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John Tillou, MD, is a board-certified colon and rectal surgeon at Fairfax Colon & Rectal Surgery, PC. He has wanted to be a surgeon since undergoing an operation in high school.

A native of Norfolk, Virginia, Dr. Tillou received his Bachelor of Science in Chemistry at the University of Utah in Salt Lake City, Utah, where he made the Dean’s List, coached high school baseball, worked in a pathology lab, and volunteered at a free medical clinic. 

During his undergraduate studies, he earned the Bioscience Undergraduate Research Mini-grant and received the Comprehensive Chemistry Award and Undergraduate Research Scholar award.

Dr. Tillou eventually returned home to attend medical school at the University of Virginia School of Medicine in Charlottesville, Virginia, where he received the Dr. Graham Clark Scholarship and the Charles & Bernice McKay Scholarship.

After graduation, Dr. Tillou completed his general surgery residency at Beth Israel Deaconess Medical Center, a teaching hospital of Harvard Medical School in Boston, Massachusetts. He completed an additional colorectal surgery fellowship at MedStar Washington Hospital Center in Washington, D.C.

While completing his training, Dr. Tillou co-authored several book chapters and papers. He also received the highest score on the annual colorectal training exam.

Dr. Tillou has undergone advanced training in minimally invasive, robotic, and transanal colon and rectal surgery techniques. He has a particular interest in the treatment and management of colon cancer, anal pain, and anal cancer.

In addition, Dr. Tillou holds many professional affiliations, including the American Society of Colon & Rectal Surgeons, American College of Surgeons, Medical Society of Virginia, and Chesapeake Colorectal Society.

Outside of work, Dr. Tillou enjoys hiking, skiing, playing guitar, and spending time with his family.

John Tillou, MD, is a board-certified colon and rectal surgeon at Fairfax Colon & Rectal Surgery, PC. He has wanted to be a surgeon since undergoing an operation in high school.

A native of Norfolk, Virginia, Dr. Tillou received his Bachelor of Science in Chemistry at the University of Utah in Salt Lake City, Utah, where he made the Dean’s List, coached high school baseball, worked in a pathology lab, and volunteered at a free medical clinic. 

During his undergraduate studies, he earned the Bioscience Undergraduate Research Mini-grant and received the Comprehensive Chemistry Award and Undergraduate Research Scholar award.

Dr. Tillou eventually returned home to attend medical school at the University of Virginia School of Medicine in Charlottesville, Virginia, where he received the Dr. Graham Clark Scholarship and the Charles & Bernice McKay Scholarship.

After graduation, Dr. Tillou completed his general surgery residency at Beth Israel Deaconess Medical Center, a teaching hospital of Harvard Medical School in Boston, Massachusetts. He completed an additional colorectal surgery fellowship at MedStar Washington Hospital Center in Washington, D.C.

While completing his training, Dr. Tillou co-authored several book chapters and papers. He also received the highest score on the annual colorectal training exam.

Dr. Tillou has undergone advanced training in minimally invasive, robotic, and transanal colon and rectal surgery techniques. He has a particular interest in the treatment and management of colon cancer, anal pain, and anal cancer.

In addition, Dr. Tillou holds many professional affiliations, including the American Society of Colon & Rectal Surgeons, American College of Surgeons, Medical Society of Virginia, and Chesapeake Colorectal Society.

Outside of work, Dr. Tillou enjoys hiking, skiing, playing guitar, and spending time with his family.

John Tillou, MD, is a board-certified colon and rectal surgeon at Fairfax Colon & Rectal Surgery, PC. He has wanted to be a surgeon since undergoing an operation in high school.

A native of Norfolk, Virginia, Dr. Tillou received his Bachelor of Science in Chemistry at the University of Utah in Salt Lake City, Utah, where he made the Dean’s List, coached high school baseball, worked in a pathology lab, and volunteered at a free medical clinic. 

During his undergraduate studies, he earned the Bioscience Undergraduate Research Mini-grant and received the Comprehensive Chemistry Award and Undergraduate Research Scholar award.

Dr. Tillou eventually returned home to attend medical school at the University of Virginia School of Medicine in Charlottesville, Virginia, where he received the Dr. Graham Clark Scholarship and the Charles & Bernice McKay Scholarship.

After graduation, Dr. Tillou completed his general surgery residency at Beth Israel Deaconess Medical Center, a teaching hospital of Harvard Medical School in Boston, Massachusetts. He completed an additional colorectal surgery fellowship at MedStar Washington Hospital Center in Washington, D.C.

While completing his training, Dr. Tillou co-authored several book chapters and papers. He also received the highest score on the annual colorectal training exam.

Dr. Tillou has undergone advanced training in minimally invasive, robotic, and transanal colon and rectal surgery techniques. He has a particular interest in the treatment and management of colon cancer, anal pain, and anal cancer.

In addition, Dr. Tillou holds many professional affiliations, including the American Society of Colon & Rectal Surgeons, American College of Surgeons, Medical Society of Virginia, and Chesapeake Colorectal Society.

Outside of work, Dr. Tillou enjoys hiking, skiing, playing guitar, and spending time with his family.

Terah C. Isaacson, MD, FACS, is a highly skilled and experienced general and colorectal surgeon at Bayou City Surgical Specialists in Houston, Texas. She is also a founding partner and has been dedicated to providing exceptional surgical care since 2016. 

With a robust educational background and extensive professional experience, Dr. Isaacson has established herself as a leader in her field. She completed her fellowship in colon & rectal surgery at the University of Texas Affiliated Hospitals in Austin and her residency in general surgery at Oregon Health & Science University in Portland. Dr. Isaacson earned her Doctor of Medicine from the University of Kansas School of Medicine in Kansas City and holds a Bachelor of Arts in biochemistry from the University of Kansas in Lawrence. 

She is a fellow of the American College of Surgeons and the American Society of Colon & Rectal Surgeons and holds active medical licenses in Texas, Kansas, and Tennessee. 

Dr. Isaacson's clinical skills include advanced training in colorectal robotics, and laparoscopic surgery. She has contributed to medical literature, including a book chapter in "Complexities in Colorectal Surgery" and multiple abstracts and presentations at professional conferences.

To schedule an appointment with Dr. Isaacson, call the office or reach out online today.

Daniel Lee Howell, Jr., MD, FACS is a renowned expert in colorectal surgery with extensive experience managing complex anorectal issues. He offers expert and compassionate care to patients at Bayou City Surgical Specialists in Houston, Texas. 

Dr. Howell is highly skilled in various outpatient operative techniques, proficient in laparoscopy and minimally invasive methods for treating intra-abdominal conditions, and adept in both diagnostic and therapeutic endoscopy, ensuring comprehensive care for his patients.

Dr. Howell is an active member of the American College of Surgeons, the Texas Medical Association, and the Harris County Medical Society. His patient-centered approach emphasizes clear communication, ensuring that patients fully understand their conditions and treatment options. He firmly believes in the importance of patient education, stating, "If you don't understand what you have, I haven't done my job."

Residing in Houston, Dr. Howell enjoys biking around the city, participating in his children's sports activities, and honing his skills as an amateur barbecue chef. He prefers spending his free time outdoors but also enjoys watching sporting events indoors.

Anna Kata, MD, MAS, is a board-certified general surgeon and board-eligible colorectal surgeon-October 2024 and proctologist at Fairfax Colon & Rectal Surgery, PC. She serves patients in and around Fairfax, Gainesville, and Lansdowne, Virginia, operating out of FCRS’s Fairfax - Merrifield, Fairfax – Gainesville/Haymarket, and Lansdowne - Loudoun offices. 

Born and raised in northern New Jersey, Dr. Kata recognized her passion for medicine early on while volunteering in the surgical wards of her local hospital. She saw firsthand the impact a thoughtful and well-trained physician could have on the lives of their patients. With this goal in mind, she obtained her Bachelor of Science in Biology at Yale University in New Haven, Connecticut.

After graduation, Dr. Kata moved and enrolled at the University of California, San Francisco’s School of Medicine. There, she cemented her desire to become a surgeon and subsequently completed her surgical training at MedStar Georgetown University Hospital in Washington, DC. 

Wanting further expertise, Dr. Kata pursued a Colon and Rectal Surgical Fellowship at Lahey Hospital & Medical Center in Burlington, Massachusetts. Her training included all aspects of anorectal and abdominal surgery and endoscopy. 

During her clinical training, Dr. Kata developed an interest in the issues surrounding the care of older adults undergoing surgery. To further study this topic, she obtained a master’s in Clinical Research at her alma mater, the University of California, San Francisco. She has authored several publications and presented her research at national meetings. 

When she isn’t at work, Dr. Kata enjoys spending time outdoors with her husband and is an avid backpacker and gardener. 

Anna Kata, MD, MAS, is a board-certified general surgeon and board-eligible colorectal surgeon-October 2024 and proctologist at Fairfax Colon & Rectal Surgery, PC. She serves patients in and around Fairfax, Gainesville, and Lansdowne, Virginia, operating out of FCRS’s Fairfax - Merrifield, Fairfax – Gainesville/Haymarket, and Lansdowne - Loudoun offices. 

Born and raised in northern New Jersey, Dr. Kata recognized her passion for medicine early on while volunteering in the surgical wards of her local hospital. She saw firsthand the impact a thoughtful and well-trained physician could have on the lives of their patients. With this goal in mind, she obtained her Bachelor of Science in Biology at Yale University in New Haven, Connecticut.

After graduation, Dr. Kata moved and enrolled at the University of California, San Francisco’s School of Medicine. There, she cemented her desire to become a surgeon and subsequently completed her surgical training at MedStar Georgetown University Hospital in Washington, DC. 

Wanting further expertise, Dr. Kata pursued a Colon and Rectal Surgical Fellowship at Lahey Hospital & Medical Center in Burlington, Massachusetts. Her training included all aspects of anorectal and abdominal surgery and endoscopy. 

During her clinical training, Dr. Kata developed an interest in the issues surrounding the care of older adults undergoing surgery. To further study this topic, she obtained a master’s in Clinical Research at her alma mater, the University of California, San Francisco. She has authored several publications and presented her research at national meetings. 

When she isn’t at work, Dr. Kata enjoys spending time outdoors with her husband and is an avid backpacker and gardener. 

Anna Kata, MD, MAS, is a board-certified general surgeon and board-eligible colorectal surgeon-October 2024 and proctologist at Fairfax Colon & Rectal Surgery, PC. She serves patients in and around Fairfax, Gainesville, and Lansdowne, Virginia, operating out of FCRS’s Fairfax - Merrifield, Fairfax – Gainesville/Haymarket, and Lansdowne - Loudoun offices. 

Born and raised in northern New Jersey, Dr. Kata recognized her passion for medicine early on while volunteering in the surgical wards of her local hospital. She saw firsthand the impact a thoughtful and well-trained physician could have on the lives of their patients. With this goal in mind, she obtained her Bachelor of Science in Biology at Yale University in New Haven, Connecticut.

After graduation, Dr. Kata moved and enrolled at the University of California, San Francisco’s School of Medicine. There, she cemented her desire to become a surgeon and subsequently completed her surgical training at MedStar Georgetown University Hospital in Washington, DC. 

Wanting further expertise, Dr. Kata pursued a Colon and Rectal Surgical Fellowship at Lahey Hospital & Medical Center in Burlington, Massachusetts. Her training included all aspects of anorectal and abdominal surgery and endoscopy. 

During her clinical training, Dr. Kata developed an interest in the issues surrounding the care of older adults undergoing surgery. To further study this topic, she obtained a master’s in Clinical Research at her alma mater, the University of California, San Francisco. She has authored several publications and presented her research at national meetings. 

When she isn’t at work, Dr. Kata enjoys spending time outdoors with her husband and is an avid backpacker and gardener. 

Dr. Rolando H. Saenz, MD, is a dual board-certified general and colorectal surgeon. He offers a variety of surgical services to patients of Downtown San Antonio and nearby areas in Texas at his practice, San Lucas Surgical Associates. As one of the leading general and colorectal surgeons in San Antonio, he understands the unique needs of each patient and attends to them in a caring and compassionate manner.

Dr. Saenz completed his medical degree at the University of Texas Health Science Center in San Antonio, Texas. He then spent two years as a surgical resident at the Chicago Medical School in North Chicago, Illinois.

His passion for specialized care led him to open this forward-thinking private practice in San Antonio, Texas. Dr. Saenz has operated on thousands of patients during his three decades of general and colorectal surgical practice, with excellent results. He is equipped to perform the latest cutting-edge surgical procedures and is particularly adept at colon cancer surgery.

Dr. Saenz believes in educating patients about their disease and encourages them to follow a healthy lifestyle as they heal. He ensures his patients feel comfortable by helping them understand the disease and how surgical intervention will work.

He is an active member of the San Antonio medical community and is affiliated with the Baptist Health System, Nix Health, Methodist Specialty and Transplant Hospital, Methodist Hospital, Northeast Methodist Hospital, and the Metropolitan Methodist Hospital.

He was born and raised in San Antonio, and his equal fluency in English and Spanish allows him to treat patients from a diverse cultural background. To schedule an appointment with Dr. Saenz, call San Lucas Surgical Associates today.

Board-certified colorectal surgeon Ren yu Zhang, MD, has dedicated his medical career to helping patients suffering from conditions affecting the colon, rectum, and anus. At his practice in Las Vegas, Nevada, he prides himself on putting his patients first, taking the time to listen to their concerns and goals before offering an individualized treatment plan.

Dr. Zhang hails from the east coast. He graduated from the University of Rochester, majoring in Electrical Engineering and Developmental Biology. He then went on to earn his medical degree at the University of Rochester School of Medicine and Dentistry. Subsequently, he completed his general surgery training at Strong Memorial Hospital in Rochester under internationally renowned surgeons, including Dr. Seymour Schwartz.

During his general surgery residency, he spent a year completing fellowship research at Cleveland Clinic, focusing on surgical outcomes in colorectal surgery. Under the guidance of Dr. Victor Fazio, his research projects were presented at various national conferences. Before joining Nevada Surgery and Cancer Care, he completed his fellowship training in colorectal surgery in Erie, Pennsylvania.

Focusing on the care and protection of your colon and rectal health, Dr. Zhang is committed to delivering the highest quality in comprehensive specialty care. Interested in both benign and malignant conditions of the colon and the rectum, he provides management and treatment of a wide range of conditions such as anorectal fistula, abscesses, anal fissure, hemorrhoids, anal/colon/rectal cancers, bowel incontinence, rectal prolapse, diverticular disease, colostomy/ileostomy, Crohn’s disease, and ulcerative colitis.

Utilizing state-of-the-art technology, Dr. Zhang offers minimally invasive robot/laparoscopic colon and rectal resection to help you with faster recovery and lesser pain in addition to comprehensive care in the cancer field ranging from a screening colonoscopy to a therapeutic colonoscopic polyp removal. Sensitive to your anxieties and concerns with anorectal or colorectal disease, Dr. Zhang will work closely with you to alleviate any physical and emotional stress to achieve the best outcomes for you. He also provides comprehensive care in the field of maintaining colon and rectal health, ranging from screening colonoscopies to therapeutic colonoscopic polyp removal.

Since he completed his training, Dr. Zhang has been in practice in Las Vegas. He looks forward to continuing to provide individualized care to the people of our community.

Michael Zehnpfennig, MD, is a fellowship-trained colorectal surgeon who offers exceptional patient-focused care at Montana Colon in Missoula, Montana. Until recently, patients with conditions such as complex anorectal disease, colorectal cancer, and inflammatory bowel disease had to travel outside of Montana to consult a fellowship-trained colorectal specialist, but with Dr. Zehnpfennig, Montanans can stay in Montana for their specialized care.

Dr. Zehnpfennig graduated with honors in 2006 from Wayne State University School of Medicine in Detroit, Michigan. His interest in colon and rectum surgery drives him to seek out the best and most innovative treatments that offer patients relief from pain and an improved quality of life.

Some of the advanced surgeries Dr. Zehnpfennig performs include endorectal advancement flap and ligation of intersphincteric fistula tract (LIFT) for complex anal fistulas, transanal minimally invasive surgery (TAMIS) for rectal cancer, and the NICE procedure (natural orifice intracorporeal anastomosis with extraction of specimen) for colon resection. He's often able to use single-incision laparoscopic surgery (SILS) techniques to minimize tissue damage and pain.

Dr. Zehnpfennig is also highly skilled in robotic surgery. He uses the da Vinci® Xi platform to perform a variety of procedures, including parastomal, preperitoneal, and retrorectus hernia repairs, ventral mesh rectopexy (VMR) for rectal prolapse, transversus abdominis release (TAR procedure) for large midline hernias and abdominal wall reconstruction, and the hybrid laparoscopic/robotic extended totally extraperitoneal (eTEP) approach to complex abdominal wall hernias.

In addition to cutting-edge surgery, Dr. Zehnpfennig also offers interventions for treating hemorrhoids, cosmetic resection of anal skin tags, and Botox® injections for the non-surgical treatment of anal fissures. 

Patients at Montana Colon benefit from the use of leading technologies that offer the ultimate in safety and efficiency and deliver superior results, such as the Ethicon ENSEAL® powered surgical stapler, Bard™ Soft Mesh, laparoscopic video technology from Stryker, and Olympus endoscopy equipment.

Find out more about the unrivaled services patients receive at Montana Colon by calling its office today or booking an appointment online. 

Shirley began her medical career at just 17-years-old as a Certified Nursing Assistant at Northside Hospital Gwinnett. She worked night shifts all while completing her bachelor of science degree in Cellular Biology and Biotechnology at Georgia Gwinnett College in Lawrenceville, GA. From there, Shirley went on to receive her master’s degree in Interdisciplinary Anatomy and Physiology at Touro University in New York. Following that, she completed her Physician Assistant degree at St. Elizabeth University in New Jersey.

Shirley serves as a physician assistant not only at Comprehensive Primary Care, but at Colon and Rectal Clinic as well. She is dedicated to providing thorough and detailed care to each one of her patients. She is bilingual in Spanish and is from the Gwinnett area. When she is not seeing patients, Shirley enjoys traveling regularly and spends any extra time with her family.

Shirley began her medical career at just 17-years-old as a Certified Nursing Assistant at Northside Hospital Gwinnett. She worked night shifts all while completing her bachelor of science degree in Cellular Biology and Biotechnology at Georgia Gwinnett College in Lawrenceville, GA. From there, Shirley went on to receive her master’s degree in Interdisciplinary Anatomy and Physiology at Touro University in New York. Following that, she completed her Physician Assistant degree at St. Elizabeth University in New Jersey.

Shirley serves as a physician assistant not only at Comprehensive Primary Care, but at Colon and Rectal Clinic as well. She is dedicated to providing thorough and detailed care to each one of her patients. She is bilingual in Spanish and is from the Gwinnett area. When she is not seeing patients, Shirley enjoys traveling regularly and spends any extra time with her family.

Shirley began her medical career at just 17-years-old as a Certified Nursing Assistant at Northside Hospital Gwinnett. She worked night shifts all while completing her bachelor of science degree in Cellular Biology and Biotechnology at Georgia Gwinnett College in Lawrenceville, GA. From there, Shirley went on to receive her master’s degree in Interdisciplinary Anatomy and Physiology at Touro University in New York. Following that, she completed her Physician Assistant degree at St. Elizabeth University in New Jersey.

Shirley serves as a physician assistant not only at Comprehensive Primary Care, but at Colon and Rectal Clinic as well. She is dedicated to providing thorough and detailed care to each one of her patients. She is bilingual in Spanish and is from the Gwinnett area. When she is not seeing patients, Shirley enjoys traveling regularly and spends any extra time with her family.

Burzeen E. Karanjawala, MD, is a colorectal surgeon at Sacramento Colon and Rectal Surgery Medical Group. He sees patients at the Sacramento and Roseville, California, offices. 

Dr. Karanjawala obtained a Bachelor of Arts in molecular and cell biology from the University of California, Berkeley. He also earned a Master of Science in physiology and biophysics from Georgetown University in Washington, DC. 

Dr. Karanjawala graduated from medical school at New York Medical College in Valhalla, New York. He did his general surgery residency training at the University of Texas Health Science Center in Houston, Texas. He then completed his colon and rectal surgery residency at UT Physicians Colon and Rectal Clinic – Texas Medical Center in Houston, Texas. 

Dr. Karanjawala worked for two years at the Lyndon B. Johnson General Hospital in Houston, Texas, first as a clinical instructor and then as an assistant professor. 

He is board certified in both general surgery and colon and rectal surgery. Dr. Karanjawala has an interest in a wide variety of colorectal disorders. He is passionate about minimally invasive surgery and robotic surgery. He is also skilled at endoscopy and is keen on the surgical management of inflammatory bowel disease.

2023 Sutter Independent Physicians President’s Award Recipient for Excellence in Patient Care