dog ear infection anatomy and physiology

Dog ear infections can be confusing because the dogs ear is actually mostly hidden.  Dog ear infections often occur deep within the ear, and dogs may have painful ears with pus or blood discharge for days before you notice any problems.

Learning the anatomy of the dogs ear and how this relates to infection, applying medication like ear drops and cleaning the ear is essential to successful treatment.

Dog Ear Vet

Read more about symptoms of dog ear infections

Read more about otitis externa anatomy

Otitis externa 
Introduction 
Otitis externa, or inflammation of the external ear canal, is a common condition in dogs. It is characterized by inflammation of the soft tissue components of the external ear canal and is particularly prevalent in dogs with long, floppy ears. Otitis externa may affect 20 percent of dogs. 
  
Left: as demonstrated by the above ear-model, the ear canal has a vertical and a horizontal component. This predisposes the dog to ear infections as debris must work its way upward rather than straight out. 
Right: otitis externa with brown exudate 
Anatomy of the ear 
The ear of the dog and the cat is composed of three parts: the external ear, the middle ear and the inner ear. Together these components allow the animal to locate a sound and the direction from which it emanates, to orientate the head in relation to gravity and to measure acceleration and rotation of the head. 
Selective breeding, of dogs in particular, has resulted in a wide variation in relative size and shape of the components of the external ear. Compare, for example, the French Bulldog, the Cocker Spaniel, the German Sheperd Dog, the St. Bernard and the Persian cat. The pinnal shape and carriage, the diameter of the external ear canal, the degree of hair and amount of soft tissue within the external ear canal, and the shape of the skull within which the middle and inner ear lie vary from one breed to another. 
The external ear canal 
An importrant difference between the tissues of healthy ears and infected ears is the appaerance and distribution of the glandular structures. In a healthy ear, sebaceous glands are usually numerous , large and actively secreting. In chronic otitis externa, they are less active and much smaller. The external ear canal may normally contain a small amount of wax that is yellowish-brown in color. 
Signs of ear disease
Every day we see dogs who have problems with their ears. Signs of these ear problems include: 
• Odor 
• Scratching or rubbing of ears and head 
• Discharge in the ears 
• Redness or swelling of the ear flap or canal 
• Shaking of the head or tilting it to one side 
• Pain around the ears 
• Changes in behavior such as depression or irritability 
Causes of ear disease 
• Allergies such as atopy or food allergies 
• Parasites - ear mites. Adult mites are large, white and free-moving. the life cycle of the ear mite is three weeks. Mites are characterized by thick, reddish-brown or darkbrown exsudate and crusts in the ear. Ear mites are the single most frequent cause of otitis externa in the cat. Mites are highly contagious. 
• Bacteria and Yeast infections. Staphylococcus or Streptococcus (Gram-positive bacteria) infections are most frequently associated with acute otitis externa. There is a light-brown, creamy exudate. Gram-negative organisms (Proteus, Pseudomonas, E.Coli) are most frequently observed in chronic otitis externa or recurrent ear disease. There is a yellow exudate. Malassezia canis is a budding yeast: a brown, waxy adherent exudate. 
• Ticks. The spinous ear tick is found in the external ear canal of dogs and cats. The ear canal become packed with immature ticks. Treatment involves mechanical removal, spraying or dipping the coat with an insecticide. 
• Foreign bodies, e.g., plant awns 
• Trauma 
• Hormonal abnormalities, e.g., hypothyroidism 
• The ear environment, e.g., excess moisture and ear anatomy 
• Hereditary or immune conditions 
• Tumors 
Treatment 
The first step in otitis externa is a thorough cleansing of the ear canal followed with irrigation of the canal with a warm antiseptic solution (chlorhexidine or betadine). A warm sterile solution should be used if there is any indication of ruptured membrane. 
Most topical ear medications are combinations containing one ore more antiparasitics, antibacterial, antimycotic, anti-inflammatory, local anesthetic, ceruminolytic and drying and cleaning agents. Oil or ointment bases help moisturize the skin and are effective in dry, scaly or crusty lesions. Solutions or lotions are most frequently used in exsudative ear lesions. 
Cotton applicator swabs can be used to clean the inside of the earflap and the part of the ear canal you can see. They should NOT be used farther down in the ear canal since that tends to pack debris in the ear canal, rather than removing it! 
Chronic otitis externa is usually associated with underlying skin conditions such as seborrhea, hypothyroidism or improperly or neglected ear disease.ar problems caused by a systemic disease such as a hormone abnormality or allergy must include a therapy that treats the whole dog, such as hormonal replacement or allergy testing and hyposensitization (immunotherapy). 
Surgical treatment
Depending on the severity of the problem, the vertical canal may need to be opened surgically. This enables debris to be removed more effectively. This is done to prevent severe scarring after prolonged specific medical therapy has been ineffective. This procedure is called a lateral ear resection, Zepp procedure, or LaCroix procedure.  
If the canal becomes so scarred that it is practically closed, ablation may be the final option. In this surgical procedure, the entire ear canal is removed and healthy tissue is allowed to grow in. This procedure is a last resort after severe infection has made effective medical treatment impossible. A specialist is called in for these cases and although surgery is expensive, dogs with chronic severe otitis usually require no further ear treatment for the rest of their lives. 

 
Aural hematoma 

Complication of ear disease: aural hematoma 
When a dog with uncomfortable ears shakes and scratches vigorously, a blood vessel in the ear flap may rupture.  This leads to bleeding into the tissues of the pinna (see above illustration). The usual recommendation is to have the blood clots removed and the ear bandaged and cleaned under anesthesia. If the hematoma is not so big as to occlude the ear canal (thus preventing medication), the option to forgo surgery exists; but without surgery, the ear may scar down into an abnormal appearance. 
Preventing ear disease
The key to healthy ears is to keep them clean. Check your dog’s ears weekly. A slight amount of waxy buildup may be present in normal ears. If your dog swims a lot, has pendulous ears, or a history of ear disease, routine cleaning (often once to three times per week) is recommended. Use the same procedure as described above. Excess hair around the ear can be clipped to allow more air flow. Treat any underlying condition that predisposes your dog to ear problems. 
Remember, if your dog is showing severe discomfort, the ears have a bad smell, or the ear canals look very abnormal, do not delay in contacting your veterinarian. If your dog has a ruptured or weakened eardrum, some ear cleansers and medications could do more harm than good.