Domoic Acid toxicosis is primarily identified in California sea lions. It affects humans so there is a lot of interest in the condition and a lot of ongoing research. We will have more detailed information for this disease posted soon including gross necropsy and histologic specimens, however in the meantime we offer this brief explanation.

Domoic acid is a glutamate analog which, following ingestion, results in hyperexcitation of specific receptors in the brain. The hyperexcitation results in seizure activity in the short term and behavior changes and intermittent seizures in the long term. Long term cases develop hippocampal atrophy as a result of the cellular damage and subsequent cell death.

In a T2W sequence the CSF is bright or white, and white matter is slightly darker then gray matter in the brain. Depending on the acquisition method, fat may be an intermediate or bright signal intensity. The T2W transverse image of the brain below demonstrates hippocampal atrophy of the right side of the hippocampus (on the left of the image, blue circles indicate the hippocampus). In a clinical case, atrophy needs to be identified on least 3 consecutive images  and multiple series to have confidence in the diagnosis. Mild positional asymmetry is also evident in this image and can complicate the interpretation. A localizer image has been included to illustrate the orientation of the transverse image. The movie underneath demonstrates a T2W MRI sequence of most of the brain including the hippocampal region for the same animal as represented by the single image. Press play and the movie will scroll through automatically.

Below is a T2W transverse image through the head of a pilot whale that stranded dead. Some of the superficial tissues were trimmed in order to fit the head into the coil in the scanner. The image shows hyperintensity (bright signal) within the left maxillary sinus (on the right side of the image). Compare this to the normal, contralateral, air-filled sinus which appears black. The signal in the abnormal sinus is similar to the signal from the CSF within the ventricles thus is consistent with fluid. The type of fluid cannot be definitively characterized from this one image, but differentials include transudate or hemorrhage. On necropsy examination, Nasitremma sinusitis was diagnosed. This demonstrates the use of MRI to aid diagnosis of disease by directing the focus of the necropsy.

T2W midline sagittal image of the same brain shown in the above transverse image. The green lines indicate the orientation of the transverse image. The main parts of the brain can be clearly seen on this image - cerebrum, cerebellum, pons, medulla.

SINUSITIS IN A PILOT WHALE Globicephala melas

NORMAL                     ABNORMAL