Aural Hematoma

Aural hematoma is a common surgical condition in small animal practice characterized by the accumulation of blood within the cartilaginous layers of the auricular pinna, typically between the skin and the auricular cartilage. The hematoma forms a fluctuant, often painful swelling on the concave surface of the ear flap, which can vary in size from a small focal nodule to a large, diffuse mass involving the entire pinna. The condition is most frequently seen in dogs, less commonly in cats, and is often associated with underlying ear disease such as otitis externa, allergic dermatitis, or trauma. The hematoma results from shearing forces that rupture the auricular arteries or veins, leading to hemorrhage into the subdermal space. If left untreated, the hematoma may resolve through fibrosis, resulting in a thickened, distorted, 'cauliflower ear' deformity. Surgical intervention is the mainstay of treatment, with various techniques described to drain the hematoma and appose the skin to the cartilage to prevent recurrence and preserve the normal architecture of the pinna.

The exact etiology of aural hematoma is not fully understood, but it is widely accepted that trauma to the pinna, either from direct injury or from vigorous head shaking or ear scratching, is the primary inciting factor. The pinna is a highly vascular structure, with a rich network of arteries and veins lying between the skin and the auricular cartilage. Shearing forces, such as those generated during head shaking, cause the skin to slide over the cartilage, leading to rupture of these vessels and subsequent hemorrhage. Underlying ear conditions that cause pruritus or irritation, such as otitis externa, parasitic infections (e.g., Otodectes cynotis), foreign bodies, or allergic skin disease, are common predisposing factors. In some cases, aural hematoma may occur spontaneously without an obvious cause, particularly in dogs with pendulous ears. Coagulopathies, although rare, can also contribute to the development of hematomas. The condition is more common in dogs with floppy ears, such as Cocker Spaniels, Labrador Retrievers, and Golden Retrievers, but can occur in any breed. In cats, aural hematomas are less frequent and are often associated with ear mite infestations or allergic skin disease.

Aural hematoma is a common condition in dogs, accounting for approximately 0.5% of all canine veterinary visits. It is less common in cats, with a reported incidence of about 0.1%. The condition can occur at any age, but is most frequently seen in middle-aged to older dogs, with a median age of around 6 years. There is no strong sex predilection, although some studies suggest a slight male predominance. Breed predispositions are significant, with pendulous-eared breeds being at higher risk due to the increased mobility of the ear flap. Breeds such as Cocker Spaniels, Springer Spaniels, Labrador Retrievers, Golden Retrievers, and Basset Hounds are overrepresented. In cats, the condition is more common in breeds with large, upright ears, such as the Siamese and Persian, but any breed can be affected. The prevalence of aural hematoma is higher in animals with underlying ear disease, particularly chronic otitis externa, which is present in up to 80% of cases. Seasonal variations have been reported, with a higher incidence in warmer months when otitis externa and allergies are more prevalent.

The pathophysiology of aural hematoma involves a cascade of events initiated by trauma to the pinna. The auricular cartilage is covered by a thin layer of skin on the concave surface, which is loosely attached to the perichondrium. The convex surface has a thicker, more adherent skin layer. The blood supply to the pinna is derived from the great auricular artery, a branch of the carotid artery, which runs along the caudal border of the pinna. The artery gives off multiple branches that penetrate the cartilage and supply the skin. When the ear is subjected to shearing forces, such as during head shaking, the skin and subcutaneous tissues slide over the cartilage, causing rupture of these vessels. The hemorrhage accumulates in the potential space between the skin and the cartilage, forming a hematoma. The hematoma expands as bleeding continues, and the pressure within the hematoma can cause further vessel rupture, leading to a larger hematoma. Over time, the hematoma organizes, with the formation of granulation tissue and fibrosis. If the hematoma is not drained, the fibrotic process can lead to a thickened, distorted pinna, often referred to as 'cauliflower ear'. The presence of a hematoma can also compromise the blood supply to the ear, leading to necrosis of the cartilage in severe cases. In addition, the underlying ear disease that predisposed to the hematoma can worsen, as the hematoma can obstruct the ear canal and exacerbate inflammation.

Several factors predispose animals to the development of aural hematoma. The most significant is the presence of underlying ear disease, particularly otitis externa, which causes pruritus and head shaking. Allergic skin disease, such as atopy or food allergy, is also a common predisposing factor. Ear mite infestations, especially in cats, can cause intense irritation and head shaking. Foreign bodies, such as grass awns, can also trigger the condition. Anatomical factors play a role, as dogs with pendulous ears have a larger, more mobile pinna that is more susceptible to shearing forces. Breed-specific conformational traits, such as a narrow ear canal or excessive hair in the ear canal, can predispose to otitis externa and subsequent hematoma formation. Systemic conditions that affect blood clotting, such as thrombocytopenia or coagulopathies, can increase the risk of hematoma formation. Additionally, trauma to the ear, such as from fights or accidents, can directly cause a hematoma. In some cases, no predisposing factor is identified, and the hematoma appears to occur spontaneously.

The primary clinical sign of aural hematoma is a soft, fluctuant swelling on the concave surface of the pinna. The swelling may be focal or diffuse, and can vary in size from a small nodule to a large mass that distorts the entire ear flap. The affected ear is often painful, and the animal may exhibit signs of discomfort, such as head shaking, ear scratching, or holding the ear to one side. The swelling is typically warm to the touch and may feel tense if the hematoma is under pressure. In chronic cases, the hematoma may become firm due to fibrosis. The overlying skin may appear erythematous or bruised. If the hematoma is large, it can obstruct the ear canal, leading to secondary otitis externa. In addition, the animal may show signs of the underlying ear disease, such as discharge, odor, or erythema of the ear canal. Systemic signs are uncommon unless there is an underlying coagulopathy or severe infection. On physical examination, the hematoma is typically well-circumscribed and fluctuant, and it may be possible to elicit a fluid wave on palpation. The pinna may be thickened and distorted in chronic cases.

The differential diagnoses for aural hematoma include conditions that cause swelling of the pinna or ear canal. These include: 1) Abscess: A purulent collection within the pinna, often secondary to a bite wound or foreign body. It is typically painful, warm, and may have a draining tract. 2) Neoplasia: Tumors of the pinna, such as mast cell tumors, squamous cell carcinoma, or fibrosarcoma, can present as a mass. These are usually firm, may be ulcerated, and are not typically fluctuant. 3) Foreign body: A foreign body, such as a grass awn, can cause localized swelling and inflammation. 4) Cellulitis: Diffuse inflammation of the subcutaneous tissues, often due to bacterial infection, can cause swelling and pain. 5) Seroma: A collection of serum, which is usually non-painful and occurs after trauma or surgery. 6) Cyst: A sebaceous cyst or epidermal inclusion cyst can present as a fluctuant swelling. 7) Hematoma due to coagulopathy: A bleeding disorder can cause spontaneous hematoma formation, which may be bilateral or occur at multiple sites. 8) Ear canal polyp: A polyp in the ear canal can cause swelling and discharge, but is not typically associated with a fluctuant mass on the pinna. 9) Parasitic infection: Severe ear mite infestation can cause inflammation and swelling of the pinna. 10) Trauma: Direct trauma to the ear can cause swelling, but this is usually associated with a history of injury. A thorough history, physical examination, and diagnostic tests such as fine-needle aspiration and imaging can help differentiate these conditions.

The diagnostic approach to aural hematoma is straightforward and typically does not require advanced imaging. The algorithm begins with a thorough history and physical examination. The presence of a fluctuant swelling on the concave surface of the pinna is highly suggestive of aural hematoma. To confirm the diagnosis, fine-needle aspiration of the swelling can be performed; the aspiration of blood confirms the diagnosis. However, aspiration is not always necessary if the clinical signs are classic. After confirming the diagnosis, it is important to identify and address any underlying ear disease. This involves a complete otoscopic examination of the ear canal, which may require sedation or anesthesia. Cytology of ear discharge should be performed to identify bacterial or yeast infections. If a foreign body is suspected, imaging such as radiography or CT may be indicated. In cases where there is no obvious underlying cause, a coagulation profile should be considered to rule out a bleeding disorder. Once the diagnosis is confirmed and underlying causes are addressed, surgical treatment can be planned. The choice of surgical technique depends on the size and location of the hematoma, as well as the surgeon's preference.

Laboratory findings in aural hematoma are generally non-specific and reflect the underlying disease process. A complete blood count may show mild leukocytosis if there is secondary infection or inflammation. Serum biochemistry is usually within normal limits. Coagulation testing, including platelet count, prothrombin time (PT), and activated partial thromboplastin time (aPTT), is recommended if a coagulopathy is suspected, especially in cases with spontaneous or recurrent hematomas. In animals with chronic otitis externa, cytology of ear discharge may reveal bacteria (cocci or rods) or yeast (Malassezia). Culture and sensitivity testing may be indicated if there is a purulent discharge or if the infection is recurrent. In some cases, a fine-needle aspirate of the hematoma may be submitted for cytology to confirm the presence of blood and rule out other causes of swelling. The aspirate typically shows red blood cells, some white blood cells, and occasional macrophages. If the hematoma is chronic, there may be evidence of fibrosis and hemosiderin-laden macrophages.

Imaging is not routinely required for the diagnosis of aural hematoma, as the condition is typically diagnosed based on physical examination and fine-needle aspiration. However, imaging may be useful in certain situations. Radiography of the skull can be performed to evaluate the ear canal for underlying disease, such as chronic otitis media or a foreign body. However, radiography is limited in its ability to visualize soft tissue structures. Ultrasonography can be used to confirm the presence of a fluid-filled cavity within the pinna and to guide aspiration. Computed tomography (CT) provides excellent detail of the ear canal and surrounding structures and may be indicated if there is suspicion of a mass or severe otitis media. Magnetic resonance imaging (MRI) is the imaging modality of choice for evaluating soft tissue structures, including the ear canal and middle ear, and may be useful in complex cases. However, for the majority of aural hematomas, imaging is not necessary, and the diagnosis is made clinically.

Cytology of a fine-needle aspirate from an aural hematoma typically reveals a population of red blood cells, with variable numbers of white blood cells and macrophages. The presence of hemosiderin-laden macrophages may be seen in chronic hematomas. If the hematoma is infected, neutrophils and bacteria may be present. Histopathology is rarely performed on aural hematomas, as the diagnosis is usually straightforward. However, if the hematoma is recurrent or does not respond to treatment, a biopsy may be indicated to rule out an underlying neoplastic process. Histopathology of a chronic hematoma would show fibrosis, granulation tissue, and hemosiderin deposition. In cases where the hematoma is associated with a mass, histopathology would reveal the specific tumor type.

The treatment of aural hematoma is primarily surgical, with the goals of draining the hematoma, preventing recurrence, and preserving the normal appearance of the pinna. Medical management alone, such as aspiration and bandaging, is associated with a high recurrence rate and is not recommended. Several surgical techniques have been described, including: 1) Incision and drainage: A linear or S-shaped incision is made on the concave surface of the pinna, the hematoma is drained, and the skin is sutured to the underlying cartilage using a simple interrupted or mattress suture pattern. This technique is simple but may result in a scar. 2) Teat cannula or drain placement: A small incision is made, and a teat cannula or Penrose drain is placed to allow continuous drainage. The drain is removed after a few days. 3) Multiple stab incisions: Several small stab incisions are made to drain the hematoma, and the skin is sutured to the cartilage with a mattress suture pattern. This technique is less invasive and may result in less scarring. 4) Laser surgery: The use of a CO2 laser to make the incision and coagulate vessels may reduce bleeding and improve visualization. 5) Total ear canal ablation (TECA) and lateral bulla osteotomy (LBO): This is reserved for cases with severe underlying ear disease that is not responsive to medical management. The choice of technique depends on the size and location of the hematoma, as well as the surgeon's preference. Postoperatively, the ear is bandaged to provide compression and prevent recurrence. The bandage is typically left in place for 5-7 days. Systemic antibiotics are not routinely indicated unless there is an underlying infection. Pain management is important, and non-steroidal anti-inflammatory drugs (NSAIDs) or opioids may be used. The underlying ear disease must be treated to prevent recurrence.

The prognosis for aural hematoma is excellent with appropriate surgical treatment. The recurrence rate is low, reported to be less than 10% in most studies. The cosmetic outcome is generally good, although some scarring or thickening of the pinna may occur, especially with larger hematomas. The prognosis is also dependent on the management of the underlying ear disease. If the underlying cause is not addressed, the hematoma may recur. In cases with severe chronic otitis externa, the prognosis for resolution of ear disease is guarded, and long-term medical management or surgical intervention such as TECA may be necessary. Overall, the prognosis for aural hematoma is favorable, and most animals return to normal function and appearance.

Postoperative follow-up for aural hematoma is essential to ensure proper healing and to monitor for recurrence. The bandage is typically removed 5-7 days after surgery, and the incision is evaluated for signs of infection or dehiscence. The sutures are usually removed 10-14 days after surgery. The owner should be instructed to monitor the ear for any signs of swelling, discharge, or pain. The underlying ear disease should be treated according to the veterinarian's recommendations, which may include regular ear cleaning, topical medications, or systemic therapy. A recheck examination is recommended 2-4 weeks after surgery to assess healing and to ensure that the hematoma has not recurred. In cases where the hematoma was associated with chronic otitis, long-term follow-up is necessary to manage the ear disease and prevent recurrence. The owner should be advised to prevent the animal from shaking its head or scratching its ears, which may require the use of an Elizabethan collar or other protective measures.

Clinical pearls: 1) Always evaluate and treat the underlying ear disease to prevent recurrence. 2) When making the incision, be careful to avoid the major blood vessels on the caudal border of the pinna. 3) Use a mattress suture pattern to appose the skin to the cartilage, which helps to obliterate the dead space and prevent re-accumulation of blood. 4) Consider using a teat cannula or drain for large hematomas to allow continuous drainage. 5) Postoperative bandaging is crucial to provide compression and prevent recurrence. 6) In cats, aural hematomas are often associated with ear mites, so treat accordingly. Pitfalls: 1) Failure to address the underlying ear disease can lead to recurrence. 2) Inadequate drainage or failure to obliterate the dead space can result in re-accumulation of blood. 3) Excessive tension on sutures can cause tissue necrosis. 4) Damage to the auricular cartilage can lead to deformity. 5) Postoperative infection can occur if aseptic technique is not maintained. 6) Overlooking a coagulopathy can lead to excessive bleeding and poor outcomes.

Perioperative drug protocols for aural hematoma surgery are based on Plumb's Veterinary Drug Handbook. Preoperatively, prophylactic antibiotics are not routinely recommended unless there is an active infection. If antibiotics are indicated, cefazolin (22 mg/kg IV) can be administered 30 minutes before incision. Postoperatively, pain management is essential. Non-steroidal anti-inflammatory drugs (NSAIDs) such as carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) can be used for 3-5 days. Opioids such as tramadol (2-5 mg/kg PO q8-12h) may be used for more severe pain. If the animal is prone to head shaking, a sedative such as acepromazine (0.01-0.05 mg/kg IV or IM) may be used to reduce activity. Topical ear medications for underlying otitis externa should be used as directed, such as a combination of an antibiotic, antifungal, and corticosteroid (e.g., Otomax, 2-4 drops per ear q12h for 7 days). If a bacterial infection is present, systemic antibiotics based on culture and sensitivity should be used. In cases of chronic otitis, oral corticosteroids such as prednisone (0.5-1 mg/kg PO q24h) may be used to reduce inflammation, but should be tapered. It is important to adjust dosages in animals with hepatic or renal impairment.

The literature on aural hematoma is largely composed of retrospective studies and expert opinion. A landmark study by Kagan (1983) compared different surgical techniques and found that the use of a drain and suture apposition resulted in lower recurrence rates compared to simple drainage. A more recent study by Parnell et al. (2017) evaluated the use of a CO2 laser for aural hematoma surgery and found it to be safe and effective, with good cosmetic outcomes. The importance of treating underlying ear disease is emphasized in multiple studies, with recurrence rates as high as 50% if the underlying cause is not addressed. A consensus statement from the American College of Veterinary Surgeons (ACVS) recommends surgical drainage and apposition of the skin to the cartilage as the treatment of choice. There is no evidence to support the use of medical management alone, as it is associated with high recurrence rates. Overall, the evidence supports surgical intervention with attention to underlying causes for the best outcomes.