Meet Our Skilled Team of Vets & Hospital Manager

Spencer Animal Hospital has some of the most committed, caring veterinarians in Pasadena and a dedicated hospital staff! We are a group of passionate, pet-loving professionals who strive to deliver the highest level of excellence to each and every one of our patients. Learn about us online, and make an appointment soon to meet us in person! Call us at (281) 476-0066 to schedule an appointment today.

Interested in joining our team? Apply online!

Dennis Mangum, DVM

Dennis Mangum


A 1971 graduate of the College of Veterinary Medicine at Texas A&M University, Dr. Dennis Mangum loves interacting with people and their pets. He made veterinary medicine his career decision when he was in the fourth grade. After graduating from high school in the East Texas town of Canton, Dr. Mangum continued his studies, never wavering from his goal—to become a veterinarian. After receiving his DVM, Dr. Mangum settled in Pasadena, where, in 1974, he opened the original Spencer Animal Hospital in a small shopping center. In 1979, that practice relocated to our current award-winning facility dedicated to the continuation of providing quality animal health care.

Dr. Mangum’s professional credits include memberships in the American Veterinary Medical Association, Texas Veterinary Medical Association, Harris County Veterinary Medical Association, and the Texas Academy of Veterinary Practice. Additionally, Spencer Animal Hospital is accredited by the American Animal Hospital Association, of which Dr. Mangum is also a member.

Outside of veterinarian medicine, Dr. Mangum serves as a Deacon of his church and enjoys flying (he is a Certified Flight Instructor). His other hobbies include running and biking. Dr. Mangum and his wife have three daughters, four grandsons, and two granddaughters. Two of his daughters and a son-in-law followed his footsteps to Texas A&M. His middle daughter, Alaina, is the Practice Manager of Spencer Animal Hospital.

Helene Norton, DVM
Helene Norton, DVM

Helene Norton


Dr. Helene Norton grew up in Southern California and received her bachelor’s degree in animal science in 2012 from California Polytechnic State University San Luis Obispo, a small town in Central Coast California. Loving adventure and traveling, she then attended veterinary school at Ross University on St. Kitts and Nevis Island in the Caribbean, followed by a year of clinical rotations at the Louisiana State University Animal Teaching Hospital. After receiving her Doctorate in Veterinary Medicine in 2015, she moved back to Central Coast California to work as a veterinarian in an emergency animal clinic. In January 2017, she moved to the state of Texas following her husband's new job at NASA; and we welcomed her into our practice as a full-time associate veterinarian.

Dr. Norton settled immediately in the Texan way of life and became a member of the Houston Rodeo and Livestock Show Veterinary Committee, which is involved in testing livestock for performance-enhancing substances and antibiotics that could potentially be detrimental to human health. She is especially interested in soft tissue surgery, dentistry, emergency, and preventative medicine.

She lives with her husband, Chris, her son, Travis, and their two dogs, Zoe and Arya. Zoe was rescued off the streets of the Caribbean Island of St. Kitts as a young puppy. Although she is a mutt, we like to call her a “coconut retriever.” Arya is a German Shepherd who loves to show off her tricks and needs lots of love and attention. In her free time, Dr. Norton enjoys hiking, camping, traveling, and spending time with family.

Dr. Simon

Cesar Simon-Vazquez


Dr. Cesar Simon-Vazquez was born in Madrid, Spain. Due to the love he had for medicine and animals, he knew that being a Veterinarian was in his future.

Dr. Simon first began working on a rabbit farm in Spain around 1990, and then moved his way up through practicing as a freelance surgeon. In 1995, Dr. Simon began practicing as a veterinarian for a small animal practice. He moved to England, UK around 1998 and practiced veterinary medicine for about 10 years. In 2008, he moved to Bastrop, Texas. In 2011, Dr. Simon passed his North American Veterinary Licensing. In 2013, he became certified through the Educational Commission for Foreign Veterinary Graduates. Lastly, in 2013, Dr. Simon became certified through the Texas Board of Veterinary Medical Examiners.

Dr. Simon has a Texas-born son and a greyhound mixed breed, Flaca, which was rescued from the Houston SPCA. Last, but certainly not least, he has a bearded dragon named Shaggy!

Dr. Simon enjoys spending time with his son, as he is the joy of his life. If time allows, he will hit up the gym to get in a good workout. Dr. Simon also enjoys reading with a special interest in history, philosophy and psychology.

We are so pleased Dr. Simon is a part of our practice. Did we mention that he is bilingual?

Dr. Penn

Andrew Penn


Dr. Andrew Penn grew up locally in Pearland, Texas. He received his bachelors in Biomedical Science from Texas A&M University in 2014, and was granted his Doctorate of Veterinary Medicine in early 2020 also from Texas A&M University.


Dr. Penn is a doting cat dad of two neutered male domestic shorthair cats named Calvin and Hobbes.


Dr. Penn likes to spend his downtime spending time with his cats and has recently been training them to run on an exercise wheel. His other hobbies include ballroom dancing, which he has competed in collegiately during both his times at A&M.



Hospital Manager

Alaina has worked at Spencer Animal Hospital since graduating from Texas A&M University in May 2004—although really, she’s been around Pasadena since she was born. Dr. Mangum is her father and has had her doing things around the hospital since she can remember. Alaina loves her job! And getting to be around furry pets in a loving atmosphere is an excellent perk, too.

She spends her spare time flying and having fun with her son, daughter, and husband.

Call us at 281-476-0066 to schedule your next visit with one of out expert veterinarians today.