or results, and animal studies. Studies that have been conducted and published from the same center or might have investigated the same population are separated.

Data Extraction

The data of included studies (first author’s name, year of publication, design of study, sample size, age, gender, BMI before MBS, RYGB, or OAGB procedure for MBS, primary or secondary resectional gastric bypass, the type and reason of remnant gastrectomy, BMI at the time of remnant gastrectomy, time interval between MBS and remnant gastrectomy in case of secondary resectional gastric bypass, follow-up period after surgery, and BMI after remnant gastrectomy, any mentioned postoperative complications) extracted by the same two authors and checked by the other author. The difference observed in any step was resolved by another investigator independent of the other three. Primary remnant gastrectomy concomitant with the gastric bypass or RGB was defined when remnant gastrectomy was performed with a gastric bypass procedure (either RYGB or OAGB) and named secondary when a problem in the remnant stomach or a complication of RYGB/OAGB needed remnant gastrectomy as its treatment some months after the initial operation.

Results

A total of 66 studies examining 1918 patients were included in this study (Fig. 1); 20 studies reported simultaneous gastric bypass with remnant gastrectomy on 1751 patients, and 46 studies reported reoperation for remnant gastrectomy after gastric bypass in 167 patients. Characteristics of the included studies with their reported data are presented in Table 1 (simultaneous) and Table 2 (reoperation). Included patients aged 15–70 years, and the female gender was 70% of the included population.

Fig. 1
figure 1

PRISMA flow chart of the study

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Table 1 Characteristic of studies performed remnant gastrectomy simultaneous with the gastric bypass (resectional gastric bypass)
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Table 2 Characteristic of studies performed remnant gastrectomy after gastric bypass (reoperation or secondary resectional gastric bypass)
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Indications

Simultaneous

RGB was directly related to stomach neoplasia in 10 studies on 981 patients. Among them, four studies from areas with a high prevalence of stomach malignancy (South America, such as Chile, and East Asia, such as South Korea) performed remnant gastrectomy on 548 patients for preventive reasons, speculating that remnant stomach will become out-reached by routine upper endoscopy and postoperative surveillance is complicated in this situation. One study with 427 patients was about to find any incidental pathological findings in extracted specimens after MBS. The reported pathologic findings in gastric remnant were chronic or active gastritis in 66, fundic gland polyps in seven, intestinal metaplasia (IM) in three, gastric ulcer in two, lymphoid aggregate in two, diverticulum in one, a developmental cyst in one, and leiomyoma in one. Five case reports on six patients mentioned the reason for RGB was related to IM of the stomach in two patients, an incidental 4.5 cm exophytic gastrointestinal stromal tumor (GIST) on greater curvature, an 8 cm lymphoma, and two small duodenal neuroendocrine tumors.

Six studies with 607 patients performed RGB as the primary MBS approach to evaluate a new surgical technique for weight loss in patients with severe obesity and to overcome the potential problems of the in situ remnant stomach that may face afterward, including fistula, bleeding, ulcer, and neoplasia. RGB was used as a revisional option after a failed prior MBS approach (i.e., having weight problems or intractable symptoms after restrictive approaches) for 86 patients of three articles. GERD was mentioned in two studies with 75 patients, which used RGB for treating both severe obesity and preoperative GERD with IM of the esophagus (i.e., Barret's esophagus, BE). Finally, one reported case with GI bleeding due to Lynch syndrome and gastric polyp and another due to significant stomach distortion because of the previous band erosion and insufficient blood supply to the remnant stomach needed RGB for definite treatment.

Reoperation

The mean interval between the initial MBS procedure and remnant gastrectomy in the reoperation group was 77 months (with a median of 43 months). Remnant gastrectomy after primary gastric bypass was performed for these causes from the highest to lowest reported rate among the included studies: GGF was the main initial reason for remnant gastrectomy from 11 studies with 93 patients (56%). A mean interval of 32 months (with a median of 23 months) was observed between gastric bypass and remnant gastrectomy for GGF. Insufficient weight loss/weight regain (IWL/WR), bleeding, marginal ulcer (MU), GJA problems, or being significantly and continuously symptomatic (pain and vomiting) were accompanying problems of the GGF that made surgeons reoperate the patients. Retrograde bile reflux to the remnant stomach and symptomatic gastritis was reported by one study with 19 patients to be the reason for their remnant gastrectomy after RYGB. There were 13 studies with 19 patients who developed neoplasia after gastric bypass. Gastric adenocarcinoma with 11 patients was the most reported, GIST with three, and lymphoma with one was the other. There is one study reporting four cases with pancreaticoduodenal cancers (one patient for each of islet cell, acinar, and adenocarcinoma of pancreas and one duodenal ampullary malignancy) treated with remnant gastrectomy ± Whipple procedure. The reason for the remnant gastrectomy was massive, intractable bleeding in 11 studies with 14 cases. The source of bleeding was from gastric ulcer in the six studies with nine patients, duodenal ulcer in two, one due to MU, one from GGF without any other pathology neither in pouch nor in remnant, and one from polypoid mass, which was later found to be due to the Cronkhite-Canada syndrome. MU was the reason for remnant gastrectomy in two studies with 13 patients; nine of them had concomitant GGF, and one of them was refractory to both medical and surgical treatments and remnant gastrectomy was inevitable. Peritonitis due to perforation of the remnant stomach and proceeding gastrectomy were reported in nine patients of eight studies. The reasons for perforation were related to peptic ulcer diseases (PUD) in two patients, proximity of remnant stomach to MU after OAGB and gastric lymphoma each in one patient, and necrosis mostly related to ischemic dilatation due to increased intraluminal pressure-induced by Peterson’s internal hernia, jejunojejunal anastomosis stricture, gastric outlet obstruction by blood clot, or being unknown and justified by the previous manipulation on normal anatomy of vessels, embolic events, or hypercoagulable state. Finally, one report found gastroduodenal intussusception of gastric remnants after OAGB.

Outcomes and Complications

Pooled data of reported BMI 6 months and 1 year after RGB had a range of 27.54–33.2 kg/m2 and 24.69–28.5 kg/m2, respectively, and for %EWL at 6-month and 1-year follow-up, they reported 46–59.8% and 71–97%, respectively.

Regardless of death due to cancers, four deaths were reported with causes related to infection/sepsis/organ failure in three and pulmonary thromboembolism in one patient. The detected source of infection was an anastomotic leak and pneumonia in each patient. The remaining one had prolonged hyperthermia and cardiovascular failure after that. The rates of other reported complications are in Table 3.

Table 3 Reported complications after resectional gastric bypass (both primary and secondary)
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Discussion

There are many reasons through the literature that made surgeons remove the stomach concomitant with the RYGB/OAGB (either as primary MBS to the GI anatomy or revision to another approach) or after a period from the original procedure due to the occurrence of a problem.

Indications

Simultaneous

Malignancy

The risk of neoplasia was the main reason for resecting the remnant stomach concomitant with a standard RYGB/OAGB. RGB had been performed for preventive causes when surgeons were highly suspicious of developing gastric cancer in the future, mostly for patients living in areas with a high prevalence of gastric cancer, such as in East Asia (South Korea) and Central and South America (Chile) [6, 9, 11, 12, 22] and curiosity on what may have found on specimens extracting from 427 patients [24]. However, there is no strong evidence that MBS, mostly gastric bypass, increases the risk of future gastric cancers in predisposed patients, such as those living in areas with a high prevalence [6, 10,11,12, 22], positive family history, or a high-risk pathology that may advance to malignancy (e.g., IM, dysplasia, adenomatous polyps, and Menetrier’s disease) [44]; the remanent stomach is going to be out-reached by standard upper endoscopy after surgery, and therefore, it is better to exclude this part from the system [6, 7, 10,11,12, 22]. Although these investigations advocated their hypothesis without increased burden, acceptable weight loss, and similar predictable postoperative complications in comparison to SG/RYGB (except for a significant change in serum level of vitamin B12) [9], other surgeons did not dare to pose such an unknown high-risk procedure to their patient in other parts of the world. Regardless of omitting the remnant stomach from the system, there is still a risk of malignancy in the gastric pouch or at the GJA. However, these parts are easily accessible through upper endoscopy. The remaining uninvestigated point is the risk of malignancy after RGB and its comparison to RYGB to evaluate whether RGB prevents cancer much more than RYGB.

Another aspect of this problem is that obesity and gastritis with mucosal atrophy due to chronic inflammation by Helicobacter pylori (HP) or autoimmune condition are among the risk factors for developing pathologic changes that transform the normal gastric histology to the IM. Without proper treatment, IM may progress to dysplasia and, eventually, the most common type of gastric malignancy, adenocarcinoma. IM was reported to be the main intention of RGB in 2 patients of 2 included articles and was incidentally found in only three specimens of Sohn et al. and 8.9–10.5% of Braghetto et al. evaluations [11, 12, 17, 18, 21, 24, 26]; definite gastric cancer was not found in any of the previous investigations. Similar to patients who are categorized as high-risk for developing gastric cancer in the future, with gastric bypass, most of the stomach is not easily accessible by upper endoscopy. Therefore, remnant gastrectomy is a reasonable option in these cases for both therapeutic and preventive intentions [6, 22]. Gastritis (either acute, chronic, atrophic, or lymphoid), gastric polyps, and ulcers are other reported pathologies in the remnant stomach that were found incidentally in Sohn et al. and Braghetto et al. histologic reports of the extracted stomach and may have been found in populations with severe obesity similar to normal populations [11, 24]. Gastritis or gastric ulcers regress significantly with effective acid-reducing agents such as PPI. However, unless there is IM, dysplasia, or early stages of adenocarcinoma in taken biopsies, there is no need to perform RGB to prevent gastric adenocarcinoma. There are several types of gastric polyps, and unless they are symptomatic (e.g., severe abdominal pain, bleeding, perforation), large enough, or at high risk of transforming into cancerous lesions (e.g., in hyperplastic and adenomatous types), excision is not indicated.

Incidental findings of GIST, neuroendocrine tumor in the duodenum, and lymphoma were other reasons for RGB in relation to neoplasia. GISTs with local restriction to stomach larger than 2 cm (and in some cases > 1 cm due to the risk of metastasis) or symptomatic types (i.e., with mass effect or mucosal ulcer) are removed surgically [75] with adequate margin. If anatomically applicable, for a patient with GIST and severe obesity, sleeve gastrectomy (SG) is an excellent option to capture the tumor along with the resected stomach in case of no contraindications of SG [19, 75, 76]. Otherwise, RYGB with wedge resection of the tumor is recommended [76]; remnant gastrectomy is for when we cannot have a negative microscopic margin with standard RYGB + wedge resection of the tumor [19, 75, 76], or it is surgically challenging for the surgeon and performing an RGB is more accessible with lower risk. Duodenal neuroendocrine tumor and gastric lymphoma were reported in two case reports, and we think the same surgical principle applies to these tumors as well. However, the role of preoperative upper endoscopy in inspecting gastric mucosa shines in this scenario [19, 25, 75, 76]. Indeed, in the report by Quesada et al., lymphoma was not identified in the preoperative upper endoscopy and was then found during the surgery by full visualization of the stomach from an external view. The same experience was reported in many GIST cases, especially when the tumor was growing away from the gastric mucosa (exophytic), necessitating surgeons to inspect the stomach externally during the operation before firing the staples [19, 25, 75, 76].

Avoiding Future Remnant Problems and Weight Troubles

Failure of previous approach based on weight (IWL/WR) mostly after restrictive approaches (e.g., vertical banded gastroplasty, SG, gastric banding, and horizontal banded gastroplasty) was one of the main reasons for RGB in Curry, Martin, and Noun et al. studies [5, 7, 29]. Although RGB is not a common decision for conversion after a variety of failed primary MBS [77], their comparison with primary RGB or SG [5, 7, 9] supports this idea that besides some predictable challenges, RGB is reliable, safe, and applicable after failed primary MBS or even in a special situation as the main gastric bypass approach to eliminate both severe obesity and the future development of potential complications in the remnant stomach (e.g., fistula, ulcer, gastric dilatation, staple line disruption, hemorrhage, or late malignancy) or to resolve a symptomatic problem of restrictive MBS approach (e.g., dysphagia) [5,6,7, 11, 14, 26,27,28] with comparable weight loss not more than what is expected and with the same profile of complications as the standard RYGB has [5, 7, 9, 11, 14, 26,27,28].

GERD

Csendes et al., on 15 patients with BE, revealed that RGB is an excellent anti-reflux procedure for patients with severe obesity and BE + IM of the cardia [13]. However, the need for more evidence on this subject made Braghetto et al. conduct a three-arm study [12]. They implied RGB is the choice for patients with severe obesity and preoperative GERD + BE without the need for fundoplication in comparison to the other two approaches, in which one of them had fundoplication, vagotomy, distal gastrectomy + RY gastrojejunostomy (FVDGRYGJ, removing 60% of the stomach vs. 95% in RGB). The prior method had the exact resolution of GERD + BE but with lower weight loss and different postoperative complication profiles not discussed by the authors [12]. The observed difference in weight loss could be justified by the amount of resected stomach and their difference in choosing the alimentary RY limb (130–150 cm in RGB vs. 60–70 cm in the other). Regarding their postoperative complications, dysphagia in the FVDGRYGJ group could relate to fundoplication, and diarrhea/dumping may be explained by the size of the gastric pouch and limb length discrepancies.

Reoperation

Remnant gastrectomy in previously bypassed patients was mainly indicated to treat a postoperative complication either directly or indirectly associated with the gastric bypass procedure. GGF, GERD, MU, neoplasia, bleeding, and perforation are among the highest reported indications of secondary RGB and other rare causes limited to case reports such as necrosis and intussusception of the remnant stomach to duodenum after OAGB.

GGF

The pathway between the gastric pouch and remnant, called GGF, may develop due to various initiators, mainly leak and inflammation from the staple line, and may complicate 1–6% of the cases after RYGB [36, 55]. GGF with the presenting symptom of abdominal pain or vomiting may be the sole problem [74] or be associated with MU, as reported in a different study found together in 16–75% of the cases and other accompanying problems such as bleeding from the fistula [65] or ulcer [34, 57], food intolerance [74], perforation/peritonitis, GJA stenosis [74], or IWL/WR [10, 36, 50, 60, 74]. At first, for small GGF, conservative management constituting PPI, sucralfate, HP eradication if positive, and cessation of NSAIDs and smoking are recommended [10, 59, 74]. In the next step, multiple endoscopic attempts (e.g., glue, clip, or stent placement) may be tested because they are safe, non-invasive, and buy some time to decide what to do next as Campos et al. and other surgeons have recommended [50, 54]. However, they are unacceptable for large tracts due to the high failure rate [36]. Therefore, surgical intervention is the most definite option when the patient is unresponsive to medical/endoscopic treatments with intractable symptoms [10, 50, 59, 74, 78]. GGF surgical intervention has been mentioned to have two types based on the distance between GJA and opening of GGF into the gastric pouch [36], patient symptoms or accompanied problem (e.g., bleeding, MU, or WR) [34, 57, 65], and surgeon preference such as a compromised optimal surgical view by the local inflammation and adhesions [10, 36, 50, 54, 55, 58, 74]. Fistula tract resection with perseveration of GJA by resecting a part of the gastric pouch and remnant stomach or en bloc resection of GGF and GJA with re-do of the GJA are the two proposed methods [10, 36]. Although the amount of remnant resection is different between studies and depends on various factors, it seems the earlier approach with remnant gastrectomy in which a part or nearly all of the source of acid production is deleted is more favorable [10, 54, 57, 59, 74] due to fear of future development of MU, GGF recurrence, and some severe complications [58, 60] unless recreation of the gastric pouch and revision of the GJA is needed such as in enlarged pouch, stenosis of the GJA, and intractable MU or its associated problems [57, 58, 60]. The interruption in weight loss or WR after surgery is due to the dual route of food pathway and impaired balance between gut hormones, all reversible after GGF repair and restoring the body to what it was after bypass surgery [61]. The bleeding and MU are associated with long-term exposure of gastric pouch and GJA to the acid produced in the remnant stomach brought by GGF and the presence of the remnant stomach itself having G-cells, the origin of gastrin, which stimulates acid production by parietal cells. Therefore, GGF repair with remnant gastrectomy diminishes the main source of acid production and relieves the MU and bleeding [34, 57].

Bile Reflux Gastritis

Bile reflux is not a severe concern after OAGB [79]. However, intractable abdominal pain due to bile reflux gastritis of the remnant stomach is a rare complication not have been evaluated thoroughly. La Vella et al. [49] study estimated this problem to be near 2.7%. Although all of their patients were under PPIs, they performed remnant gastrectomy without testing other potential medical treatments such as ursodeoxycholic acid or prokinetics. Therefore, RGB for this scenario needs justification and further investigation.

Neoplasia

There are few gastric and pancreaticoduodenal neoplasms after gastric bypass [48, 62]. Gastric cancers were adenocarcinoma [11, 47, 70,71,72,73], GIST [42, 62, 63], and lymphoma [43]; adenocarcinoma was reported the most [11, 47, 62, 70,71,72,73]. Patients of this group were diagnosed due to the appearance of symptoms such as abdominal pain, dysphagia, vomiting, bleeding, iron deficiency anemia, further weight loss after plateau, or they may remain asymptomatic for an extended period [42, 48] and stay undiagnosed till some severe symptoms appear (e.g., perforation or obstruction) [43]. On the other hand, negligence of symptoms and misinterpretation of common post-bariatric problems and being out-reach by the standard evaluations made these tumors diagnosed at more advanced stages [42,43,44, 47, 70,71,72,73]. Although there is speculation that the incidence of GIST is higher in the bariatric population than in ordinary people [75], lymphoma does not seem to have a direct strong association with obesity [43]. Indeed, HP and chronic mucosal inflammation due to duodenal reflux after gastric bypass may have a role in lymphocyte infiltration and, therefore, gastric stump and distal gastric lymphoma development [43]. However, obesity has an association with IM and gastric adenocarcinoma as it is an independent factor [44].

Instead, although there are large studies indicating cancer development decrease in the MBS group [62] and there is a long period between surgery and detecting cancer, indicating a low probability of a direct causal relationship [46, 70], whether the incidence of IM and gastric cancer will increase by MBS especially after gastric bypass is a debated area. Regardless of the HP, the excluded part does not have close contact with carcinogenic materials in food; however, it has continuous exposure to an acidic environment without food and sometimes duodenopancreaticobiliary contents (i.e., bile reflux), which has shown to be carcinogenic for stomach [44, 45]. Inevitably, remnant gastrectomy is the treatment of choice for gastric adenocarcinoma, GIST, and lymphoma in the excluded stomach [42, 43, 47, 62, 63, 71,72,73]; indeed, it has a preventive aim for IM to cease its progression to dysplasia.

Bleeding

Another rare but life-threatening challenge after gastric bypass is gastrointestinal bleeding with an incidence rate of less than 1% to nearly 5% [30], which, after complete evaluations, may turn out to be from the remnant stomach and its proceeding part, duodenum [39, 41, 67]. PUD with a spectrum of pathologic changes in the stomach (i.e., gastritis and gastric ulcer) or duodenum due to NSAID consumption, HP infection, or unknown causes were the source of bleeding in most cases [30, 32, 37, 39, 40, 52, 64, 67]. Furthermore, bleeding could be associated with mass [20, 38], GGF [65], MU [34], or even some rare cases such as erosion of gastric remnant fundus with the diaphragmatic vessel [76], splenic pseudoaneurysm [37], or perforation/peritonitis [31, 40]. Upper endoscopy is recommended as the first diagnostic approach [30]. However, push or double-balloon enteroscopy is the final preferred approach to inspect the duodenum and remnant stomach after being unremarkable. Bleeding due to PUD is reasonably managed with blood transfusion if indicated, high doses of PPI, antibiotics for HP eradication if positive, and cessation of NSAIDs consumption and smoking [67], which are also the routine first-line treatments for MU and GGF [34]. Although most surgeons advise stepwise management [64] and the nonoperative approach was successful in some cases [80], being resistant to medical and endoscopic treatments (such as electrocautery and clip), recurrence, perforation, producing instability of hemodynamics, or having accompanying problems such as malignancy, MU, or GGF, made surgeon remove the remaining part of the stomach for definite treatment and patient survival [30, 32, 34, 37, 39, 40, 52, 65, 80].

Peritonitis

Peritonitis due to perforation was only reported in a few case reports. It was related to (1) NSAIDs or HP-induced PUD, (2) MU, (3) ischemia and necrosis of remnant stomach induced by increased intra-luminal pressure due to jejunojejunal anastomotic stricture, small bowel obstruction because of internal hernia, remnant outlet obstruction by accumulation of blood clots due to bleeding or cancer, and (3) unknown in some situations [33, 35, 37, 40, 66,67,68,69, 80]. Before reaching the acute abdomen, most patients may have had other symptoms (abdominal pain ± tenderness, dizziness, lightheadedness, fatigue, dyspnea), but ignorance or underestimation by both surgeon and patient may lead to perforation [31]. Abdominal pain is the presenting symptom with the highest prevalence, which could be misdiagnosed and misinterpreted as one of the common problems after MBS. Regardless of asymptomatic scenarios, surgeons should alert their patients regarding these gastrointestinal symptoms and encourage them to seek medical professionals. Surgeons should comprehensively investigate patients presenting with these symptoms to roll out serious causes. Finally, a high suspicion level is required to detect these diseases at the beginning of their development. However, general postoperative recommendations such as avoiding smoking and chronic use of NSAIDs and empirical PPI after complete evaluations could be a reasonable approach for most patients to prevent the development of ulcers or slow their progression. Ulcer-induced perforations may be treated with patch-repair [35]; however, remnant gastrectomy was performed for cases with failure or medical/endoscopic treatments, diminished optimal view for other procedures [68], instability of hemodynamics [31], and irreversible ischemia/necrosis of a substantial segment of the remnant stomach [33, 40].

MU

The pathophysiology of MU after gastric bypass is unclear; the proximity of gastric tissue to the intestinal mucosa and the disruption of the mucosal protection mechanism could explain it. MU may occur as a sole problem after surgery, presenting with abdominal pain, or be associated with GGF [34, 57, 58]. Symptoms of MU have a wide range and could cause GJA stricture and obstruction, bleeding, and perforation [34, 68]. As long as MU is highly related to an acidic environment without proper mucosal protection, medical treatment tries to address these points [51]. However, in case of persistence, bleeding, stricture, or perforation, a revision to the GJA and en bloc resection of the affected area with a new pouch creation is the recommended surgical approach [34, 57]. Remnant gastrectomy has been mostly performed for cases with additional problems of MU, such as GGF [10, 57, 58] or unresponsiveness to prior medical and surgical management [34, 57, 68]. Indeed rare, two cases had their remnant stomach removed due to intractable MU, one with resistance to all of the medical and surgical actions [51] and the other had a perforation of the remnant stomach due to proximity to ulcer and inflamed area [68]. Most studies did not report the number and reason behind remnant gastrectomy of MU with vs. without accompanying problems such as GGF, which needs further investigation.

Outcomes and Complications

In contrast to indications of RGB, data regarding the postoperative complications and outcomes of RGB and its comparison to SG and standard RYGB/OAGB is scarce; one explanation is that simultaneous remnant gastrectomy with gastric bypass is not a standard procedure and few surgeons have to perform it for mostly preventive intentions and to evaluate whether this approach would help their patients. On the other hand, remnant gastrectomy after gastric bypass had to be performed for the final treatment of some complications. Previous investigations advocate that remnant gastrectomy with or after gastric bypass does not affect the amount of weight loss compared to standard RYGB or SG [9]. It indicates that weight loss after RYGB or RGB is related to the size of the gastric pouch, length of limbs, and patient adherence to postoperative recommendations regarding eating habits and exercise [5,6,7, 9, 11, 12, 22]. The pooled postoperative data of %EWL or ΔBMI indicates that they are within the expected range at 6 and 12 months after either primary or secondary RGB [5, 6, 12, 22]. Indeed, it facilitates weight loss in those who had failed prior operations or WR due to problems such as GGF [5, 9, 29, 36, 50, 60, 61]. Previously known concerns about standard RYGB apply too after RGB but with permanent elimination of the potential risks that may occur after primary gastric bypass relating to the remnant stomach, such as staple line disruption or enlargement of the residual stomach, and eventual future development of remnant gastric neoplasia or its potential for acid production as in MU, GGF, and bleeding. Post-gastric bypass problems, which led the surgeons to perform a reoperation and conduct remnant gastrectomy, had a 100% success rate without direct mortality, and none of the problems recurred after secondary RGB. Regardless of the surgical challenge, longer operation time, more intraoperative bleeding, and risks of iatrogenic injuries to the vessels (e.g., hemoperitoneum, hepatic and phrenic veins, and short gastric artery) and organs (e.g., spleen and small bowel), RGB is different from standard RYGB in terms of necessitating an experienced surgical team in gastrectomy. Despite their rarity, duodenal stump leak, stricture, hemorrhage from different sites, leak from anastomosis, collection (e.g., in subphrenic or subhepatic regions), intra-abdominal abscess, occasional nausea, post-prandial pain or diarrhea/dumping syndrome, ventral hernia (mainly after open surgery), obstruction (either due to internal hernia or adhesion bands), and wound problems (e.g., seroma, superficial infection, dehiscence, and necrosis mainly after open operations) are some of the reported complications after RGB, which were predictable similar to any other operation [11, 12, 21, 22, 49, 57]. Other postoperative complications (e.g., Clostridium difficile colitis, perioperative myocardial infarction, urinary tract infection/retention, ileus, thrombosis, atelectasis, and pneumonia) are a risk of any significant procedure and seem they have no association with remnant gastrectomy. However, iron deficiency anemia and vitamin B12 deficiency are predictable after remnant gastrectomy due to the elimination of acid and intrinsic factor secretion from parietal cells [10, 22, 57]. However, both of these conditions are rare; our body has a large reserve of them, and they can easily be diagnosed with a complete blood count test and will be managed with iron and B12 supplements (either oral or parental) [10, 22, 57]. The comparison of RGB vs. SG in the Cho et al. study only revealed lower levels of vitamin B12 and, therefore, a higher supplementation rate [9]. Finally, RGB is a permanent act, omitting the chance to reverse the operation [81]; although uncommon, it may be used for cases with severe malnutrition, such as low albumin level, BMI < 18 kg/m2, or acute liver failure [81].

Conclusion

Remnant gastrectomy concomitant with gastric bypass has been mostly performed in areas with a high prevalence of gastric cancer because of being out-reach by upper endoscopy and hard to detect; therefore, it is better to eliminate the risk. Regardless of the gastric cancer, failure of other approaches, occurrence of post-bariatric intractable symptoms, GERD, and avoiding problems that may occur due to in-site remnant stomach mainly relating to its potential for acid production such as fistula, ulcer, gastric dilatation, staple line disruption, or hemorrhage were other reasons that made surgeon to perform the RGB for patients with severe obesity. Remnant gastrectomy after gastric bypass was performed to treat post-bariatric complications such as fistula, MU, bleeding, peritonitis, and neoplasia with a near 100% resolution rate and no recurrence. Rather than some unique complications relating to remnant gastrectomy, such as duodenal stump leak and anemia (either due to iron deficiency or vitamin B12), RGB has the same range of weight reduction in comparison to standard RYGB or SG; indeed, it helps lose weight in those who had IWL/WR or diminish intractable symptoms due to failed prior procedures.