Case report: Evaluation of head trauma in a tawny owl (Strix aluco) with advanced imaging diagnostic, FVEP and BAER test

Abstract

An adult pet tawny owl (Strix aluco) presented to a veterinary hospital at Parma University with a history of head trauma. After a critical care protocol including thermal, oxygen and fluid support aimed at stabilizing the patient, a neurological examination was performed. During neurological evaluation, marked lethargy and an inability to rise from a recumbent position was noted. Anisocoria was also present, with a mydriatic left pupil exhibiting no pupillary light response (PLR) even on direct illumination of both eyes. On ocular fundus examination, retinal hemorrhage and retinal detachment were observed. Based on these clinical findings, a complete work-up was performed, including hematological exams and total body X-ray studies followed by a computed tomography (CT) scan. Additional examinations, such as brainstem auditory evoked response (BAER) measurement and flash visual evoked potential (FVEP) recording, were performed. FVEP measurements performed on the left eye exhibited no peaks in either series of stimulations, indicating an altered functional integration within the visual pathway. A CT scan revealed a large hypoattenuating lesion within the right cerebral hemisphere, suspected to be intraparenchymal edema. The BAER test demonstrated an altered trace consistent with brainstem involvement and left hypoacusis due to cranial nerve VIII deficiency. Head trauma can result in significant neurological impairments in birds, impacting their behavior, mobility, and cognitive abilities. FVEP recordings, BAER tests and CT scans may be useful diagnostic tools in clinical practice. Understanding the causes and neurologic presentation of avian traumas is essential for effective prevention, diagnosis and treatment of affected birds.

Keywords: BAER; FVEP; advanced imaging; birds of prey; head trauma; raptors; tawny owl.

Figure 1

Fundus inspection of the left (A) and right eyes (B). (A) Vitreal hemorrhage (black arrow) and retinal detachment (white asterisk) are visible. (B) Normal fundus appearance.

Figure 2

Coronal plane image with soft tissue algorithm in the brain window. Scale bar = 8 mm. A hypoattenuating ovalar intra-axial lesion with ill-defined margin is observed at level of parieto-temporal area at the level of the right cerebral hemisphere (white arrow) (Pitch 0.562, slice thickness: 1.25 mm).

Figure 3

Flash visual evoked potentials of the right eye (A) and left eye (B). Traces a and c were obtained by light stimulation with the eyes open. Traces b and d were obtained with the eyes closed. The recorded traces from the left eye exhibited pathological findings, demonstrating the absence of peaks in both stimulations. Conversely, the traces obtained from the right eye were normal and exhibited the expected peaks.

Figure 4

(A) Brainstem auditory evoked response (BAER) tests of the left ear (A) and the right ear (b). Both recorded tracings exhibited a complete absence of waves III to V, suggesting a likely overall involvement of the brainstem structures, as indicated by the clinical evaluation. However, on the left side (a), there is probable involvement of the inner ear. This hearing impairment resulted in the disappearance of wave I (cranial nerve VIII) and subsequent waves in the recordings. (B) Left (c) and right (d) BAER tracks of a clinically healthy tawny owl (Strix aluco) used to compare the BAER tracks obtained from the patient. The presence of five physiological waves (I–V) is evident.