CT in the clinical and prognostic evaluation of acute graft-vs-host disease of the gastrointestinal tract

Diagnostic prediction of gastrointestinal graft-versus-host disease based on a clinical- CT- signs nomogram model

OBJECTIVE

Gastrointestinal graft-versus-host disease (GI-GVHD) is one of the complications that can easily occur after hematopoietic stem cell transplantation (HSCT). Timely diagnosis and treatment are pivotal factors that greatly influence the prognosis of patients. However, the current diagnostic method lacks adequate non-invasive diagnostic tools.

METHODS

A total of 190 patients who suspected GI-GVHD were retrospectively included and divided into training set (n = 114) and testing set (n = 76) according to their discharge time. Least absolute shrinkage and selection operator (LASSO) regression was used to screen for clinically independent predictors. Based on the logistic regression results, both computed tomography (CT) signs and clinically independent predictors were integrated in order to build the nomogram, while the testing set was verified independently. The receiver operating characteristic (ROC), area under the curve (AUC), decision curve, and clinical impact curve were used to measure the accuracy of prediction, clinical net benefit, and consistency of diagnostic factors.

RESULTS

Four key factors, including II-IV acute graft-versus-host disease (aGVHD), the circular target sign, multifocal intestinal inflammation, and an increased in total bilirubin, were identified. The combined model, which was constructed from CT signs and clinical factors, showed higher predictive performances. The AUC, sensitivity, and specificity of the training set were 0.867, 0.787, and 0.811, respectively. Decision curve analysis (DCA), net reclassification improvement (NRI), and integrated discrimination improvement (IDI) showed that the developed model exhibited a better prediction accuracy than the others.

CONCLUSIONS

This combined model facilitates timely diagnosis and treatment and subsequently improves survival and overall outcomes in patients with GI-GVHD.

CRITICAL RELEVANCE STATEMENT

GI-GVHD is one of the complications that can easily occur after HSCT. However, the current diagnostic approach lacks adequate non-invasive diagnostic methods. This non-invasive combined model facilitates timely treatment and subsequently improves patients with GI-GVHD survival and overall outcomes.

KEY POINTS

• There is currently lacking of non-invasive diagnostic methods for GI-GVHD. • Four clinical CT signs are the independent predictors for GI-GVHD. • Association between the CT signs with clinical factors may improve the diagnostic performance of GI-GVHD.

Effect of GVHD on the gut and intestinal microflora

Graft-versus-host disease (GVHD) is one of the most important cause of death in patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). The gastrointestinal tract is one of the most common sites affected by GVHD. However, there is no gold standard clinical practice for diagnosing gastrointestinal GVHD (GI-GVHD), and it is mainly diagnosed by the patient's clinical symptoms and related histological changes. Additionally, GI-GVHD causes intestinal immune system disorders, damages intestinal epithelial tissue such as intestinal epithelial cells((IEC), goblet, Paneth, and intestinal stem cells, and disrupts the intestinal epithelium's physical and chemical mucosal barriers. The use of antibiotics and diet alterations significantly reduces intestinal microbial diversity, further reducing bacterial metabolites such as short-chain fatty acids and indole, aggravating infection, and GI-GVHD. gut microbe diversity can be restored by fecal microbiota transplantation (FMT) to treat refractory GI-GVHD. This review article focuses on the clinical diagnosis of GI-GVHD and the effect of GVHD on intestinal flora and its metabolites.

Multi-parametric MRI in the diagnosis and scoring of gastrointestinal acute graft-versus-host disease

OBJECTIVES

Acute gastrointestinal graft-versus-host disease (GI-aGVHD) is a severe complication of allogeneic hematopoietic stem cell transplantation (HSCT). Diagnosis relies on clinical, endoscopic, and pathological investigations. Our purpose is to assess the value of magnetic resonance imaging (MRI) in the diagnosis, staging, and prediction of GI-aGVHD-related mortality.

METHODS

Twenty-one hematological patients who underwent MRI for clinical suspicion of acute GI-GVHD were retrospectively selected. Three independent radiologists, blinded to the clinical findings, reanalyzed MRI images. The GI tract was evaluated from stomach to rectum by analyzing fifteen MRI signs suggestive of intestinal and peritoneal inflammation. All selected patients underwent colonoscopy with biopsies. Disease severity was determined on the basis of clinical criteria, identifying 4 stages of increasing severity. Disease-related mortality was also assessed.

RESULTS

The diagnosis of GI-aGVHD was histologically confirmed with biopsy in 13 patients (61.9%). Using 6 major signs (diagnostic score), MRI showed 84.6% sensitivity and 100% specificity in identifying GI-aGVHD (AUC = 0.962; 95% confidence interval 0.891-1). The proximal, middle, and distal ileum were the segments most frequently affected by the disease (84.6%). Using all 15 signs of inflammation (severity score), MRI showed 100% sensitivity and 90% specificity for 1-month related mortality. No correlation with the clinical score was found.

CONCLUSION

MRI has proved to be an effective tool for diagnosing and scoring GI-aGVHD, with a high prognostic value. If larger studies will confirm these results, MRI could partly replace endoscopy, thus becoming the primary diagnostic tool for GI-aGVHD, being more complete, less invasive, and more easily repeatable.

KEY POINTS

• We have developed a new promising MRI diagnostic score for GI-aGVHD with a sensitivity of 84.6% and specificity of 100%; results are to be confirmed by larger multicentric studies. • This MRI diagnostic score is based on the six MRI signs most frequently associated with GI-aGVHD: small-bowel inflammatory involvement, bowel wall stratification on T2-w images, wall stratification on post-contrast T1-w images, ascites, and edema of retroperitoneal fat and declivous soft tissues. • A broader MRI severity score based on 15 MRI signs showed no correlation with clinical staging but high prognostic value (100% sensitivity, 90% specificity for 1-month related mortality); these results also need to be confirmed by larger studies.

PET assessment of acute gastrointestinal graft versus host disease

Acute gastrointestinal graft versus host disease (GI-GVHD) is a common complication following allogeneic haematopoietic cell transplantation (HCT), and is characterised by severe morbidity, frequent treatment-refractoriness, and high mortality. Early, accurate identification of GI-GVHD could allow for therapeutic interventions to ameliorate its severity, improve response rates and survival; however, standard endoscopic biopsy is inadequately informative in terms of diagnostic sensitivity or outcome prediction. In an era where rapid technological and laboratory advances have dramatically expanded our understanding of GI-GVHD biology and potential therapeutic targets, there is substantial scope for novel investigations that can precisely guide GI-GVHD management. In particular, the combination of tissue-based biomarker assessment (plasma cytokines, faecal microbiome) and molecular imaging by positron emission tomography (PET) offers the potential for non-invasive, real-time in vivo assessment of donor:recipient immune activity within the GI tract for GI-GVHD prediction or diagnosis. In this article, we review the evidence regarding GI-GVHD diagnosis, and examine the potential roles and translational opportunities posed by these novel diagnostic tools, with a focus on the evolving role of PET.

Intestinal and Multivisceral Transplantation: Complications

Advancements in immunosuppression protocols, surgical techniques, and postoperative care in the last few decades have improved outcomes of intestinal transplant patients. Normal immediate postoperative imaging appearance can simulate pathology. Intestinal transplant recipients are prone for several postoperative complications due to the complex surgical technique, which involves multiple anastomoses, and immunogenic nature of the allograft intestine. Imaging plays a crucial role in detection of several major complications including infectious, immunologic, vascular, gastrointestinal, pancreaticobiliary, genitourinary, and neoplastic complications. The awareness of the posttransplant anatomy and normal imaging appearances helps radiologists anticipate and accurately detect posttransplant complications.

Advances in Imaging of Inflammation, Fibrosis, and Cancer in the Gastrointestinal Tract

Gastrointestinal disease is prevalent and broad, manifesting itself in a variety of ways, including inflammation, fibrosis, infection, and cancer. However, historically, diagnostic technologies have exhibited limitations, especially with regard to diagnostic uncertainty. Despite development of newly emerging technologies such as optoacoustic imaging, many recent advancements have focused on improving upon pre-existing modalities such as ultrasound, computed tomography, magnetic resonance imaging, and endoscopy. These advancements include utilization of machine learning models, biomarkers, new technological applications such as diffusion weighted imaging, and new techniques such as transrectal ultrasound. This review discusses assessment of disease processes using imaging strategies for the detection and monitoring of inflammation, fibrosis, and cancer in the context of gastrointestinal disease. Specifically, we include ulcerative colitis, Crohn's disease, diverticulitis, celiac disease, graft vs. host disease, intestinal fibrosis, colorectal stricture, gastric cancer, and colorectal cancer. We address some of the most recent and promising advancements for improvement of gastrointestinal imaging, including unique discussions of such advancements with regard to imaging of fibrosis and differentiation between similar disease processes.

Gastrointestinal bleeding: imaging and interventions in cancer patients

Gastrointestinal bleeding (GIB) among cancer patients is a major source of morbidity and mortality. Although a wide variety of etiologies contribute to GIB, special considerations should be made for cancer-related factors such as the type of malignancy, location and extent of disease, hemostatic parameters, and treatment effects. Key imaging modalities used to evaluate GIB include computed tomography angiography (CTA), radionuclide imaging, and catheter-based angiography. Understanding the cancer and treatment history and recognizing the associated imaging manifestations are important for identifying the source and potential causes of GIB in cancer patients. This article will review the common clinical presentations, causes, imaging manifestations, and angiographic management of GIB in cancer patients.

Gastrointestinal Manifestations of Immunodeficiency: Imaging Spectrum

There is a wide spectrum of hereditary and acquired immunodeficiency disorders that are characterized by specific abnormalities involving a plethora of humoral, cellular, and phagocytic immunologic pathways. These include distinctive primary immunodeficiency syndromes due to characteristic genetic defects and secondary immunodeficiency syndromes, such as AIDS from HIV infection and therapy-related immunosuppression in patients with cancers or a solid organ or stem cell transplant. The gut mucosa and gut-associated lymphoid tissue (the largest lymphoid organ in the body), along with diverse commensal microbiota, play complex and critical roles in development and modulation of the immune system. Thus, myriad gastrointestinal (GI) symptoms are common in immunocompromised patients and may be due to inflammatory conditions (graft versus host disease, neutropenic enterocolitis, or HIV-related proctocolitis), opportunistic infections (viral, bacterial, fungal, or protozoal), or malignancies (Kaposi sarcoma, lymphoma, posttransplant lymphoproliferative disorder, or anal cancer). GI tract involvement in immunodeficient patients contributes to significant morbidity and mortality. Along with endoscopy and histopathologic evaluation, imaging plays an integral role in detection, localization, characterization, and distinction of GI tract manifestations of various immunodeficiency syndromes and their complications. Select disorders demonstrate characteristic findings at fluoroscopy, CT, US, and MRI that permit timely and accurate diagnosis. While neutropenic enterocolitis affects the terminal ileum and right colon and occurs in patients receiving chemotherapy for hematologic malignancies, Kaposi sarcoma commonly manifests as bull's-eye lesions in the stomach and duodenum. Imaging is invaluable in treatment follow-up and long-term surveillance as well. Online supplemental material is available for this article. ^©RSNA, 2022.

Fluorodeoxyglucose F 18 for the Assessment of Acute Intestinal Graft-versus-Host Disease and Prediction of Response to Immunosuppressive Therapy

Graft-versus-host disease (GVHD) is a common complication that increases morbidity and mortality after allogeneic stem cell transplantation (allo-SCT). Fluorodeoxyglucose F 18 (¹⁸F-FDG)-positron emission tomography (PET) imaging has been demonstrated to be highly informative for evaluating and mapping of intestinal GVHD. To corroborate and extend existing findings and to investigate whether glucose metabolism assessed by ¹⁸F-FDG-PET might be an effective diagnostic tool to predict corticosteroid-refractory acute GVHD and overall survival. In this retrospective analysis, 101 patients with clinically suspected acute intestinal GVHD underwent ¹⁸F-FDG-PET between June 2011 and February 2019. Seventy-four of these patients with clinically and/or histologically proven acute intestinal GVHD as well as positive ¹⁸F-FDG-PET findings were analyzed in detail to assess the predictive value of ¹⁸F-FDG-PET regarding the response to immunosuppressive therapy and survival. Quantitative PET parameters, particularly the maximum standard uptake value (SUVmax), of patients with a fast response (ie, clinical improvement and decreased GVHD activity by at least 1 stage after 1 week of GVHD treatment) or slow/no response (ie, persistent disease activity for more than 1 week or increasing GVHD activity following first-line immunosuppressive therapy) were evaluated. ¹⁸F-FDG-PET detected intestinal GVHD with a sensitivity of 93% (95% confidence interval [CI], 85% to 97%) and specificity of 73% (95% CI, 45% to 91%). Patients with a fast response to immunosuppressive therapy had a mean SUVmax of 13.7 (95% CI, 11.0 to 16.5) compared with 7.6 (95% CI, 7.0 to 8.3; P = .005) observed in patients with prolonged or no response. The median overall survival (OS) was 573.0 days (95% CI, 539.5 to 606.5 days) for patients with fast response versus 255 days (95% CI, 161.0 to 349.0 days; P = .009) for patients with slow or no responses. A SUVmax threshold >8.95 applied to ¹⁸F-FDG-PET performed within 100 days after transplantation identified patients with a median OS of 390 versus 117 days for patients with SUVmax ≤8.95 (P = .036). SUVmax threshold and donor type were independent factors for OS. Our results indicate that ¹⁸F-FDG-PET is highly accurate in identifying patients with acute intestinal GVHD and may predict responses to immunosuppressive therapy as well as survival, particularly when applied within the first 100 days after transplantation. These results provide a strong rationale to integrate PET imaging in future prospective trials evaluating new therapies for acute GVHD.

Pearls, Pitfalls, and Conditions that Mimic Mesenteric Ischemia at CT

Acute mesenteric ischemia (AMI) is a life-threatening condition with a high mortality rate. The diagnosis of AMI is challenging because patient symptoms and laboratory test results are often nonspecific. A high degree of clinical and radiologic suspicion is required for accurate and timely diagnosis. CT angiography of the abdomen and pelvis is the first-line imaging test for suspected AMI and should be expedited. A systematic "inside-out" approach to interpreting CT angiographic images, beginning with the bowel lumen and proceeding outward to the bowel wall, mesentery, vasculature, and extraintestinal viscera, provides radiologists with a practical framework to improve detection and synthesis of imaging findings. The subtypes of AMI are arterial and venoocclusive disease, nonocclusive ischemia, and strangulating bowel obstruction; each may demonstrate specific imaging findings. Chronic mesenteric ischemia is more insidious at onset and almost always secondary to atherosclerosis. Potential pitfalls in the diagnosis of AMI include mistaking pneumatosis as a sign that is specific for AMI and not an imaging finding, misinterpretation of adynamic ileus as a benign finding, and pseudopneumatosis. Several enterocolitides can mimic AMI at CT angiography, such as inflammatory bowel disease, infections, angioedema, and radiation-induced enterocolitis. Awareness of pitfalls, conditions that mimic AMI, and potential distinguishing clinical and imaging features can assist radiologists in making an early and accurate diagnosis of AMI. ^©RSNA, 2020.

Computed tomography imaging of acute gastrointestinal graft-versus-host disease after haematopoietic stem cell transplantation in children

Aim of the study

To evaluate computed tomography (CT) findings of gastrointestinal graft-versus-host disease (GI-GVHD) occurring in children after haematopoietic stem-cell transplantation (HSCT).

Material and methods

From February 2013 to May 2018, 225 paediatric patients underwent HSCT. Sixty-eight patients (30%) presented with clinical diagnosis of acute GI-GVHD in the first 100 days after HSCT. Thirty-five (18 girls, 17 boys; age range, 2–18 years; mean age, 10.3 years) of 68 patients had abdominopelvic CT and included in study.

Results

Intestinal CT abnormalities were present in 33 (94%) and extra-intestinal CT findings were in 30 (86%) patients. Thickening of the bowel wall was the most common finding (31 patients, 89%), which involved the small bowel in 29 patients (83%), colon in 16 patients (46%), and both in 15 patients (43%). Oesophageal wall thickening was present in three patients (9%), and gastric wall thickening was in eight patients (23%). Bowel dilatation was detected in 13 patients (37%). Mucosal enhancement of the bowel wall was observed in 28 patients (80%). The prevalence of the extra-intestinal CT findings were: periportal oedema in nine (26%), ascites in 15 (43%), wall thickening and enhancement of gall bladder in 13 (37%), pericholecystic fluid in six (17%), hepatomegaly in 13 (37%), and splenomegaly in nine (26%) patients. One patient (3%) demonstrated free intraperitoneal air due to intestinal perforation.

Conclusions

CT is useful to support the clinical diagnosis of acute GVHD in children with GI symptoms after HSCT. Radiological evaluation is important because early diagnosis and treatment affect the prognosis of GI-GVHD.

Acute graft-versus-host disease of the gut: considerations for the gastroenterologist

Haematopoietic stem cell transplantation (HSCT) is central to the management of many haematological disorders. A frequent complication of HSCT is acute graft-versus-host disease (GVHD), a condition in which immune cells from the donor attack healthy recipient tissues. The gastrointestinal system is among the most common sites affected by acute GVHD, and severe manifestations of acute GVHD of the gut portends a poor prognosis in patients after HSCT. Acute GVHD of the gastrointestinal tract presents both diagnostic and therapeutic challenges. Although the clinical manifestations are nonspecific and overlap with those of infection and drug toxicity, diagnosis is ultimately based on clinical criteria. As reliable serum biomarkers have not yet been validated outside of clinical trials, endoscopic and histopathological evaluation continue to be utilized in diagnosis. Once a diagnosis of gastrointestinal acute GVHD is established, therapy with systemic corticosteroids is typically initiated, and non-responders can be treated with a wide range of second-line therapies. In addition to treating the underlying disease, the management of complications including profuse diarrhoea, severe malnutrition and gastrointestinal bleeding is paramount. In this Review, we discuss strategies for the diagnosis and management of acute GVHD of the gastrointestinal tract as they pertain to the practising gastroenterologist.

Surgical treatment of intestinal complications of graft versus host disease in the pediatric population: Case series and review of literature

BACKGROUND/PURPOSE

Intestinal complications of acute graft-versus-host disease (aGVHD) include hemorrhage and perforation in the short-term, and stricture with bowel obstruction in the long-term. As medical management of severe aGVHD has improved, more patients are surviving even advanced stages of intestinal aGVHD. This review summarizes the available pediatric literature on surgical treatment of complications of intestinal GVHD.

METHODS

A systematic review was performed using PubMed, Cochrane, Embase, and Scopus databases. Any publication that addressed surgical treatment of acute and chronic intestinal GVHD in the pediatric population was reviewed in detail. Furthermore, we included information on 5 additional patients from the institutions of this review's authors, which had not been previously published.

RESULTS

We identified 8 studies, comprising 13 patients. Surgical interventions were undertaken for a variety of intestinal GVHD complications, including small bowel obstruction owing to stricture (n=8), enterocutaneous fistulae (n=2), gastrointestinal hemorrhage/perforation (n=1 each), and esophageal stricture (n=1). Among eight patients with bowel obstruction as an indication, pathology revealed ulceration with fibrosis in all but one; 3 had signs of persistent GVHD. Surgical mortality was reported in 4 patients (31%) at an average of 6weeks postoperatively. The median overall follow-up time was 20months (IQR, 2-21).

CONCLUSIONS

Although intestinal aGVHD management is almost exclusively medical, a small subset of patients develops complications of intestinal GVHD that require surgical intervention. With expanding indications for stem cell transplantation as well as improved survival after previously fatal bouts of intestinal aGVHD, it is likely that surgical intervention will become more common in these complicated patients.

SYSTEMATIC REVIEW

Level of Evidence: Level IV.

Imaging of Abdominal and Pelvic Manifestations of Graft-Versus-Host Disease After Hematopoietic Stem Cell Transplant

OBJECTIVE

Graft-versus-host disease (GVHD) is a common complication of hematopoietic stem cell transplant (HSCT). GVHD predominantly affects the skin, gastrointestinal system and hepatobiliary systems. Imaging findings in the gastrointestinal tract include bowel wall thickening with mucosal enhancement, mesenteric edema, and vascular engorgement. In the hepatobiliary system, hepatosplenomegaly, periportal edema, bile duct dilatation, and gallbladder and biliary wall thickening are seen. Although the imaging findings of GVHD are nonspecific, with a known history of HSCT, GVHD should be considered.

CONCLUSION

GVHD is a serious complication of HSCT, which involves multiple organ systems, with imaging manifestations most commonly seen in the gastrointestinal tract and hepatobiliary system. Knowledge of the imaging manifestations of GVHD, which alone may be relatively nonspecific, taken in conjunction with clinical history including the timing and type of HSCT, laboratory values, stool studies, and dermatologic findings can increase radiologist confidence in suggesting this diagnosis.

Outcomes of high-grade gastrointestinal graft-versus-host disease posthematopoietic stem cell transplantation in children

We explored the clinical course of acute high-grade gastrointestinal graft-versus-host disease in children in a single center. This was a retrospective analysis of 28 pediatric patients who presented with a clinical diagnosis of stage III and IV acute graft-versus-host disease (aGVHD) of the gastrointestinal system (GIS). Generally, skin involvement was the initial manifestation of aGVHD that began in the first 3 weeks of hematopoietic stem cell transplantation (HSCT); on the other hand, GIS involvement predominated after the second week of HSCT. Reported adult data show a survival rate of only 25%; however, our study showed more favorable outcomes in children with a survival rate of 55%. We monitored levels of albumin and immunoglobulin G and observed low levels overall during treatment of unresponsive patients, although only albumin levels were shown to be significantly different. We observed a significant increase in mortality with the use of antithymocyte globulin in GIS aGVHD, although antithymocyte globulin used for graft-versus-host disease prophylaxis had no demonstrable effect on GIS aGVHD mortality. Whether the significantly lower GIS aGVHD mortality among the children recruited in our study than among their historical adult counterparts is a primary result of the specific attributes of the pediatric GIS, or whether it originated from HSCT kinetics remains to be determined by future studies.

Ultrasonographic evaluation of gastrointestinal graft-versus-host disease after hematopoietic stem cell transplantation

Gastrointestinal graft‐versus‐host disease (GI‐GVHD) is a major and life‐threatening complication of hematopoietic stem cell transplantation (HSCT). This study evaluated the efficacy of ultrasonography (US) for assessing and monitoring GI‐GVHD. GI tract was evaluated by US in 81 patients. US findings were positive in 43 patients, including 11 false positive, and negative in 38 patients. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of US for the diagnosis of GI‐GVHD were 100%, 78%, 74%, 100%, and 86%, respectively. Diffuse wall thickening of the ileum was the most frequent finding in patients with GI‐GVHD. Severity of GI‐GVHD was correlated with the thickness of internal low echoic layer of the wall, the echogenicity of mesenteric fat tissue, and the intensity of Doppler signaling. We classified US findings of GI‐GVHD into four US grades. There was a significant correlation between clinical stage of GI‐GVHD and the US grade. These ultrasonographic abnormalities were improved with clinical improvement of GI‐GVHD upon treatment. Thus, US is an effective and efficient non‐invasive means of identifying the extent and severity of GI‐GVHD and monitoring response to treatment.

Assessment of acute intestinal graft versus host disease by abdominal magnetic resonance imaging at 3 Tesla

OBJECTIVES

After allogeneic stem cell transplantation (SCT), a reliable diagnosis of acute graft versus host disease (aGvHD) is essential for an early and successful treatment. It is the aim of this analysis to assess intestinal aGvHD by magnetic resonance imaging (MRI).

METHODS

Prior to allogeneic SCT, 64 consecutive patients underwent abdominal MRI examination on a 3 T MR system, including axial and coronal T2w sequences and a three-dimensional dynamic T1w, contrast enhanced sequence. After SCT, 20 patients with suspected aGvHD received a second MRI as well as an endoscopic examination.

RESULTS

Nine patients suffered from histologically proven intestinal aGvHD. In eleven patients intestinal aGvHD was excluded. In all aGvHD patients typical MRI findings with long-segment bowel wall thickening--always involving the terminal ileum--with profound submucosal oedema, were detected. The bowel wall was significantly thickened in patients with intestinal aGvHD. Bowel contrast enhancement spared the submucosa while demonstrating strong mucosal hyperemia.

CONCLUSIONS

In intestinal aGvHD, a characteristic MR-appearance can be detected. This MRI pattern might facilitate an early and non-invasive diagnosis of intestinal aGvHD. MRI might thus be used as a sensitive tool to rule out or support the clinical diagnosis of aGvHD.

KEY POINTS

• Acute intestinal graft versus host disease (aGvHD) can be assessed by MRI. • The aGvHD of the bowel demonstrates a characteristic MR imaging pattern. • Bowel wall shows extensive long-segment wall thickening with profound submucosal oedema. • Terminal ileum seems invariably affected; other bowel segments show variable involvement. • Colonoscopy in suspected aGvHD should include inspection of terminal ileum.