Infestation of the pterygoid air sinuses of dolphins by flukes (Nasitrema sp) is a common, perhaps universal event in the western Gulf of Mexico. This is potentially an important morbidity factor as the air sinuses have an intimate and close connection to the tympanic bullae and the acoustic nerves. In some species, under some circumstances, sinus infestation is associated with concomitant invasion of the brain by flukes. While the effect of the parasite in the brain is well described, its effect in the air sinus is not.

Our necropsy procedure involves inspection of the air sinuses in every animal, and lately, histological sampling of the sinus mucosa whether apparently normal or not. We have examined the sinuses of 9 cetacean species by inspection, and supported inspection with histologic evaluation of the effect of parasitic infestation on the tissues of the pterygoid sinus in 22 bottlenose dolphins (Tursiops tmucahls), 1 rough-tooth dolphin (Steno bredanensis), 1 beaked whale (Mesoplodon europaeus), and 1 striped dolphin (Stenella ceruleoalba). Only 3 T. truncatus, all young animals, had no grossly identifiable sinus parasites. Prolonged infestation is commonly associated with production of a bloody, brown to black mucoid secretion, grossly visible ulcers, and patches of white epithelium. As the sinuses are directly in continuity with the tympanic bullae, it is common to find flukes in the center of a bulla as well as in the sinus. Although a tympanic bulla was eroded and weakened in one T. truncatus, and the bone surrounding the ossicle eroded in another, we have never observed penetration of the calvarium in T. truncatus while we have found brain lesions with ova in two species of Stenella. In one T. truncatus, both Nasitrema and a nematode resembling lung worm were found in the sinuses.

In T. truncatus while it is not entirely worked out, the normal sinus mucosa appears to vary with the region of the sinus. In some areas, it consists of a respiratory columnar epithelium over a relatively loose connective tissue stroma containing large blood vessels. In other areas, squamous epithelium overlays deep, complexly branching mucous glands. Infestation with flukes, which burrow into gland necks and are retained by backward-directed cuticular spines, results in erosion of epithelium, with inflammation of variable intensity. Ulceration and bleeding are common, and the appearance of a different pattern of squamous epithelium suggests that squamous metaplasia is a common response to prolonged mucosal irritation. In the one Steno examined histologically, trematode ova were found embedded in the superficial submucosa, with absent inflammation and intact surface epithelium. This suggests that in this species, parasites may be eliminated and the lesion healed.