Ear Surgery: Practical Tips for Success and Complication Avoidance

Surgery of the ear is commonly indicated in small animal practice for a variety of causes including otitis externa, otitis media as well as traumatic and neoplastic conditions of the bulla, ear canal and pinna. The complexity of these interventions can range from very basic to highly complex and ear surgery remains an area of soft tissue surgery that is associated with significant morbidity. In order to perform some of the more advanced surgeries an in depth knowledge of regional anatomy is vital. The cartilaginous ear canal is made up of the pinna, which is supported by the auricular cartilage. The pinna is continuous with the vertical canal, which then becomes more perpendicular to the skull base and continues as the horizontal canal. The annular cartilage fuses with the auricular cartilage but during dissection of the ear canal an obvious step can be appreciated between these two cartilages. The annular cartilage attaches to the skull at the external acoustic meatus, which forms the entrance to the tympanic bulla and is the insertion site of the tympanic membrane. The arterial supply to the external ear comes from a branch of the external carotid artery and venous blood drains to the maxillary vein. The retroarticular vein lies just rostral to the external auditory meatus and can easily be damaged during dissection. When this occurs it can be challenging to grasp and cauterize or ligate the vessel due to limited accessibility. Sustained packing of the area in combination with placement of a topical hemostatic agent such as an absorbable gelatin sponge is usually successful in stopping the hemorrhage. Several important neurological structures lie within the surgical field especially when total ear canal ablation is performed and neurological complications are the most common group of complications associated with ear surgery. Axons from postganglionic sympathetic neurons course close to the wall of the middle ear in dogs and cats and are particularly exposed in cats during curettage of the tympanic bulla during TECA-BO surgery. Damage to these fibers can result in Horners syndrome. The facial nerve exits the stylomastoid foramen immediately caudal to the external auditory meatus and then travels ventrally and cranially around the aspect of the tympanic bulla. The entrance to the inner ear at the epitympanic recess lies on the dorsomedial aspect of the tympanic bulla. Signs of vestibular disease can result in damage to the structures of the inner ear if over-exuberant curretage occurs in this area or if a fracture is propagated into the this area during bulla osteotomy. It is important to remember that unlike dogs who in general have one compartment to the bulla, the feline tympanic cavity consists of two compartments, a larger ventromedial and a smaller craniolateral compartment which are separated by a bony septum. It is imperative to penetrate both cavities of the bulla in cats as disease is usually not limited to one cavity.