CT scans at WHOI diagnose ear infection in Townsend

harbor seal

On the surface, Townsend the harbor seal looks healthy. He is active, alert, eating, and of good body weight. Unfortunately, as with many wild animals, his demeanor hides a serious illness.

Discharge from Townsend's left ear.As we reported last month, shortly after arrival we noticed a discharge coming from Townsend’s left ear. We feared this could mean he had an ear infection which, for a variety of reasons related to their anatomy, often is very serious in seals. We cultured the discharge and performed an on-site “canalography” (x-ray with contrast dye) but the results were inconclusive.

So we turned to our friends at the Computerized Scanning and Imaging (CSI) Facility at the Woods Hole Oceanographic Institution for help. Facility director Dr. Darlene Ketten and her associates Julie Arruda, and Scott Cramer seek to understand how the ears of marine animals, particularly whales and dolphins, are able to hear and use underwater sounds. They use state-of-the-art biomedical imaging techniques, specifically CT (computed tomography) and MRI (magnetic resonance imaging) to study auditory systems from a wide range of species and to produce mathematical and three-dimensional computer models of marine animal ears. Check out some amazing images from their lab at:  csi.whoi.edu.

CT Scan performed at the WHOI Computerized Scanning & Imaging Facility
CT Scan performed at the WHOI Computerized Scanning & Imaging Facility

CT scans work by constructing a series of cross-sectional x-ray images of the body as it is passed through a circular gantry. The gantry houses an x-ray tube and a detector assembly, which rotates around the patient. CT scans are particularly good for detecting bone injuries, imaging the lungs and chest, and discerning tumors. The ability to readily produce three dimensional images is a significant advantage of this type of scan versus a regular, two-dimensional x-ray. With respect to diagnosing middle ear disease, CT scans allow us to see the entire middle ear and determine whether it is filled with air (normal) or fluid (infected). Additionally, calculations taken from the scan can tell us the consistency of the fluid in the ear.

On October 23, we brought Townsend to WHOI-CSI for a CT scan. Sadly, the scan confirmed middle ear disease.

We discussed a variety of options including continued treatment, surgery, release without treatment, and euthanasia. Long term treatment including ear flushing and antibiotics hasn’t proven effective at other facilities. Release without treatment could be condemning Townsend to prolonged suffering and eventual death in the wild. We didn’t feel euthanasia was yet warranted because Townsend’s ear disease seemed to be in its initial stages and the animal is otherwise active and in good shape. We felt he would be a good case for surgery.

CT scan performed at the WHOI Computerized Scanning & Imaging Facility.
CT image of the skull showing the normal air-filled tympanic bulla on the right (*), the caseous material in the left (**), and the ruptured ear drum (<<). Note how close the middle ear is to the brain (•). Radiographs are unable to discern the thickness of the bulla, disease of the bone, or often even the presence of fluid or pus in the middle ear of seals. CT scan performed at the WHOI Computerized Scanning & Imaging Facility.

Surgery on any marine mammal is risky, due to their “dive reflex.” Marine mammals are voluntary breathers, meaning when they are unconscious they hold their breath. This makes sense when you realize they spend most of their lives in water and if they breathed while unconscious – like we and other land mammals do – they could wind up with a lung full of water. While this mechanism makes them perfectly adapted to an aquatic lifestyle, it makes it very difficult to put them under anesthesia. Nevertheless, we felt surgery represented Townsend’s best chance of recovery.

To prevent additional infection, we continued daily treatment including flushing Townsend’s ear and applying a broad spectrum topical antibiotic/antifungal/anti-inflammatory medication. And, we began arranging the permissions and assistance we would need to perform surgery.

Last week, we performed a second CT scan to determine whether or not the daily treatments were having any effect and whether or not to proceed with surgery. This scan confirmed the continued presence of middle ear disease.Townsend’s surgery is scheduled for this Wednesday.

To make a donation towards Townsend’s surgery and (hopeful) recovery, please click here.


Many thanks to Dr. Ketten, Julie, and Scott of the WHOI-CSI lab, for their help with Townsend.