We hypothesized that the incidence of recurrence would be higher after LCI than after creation of MDHs and that development of new AHs would not be uncommon during long-term follow-up of dogs with AHs. The secondary objective was to investigate risk factors for recurrence and development of new AHs. The primary objective of the study reported was to evaluate short- and long-term outcomes of surgical creation of MDHs versus LCI for treatment of AHs in dogs, including rates of recurrence at the affected site and development of new AHs. However, there is little information on the incidence of or risk factors for development of new AHs. Although the success rate following surgical treatment of AHs in dogs is high, the cost and invasiveness of surgical treatment may be problematic, especially in dogs requiring multiple surgeries for multiple AHs. Some authors do not recommend LCI because of concerns that it may delay the healing process, 24, 25 but there is little information regarding recurrence rates after LCI. Although LCI is technically easy, inexpensive, and minimally invasive, that study showed that veterinarians who chose LCI were more concerned about recurrence than were those who chose surgery. In a recent survey 22 of veterinary practitioners in the United Kingdom, LCI was the most frequently used first-line treatment for AHs. 23 Reported recurrence rates after these surgeries are low (0% to 27%). 3, 11, 20, 21 These techniques are usually performed in conjunction with procedures intended to decrease the size of the AH cavity, such as application of compression bandages, 1, 10, 18– 21 placement of mattress sutures or stents in the pinna, 1, 10, 19– 22 ablation of the cavity with a carbon dioxide laser, 11 or placement of continuous sutures between the cavity’s walls. 4, 8 Several drainage techniques have been successfully used to facilitate early healing, including placement of a silicone rubber drain 12, 17 or teat cannula, 14 closed-suction drainage, 5, 7, 18 creation of a longitudinal or S-shaped incision, 1, 10, 19 and creation of multiple drainage holes (MDHs). 6, 8 Healing is delayed by fluid accumulation in the cavity, and patients with untreated AHs develop persistent discomfort and, eventually, deformity of the pinna. The disrupted auricular cartilage associated with an AH heals through adhesions resulting from formation of granulation tissue, rather than through cartilage regeneration. This is supported by the therapeutic effect of local corticosteroid injection (LCI) for treatment of AHs. Because the fluid within an AH is actually a seroma rather than a hematoma, 4, 5, 13 the inflammatory response, which might be either the cause or a result of cartilage disruption, may contribute to production of AH fluid. A later study 13 did not support the autoimmune pathogenesis but suggested a role for immunologic factors in cartilage degeneration or healing reactions associated with AHs. Kuwahara 4 postulated, on the basis of results of serologic and immunologic investigations, that cartilage degeneration secondary to an autoimmune reaction was the primary cause of AHs. 1, 6, 8, 10īecause 24% to 64% of dogs with AHs reportedly have no concurrent otitis externa, 9, 11– 14 factors other than mechanical trauma are likely also involved. Ear scratching and head shaking secondary to otitis externa are thought to be the main causes of cartilage disruption, with cartilage disruption leading to rupture of blood vessels in the auricular cartilage and subsequent AH formation. 1– 3 The exact source of this hemorrhagic fluid is unknown however, intraoperative 4– 7 and histologic 4– 6, 8, 9 observations have shown that most AHs in dogs exist within fractures and lacerations of the auricular cartilage. In dogs, aural hematomas (AHs) represent accumulations of hemorrhagic fluid within the layers of the pinna.
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