Robert Riddell, M.D., F.R.C.Path, F.R.C.P.C.



Dr. Robert RiddellDr. Robert Riddell graduated from the University of London (St. Bartholomew's Hospital) and trained in GI Pathology at St. Mark's and St. Bartholomew's Hospitals in London. Following his Boards Examination, he went to the University of Chicago in 1974 as an Assistant Professor and was promoted to Associate Professor in 1979. In 1984, he moved to McMaster University Medical Centre in Hamilton, Ontario as Professor of Pathology (now Molecular Medicine and Pathobiology). He also was Chief of Service for Anatomical Pathology at McMaster University Medical Centre. In 2001, he moved to Mount Sinai Hospital where he is Head of the Sections of Gastrointestinal Pathology and Immunopathology and Professor of Laboratory Medicine and Pathobiology at the University of Toronto.

Dr. Riddell has over 230 publications which are largely in gastrointestinal pathology. Many of them are in inflammatory bowel disease. In 1983, Dr. Riddell was lead author on the paper defining and grading dysplasia in inflammatory bowel disease, a system that is not only still in use but has been extended to other part of the gastrointestinal tract. He is interested in all forms of inflammatory and neoplastic disease throughout the GI tract. He has edited or written 5 books, which include a two volume "bible" on gastrointestinal pathology and its clinical implications with Drs. Klaus Lewin and Wilfred Weinstein at UCLA.

This book is currently being re-written. He is also the lead author of the AFIP Fascicle on tumors of the intestines. Dr. Riddell directs an annual week long gastrointestinal pathology course that has now been running for almost 30 years. He is a frequent speaker and talks about intestinal disease in both the upper and lower gastrointestinal tract both nationally and internationally. He has numerous on-going projects including gastroesophageal reflux disease, indeterminate colitis, drug-associated colitis, and molecular changes in dysplasia in ulcerative colitis and the pathology of motility disorders.



Medical Secretary
Paula Nixon
Phone: 416-586-4800 x 8816
Fax: 416-586-8481

Office Location
Mount Sinai Hospital
Joseph and Wolf Lebovic Health Complex
6-502-4, 600 University Avenue
Toronto, Ontario, Canada
M5G 1X5


  • Riddell RH, editor: The Pathology of Drug?Induced and Toxic Diseases. New York: Churchill?Livingstone, 1982.
  • Riddell RH, Goldman H, Ransohoff DF, Appelman H, Fenoglio C, Haggitt R, Ahren C, Correa P, Hamilton S, Morson BC, Sommers SC, Yardley JH: Dysplasia in inflammatory bowel disease: Standardized classification with provisional clinical recommendations. Hum Pathol 1983; 14:931?968
  • Lewin K, Riddell RH, Weinstein WM: Gastrointestinal Pathology and Its Clinical Implications. New York: Igaku-Shoin, 1992.
  • Riddell RH, Tanaka M, Mazzoleni G: Non-steroidal anti-inflammatory
  • Dixon MF, Genta RM, Yardley J, Correa P on behalf of the participants in the Houston Gastritis Workshop: Batts KP, Dahms BB, Filipe MI, Haggitt RC, Haot J, Hui PK, Lechago J, Lewin K, Offerhaus JA, Price AB, Recavarren S, Riddell RH, Sipponen P, Solcia E, Stolte M, Watanabe H: Classification and grading of gastritis. The up-dated Sydney System. Am J Surg Path 1996: 20(10): 1161-1181.
  • Wright CL, Riddell RH. Histology of the stomach and duodenum in Crohn’s disease. Amer J Sur Pathol 1998;22(4):383-390
  • Tanaka M, Riddell RH, Soma Y, Saito H, Hidaka H, Kudo H. Morphologic criteria applicable to biopsy specimens for effective distinction of Crohn's disease, ulcerative colitis and other forms of colitis. Scand J Gastroenterol 1999;34(1):55-67.
  • Schlemper RJ, Riddell RH, Kato Y, Borchard F, Cooper HS, Dawsey SM, Dixon MF, Fenoglio-Preiser CM, Flejou JF, Geboes K, Hattori T, Hirota T, Itabashi M, Iwafuchi M, Iwashita A, Kim YI, Kirchner T, Klimpfinger M, Koike M, Lauwers GY, Lewin KJ, Oberhuber G, Offner F, Price AB, Rubio CA, Shimizu M, Shimoda T, Sipponen P, Solcia E, Stolte M, Watanabe H, Yamabe H. The Vienna classification of gastrointestinal epithelial neoplasia. Gut. 2000;47(2):251-5.
  • Streutker CJ, Bernstein CN, Chan VL, Riddell RH, Croitoru K. Detection of species-specific helicobacter ribosomal DNA in intestinal biopsies. Samples from a population-based cohort of patients with ulcerative colitis. J Clin Microbiol. 2004;(2):660-4.
  • Riddell RH, Montgomery, E. Traps in the Diagnosis of Ulcerative Colitis. Pathology Case Reviews. 2004;9(3):87-92
  • Montgomery E, Riddell RH. Ischemic Colitis in a Young Patient (pg. 97). Pathology Case Reviews. 2004;9(3):93-95.
  • Silverberg MS, Satsangi J, Ahmad T, Arnott I, Bernstein CN, Brant MD, Caprilli R,Colombel JF, Gasche C, Geboes K, Jewell DP, Karban A, Loftus EV, Peña AS, Riddell RH, Sachar DB, Schreier S, Steinhart AH, Targan SR, Vermeire S, Warren BF. Toward an integrated clinical, molecular and serological classification of inflammatory Bowel disease: Report of a Working Party of the 2005 Montreal World Congress of Gastroenterology. Can J Gastroenterol. 2005;19 Suppl A:5-36.
  • Haddad S, Riddell RH. The role of eosinophils in inflammatory bowel disease. Gut. 2005;54(12):1674-5.
  • Kirsch R, Gao ZH, Riddell, RH. Gastrointestinal stromal tumors: diagnostic challenges and practical approach to differential diagnosis. Adv Anat Pathol. 2007 Jul;14(4):261-85.
  • Riddell RH, Odze RD. Definition of Barrett's esophagus: time for a rethink--is intestinal metaplasia dead? Am J Gastroenterol. 2009 Oct;104(10):2588-94. Epub 2009 Jul 21. Review.
  • Maguire AA, Greenson JK, Lauwers GY, Ginsburg RE, Williams GT, Brown IS, Riddell RH, O'Donoghue D, Sheahan KD. Collagenous sprue: a clinicopathologic study of 12 cases. Am J Surg Pathol. 2009 Oct;33(10):1440-9.
  • Terry J, Torlakovic EE, Garratt J, Miller D, Köbel M, Cooper J, Bahzad S, Pilavdzic D, O'Malley F, O'Brien AE, SenGupta S, Alport E, Têtu B, Knight B, Pettigrew NM, Berendt R, Wolber R, Trotter MJ, Riddell RH, Gaboury L, Elms F, Magliocco A, Barnes P, Gown AM, Gilks CB. Implementation of a Canadian external quality assurance program for breast cancer biomarkers: an initiative of Canadian Quality Control in immunohistochemistry (cIQc) and Canadian Association of Pathologists (CAP) National Standards Committee/Immunohistochemistry. Appl Immunohistochem Mol Morphol. 2009 Oct;17(5):375-82.
  • Ryan P, Nguyen VH, Gholoum S, Carpineta L, Abish S, Ahmed NN, Laberge JM, Riddell RH. Polypoid PEComa in the rectum of a 15-year-old girl: case report and review of PEComa in the gastrointestinal tract. Am J Surg Pathol. 2009 Mar;33(3):475-82.
  • Kirsch R, Geboes K, Shepherd NA, de Hertogh G, Di Nicola N, Lebel S, Mickys U, Riddell RH. Systemic mastocytosis involving the gastrointestinal tract: clinicopathologic and molecular study of five cases. Mod Pathol. 2008 Dec;21(12):1508-16. Epub 2008 Oct 17.
  • Dickson BC, Chung CT, Patterson BJ, Riddell RH, Kamel-Reid S, Messner HA, Lipton JH. Precursor lymphoblastic lymphoma reoccurring as a donor-derived neoplasm: a case report and review of the literature. Arch Pathol Lab Med. 2008 Aug;132(8):1342-5. Review.
  • Geboes K, Colombel JF, Greenstein A, Jewell DP, Sandborn WJ, Vatn MH, Warren B, Riddell RH; Pathology Task Force of the International Organization of Inflammatory Bowel Diseases. Indeterminate colitis: a review of the concept--what's in a name? Inflamm Bowel Dis. 2008 Jun;14(6):850-7. Review.
  • Rubin DT, Cruz-Correa MR, Gasche C, Jass JR, Lichtenstein GR, Montgomery EA, Riddell RH, Rutter MD, Ullman TA, Velayos FS, Itzkowitz S; 5-ASA in Colorectal Cancer Prevention Meeting Group. Colorectal cancer prevention in inflammatory bowel disease and the role of 5-aminosalicylic acid: a clinical review and update. Inflamm Bowel Dis. 2008 Feb;14(2):265-74. Review.
  • Jass JR, O'Brien J, Riddell RH, Snover DC; Association of Directors of Anatomic and Surgical Pathology. Recommendations for the reporting of surgically resected specimens of colorectal carcinoma: Association of Directors of Anatomic and Surgical Pathology. Am J Clin Pathol. 2008 Jan;129(1):13-23.
  • Jass JR, O'Brien MJ, Riddell RH, Snover DC; Association of Directors of Anatomic and Surgical Pathology. Recommendations for the reporting of surgically resected specimens of colorectal carcinoma. Hum Pathol. 2007 Apr;38(4):537-545. Epub 2007 Feb 1.
  • Jass JR, O'Brien MJ, Riddell RH, Snover DC; Association of Directors of Anatomic and Surgical Pathology (ADASP). Recommendations for the reporting of surgically resected specimens of colorectal carcinoma.Virchows Arch. 2007 Jan;450(1):1-13. Epub 2006 Nov 25.
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