Acute upper airway obstruction due to retropharyngeal hematoma in a dog with Anaplasma species: a case study

An 18-month-old, intact female water spaniel (16 kg) was referred to the Veterinary Teaching Hospital, University of Extremadura, after experiencing weakness, neck pain and progressive paralysis in all limbs that led to lateral recumbency for 7 days. There were no other remarkable findings on physical examination. Complete blood count and serum biochemistry profiles revealed leukocytosis (white blood cell count: 31.5 × 10⁹/L; reference range, 5.9–16. 6 × 10⁹/L); elevated alanine aminotransferase (377 IU/L; reference range, 15–52 IU/L) and alkaline phosphatase (317 IU/L; reference range, 20–70 IU/L); and thrombocytopenia (109 × 10⁹/L; reference range, 117–460 × 10⁹/L). No coagulation testing was performed.

Based on the history and examination findings, possible differential diagnoses included meningitis, polyradiculoneuritis, polymyositis, and discospondylitis. We anesthetized the dog for a cisternal puncture and cerebrospinal fluid (CSF) tap and encountered no complications during the procedure. Analysis of the cerebrospinal fluid showed elevated protein (15 g/L; reference range, < 0.25 g/L) and neutrophilic pleocytosis (white blood cell count, 5.0 × 10⁹/L; reference range < 5 × 10⁶/L; 69 % neutrophils, 39 % lymphocytes). Based on these results, and pending CSF culture, there was a suspicion of bacterial meningitis and the dog was started on antibiotic therapy (sulfamethoxazole-trimethoprim,¹ 15 mg/kg PO q 12 h and clindamycin,² 10 mg/kg PO q 12 h).

Five hours after extubation, the dog developed stridor and evidence of upper airway obstruction that worsened rapidly. The dog was agitated, tachypneic and cyanotic on room air and was immediately transferred to the operating room to secure the airway. Intubation was attempted via direct visualization with laryngoscopy, but this was difficult because of the size of the hematoma. The epiglottis was not visualized and the correct position of the endotracheal tube was confirmed using capnography. On examination of the oral cavity and oropharynx, there was an ecchymotic swelling of the soft palate. Laryngoscopy confirmed extensive hematoma; pharyngoscopy demonstrated a soft, bulging, violaceous mass involving the lateral and dorsal pharyngeal walls (Fig. 1). A lateral cervical radiograph revealed marked prevertebral soft tissue swelling (Fig. 2). The dog was then transferred to the magnetic resonance imaging (MRI) unit under general anesthesia, and urgent MRI³ of the neck was performed (Fig. 3). MRI revealed a retropharyngeal mass with features consistent with hemorrhage; the trachea was outlined only by the endotracheal tube and the mass was causing dorsal compression of the airway.

The severe extent of the upper airway obstruction necessitated surgical tracheostomy, which was performed uneventfully, and aminocaproic acid⁴ (20 mg/kg IV), vitamin K⁵ (2 mg/kg IV), and ethamsylate⁶ (12.5 mg/kg IV) were administered. Once the dog was stabilized, blood tests were repeated. Hemoglobin was 109 g/L from 123 g/L, platelet count was 36 × 10⁹/L from 109 × 10⁹/L, and clotting study results were in the normal range (thrombin time: 6.4 s, reference range: 6–9 s; partial thromboplastin time: 5.1 s, reference range: 5.1–7.9 s; prothrombin time: 8.7 s, reference range: 8.6–12.9 s). Despite thrombocytopenia that was just above the range to cause bleeding, buccal mucosal bleeding time was normal (2 min; reference range, 1.7–4.4 min); platelet aggregometry was not performed to assess platelet function. Anaplasma and Ehrlichia blood antigen detection (4DX⁷) was performed, and the dog tested positive for Anaplasma spp.; therefore, prednisone⁸ (2 mg/kg IV q 12 h) and doxycycline⁹ (10 mg/kg PO q 24 h) were initiated as treatment for rickettsial meningitis. Over the next 24 h, the platelet count increased to 153 × 10⁹/L and the hemoglobin concentration stabilized at 109 g/L. The tracheostomy tube was removed on the fourth day and normalization of the prevertebral soft tissue was noted on a lateral cervical spine radiograph (Fig. 2). Based on the clinical and radiological findings, a diagnosis of RH was made. Following negative CSF culture, antibiotic therapy was reduced to doxycycline for one month. Rehabilitation therapy was instituted and in 7 days the dog was able to rise and take a few steps alone. The neurological signs improved with treatment and resolved over the next several months resulting in complete and uneventful recovery.

In this case, a flexible laryngoscope confirmed the diagnosis. The role of flexible pharyngoscopy cannot be overemphasized. Even a small bulging of the posterior wall of the pharynx should alert clinicians and guide the clinical strategy towards a high suspicion of a retropharyngeal space-occupying lesion [18]. Computed tomography is also important to confirm the diagnosis and to assess the extent of the hematoma and its relation to structures in the neck [6]. MRI offers several advantages over computed tomography regarding multiplanar anatomic display and superior soft tissue contrast, allowing more specific diagnoses to be made [19]. MRI not only better depicts the extent of retropharyngeal lesions but, most importantly, is able to identify acute and subacute blood products, thereby affecting both diagnosis and management. MRI is sensitive to blood products in different stages of evolution because of their paramagnetic signal properties, which change over time depending on the dominant component (e.g., acute deoxyhemoglobin, subacute intra- or extracellular methemoglobin, and chronic hemicromes).

Spontaneous bleeding generally does not occur until platelet counts fall below 20–50 × 10⁹/L unless a concomitant bleeding disorder exists, in which case it can be a life-threatening event. Thrombocytopenia does not always require intervention, but it certainly warrants monitoring and attention to prevent bleeding episodes [20]. In this case, the dog responded well to treatment with doxycycline and platelet transfusion was not necessary.

In human medicine, most authors report conservative treatment for successful management of RH, and the condition usually resolves within several weeks [6]. Treatment depends on the size, location, and clinical evolution of the patient. In small hematomas, treatment tends to be conservative, and spontaneous resolution occurs [21]. Immediate opening of the hematoma for aspiration appears to increase the risk of infection, which often extends to the mediastinum. If the hematoma is large and re-absorption unlikely, or if the hematoma has extended rapidly, surgical evacuation and controlling the source of bleeding is indicated once the patient has been stabilized [13]. Late complications include a non-resolving hematoma or abscess formation.

There is little consensus in the literature regarding the use of steroids or prophylactic antibiotics in patients with RH [2] and the use of systemic steroids is controversial. Hemorrhage in the upper airway dissects along multiple fascial planes, and this incites an inflammatory reaction that is limited by the use of steroids. Although not of proven benefit, systemic steroids have been used in numerous case reports of upper airway hematomas in people [22, 23].