Osteomyelitis of the hyoid bones in two calves
© Nuss et al. 2015
Received: 17 April 2015
Accepted: 21 August 2015
Published: 22 September 2015
Two calves were referred because of ptyalism and difficulty opening the mouth (Calf 1) and for elective umbilical hernia surgery under inhalation anaesthesia (Calf 2). Additional clinical signs were increased breath sounds and swelling in the region of the mandibular angle in Calf 1. Ultrasonography and endoscopy revealed oral inflammation and abscessation in the area of the base of the tongue in both calves. Infection of the hyoid apparatus was suspected based on ultrasonographic findings and confirmed by means of computed tomography. In Calf 1, there was no response to treatment with systemic antibiotics, nonsteroidal anti-inflammatory drugs and local lavage, and Calf 2 was not treated. Both calves were euthanized because of a poor prognosis and the diagnoses confirmed during postmortem examination. In Calf 1, the abscess was associated with complete destruction of the left epihyoid bone and partial destruction of the left stylohyoid and ceratohyoid bones. In Calf 2, the abscess was located at the distal end of the right stylohyoid bone near the epihyoid bone. Stomatitis or laryngeal and pharyngeal abscessation caused by sharp feed particles are common in cattle and infection of the hyoid apparatus should be included in the differential diagnosis.
Mechanical dysphagia in calves is predominantly caused by diffuse inflammatory processes or abscesses that result from foreign bodies or injuries from rough feed particles; the tongue and larynx are most commonly affected . Injuries of the oropharynx and larynx are associated with considerable inflammation of the upper neck region, swelling, and abnormal respiratory noises [2, 3]. Clinical, ultrasonographic, radiographic, or endoscopic examinations may identify the nature of the swelling [1, 4, 5] and in some cases allow targeted treatment. To our knowledge, involvement of the stylohyoid bone in infectious inflammatory conditions of the oral cavity in cattle has not been described but osteopathies or fractures of the stylohyoid bone are common in horses [6–10]. The hyoid apparatus plays a crucial role in the swallowing process by moving the food bolus over the larynx. The hyoid body, which is seated between the larynx and the tongue, consists of the basihyoid and the paired thyrohyoid and ceratohyoid bones. Two branches of the hyoid apparatus function as suspension for the body and consist, from distal to proximal, of the paired epihyoid, stylohyoid and tympanohyoid bones . Diseases of the stylohyoid bones in adult horses are referred to as temporohyoid osteoarthropathy because of their typical localization and nature. This condition may involve the middle ear, the temporohyoid joint, the stylohyoid bone and the petrous portion of the temporal bone. Possible aetiologies discussed in the literature include extension of infection from otitis media or interna, guttural pouch infection, strangles, trauma and osteoarthritis [6–10]. Clinical signs include chronic weight loss, nasal discharge when the guttural pouch is affected, paralysis of the tongue and locked jaw, and the prognosis is unfavourable. Temporohyoid osteoarthropathy is accompanied by bony proliferation and fusion of the temporohyoid joint. The restriction of mobility is believed to lead to stress fractures of the petrous temporal and/or stylohyoid bones.
Calf 1 was a 6-month-old Brown Swiss heifer calf with a 3-week history of anorexia, ptyalism and swelling of the throat region. Examination of the oral cavity by the referring veterinarian revealed an injury in the region of the left mandibular angle. The calf was treated with an analgesic (meloxicam) and an antibiotic (spiramycin), but did not respond to treatment and was referred to the Department of Farm Animals, Vetsuisse Faculty. Calf 2 was a 3-month-old Holstein–Friesian heifer calf referred for elective umbilical hernia surgery. No other abnormalities were reported and the calf appeared healthy on clinical examination except for increased breath sounds.
Among the clinical signs observed in Calf 1, difficulty opening the mouth was of particular interest because this was a characteristic finding in horses with infected stylohyoid bone fracture . It is likely that the bony proliferations of the mandibular and stylohyoid bones and the inflammation contributed to the inability of the calf to open its mouth completely. Infection of the hyoid apparatus in both calves was probably caused by feed particles that were forced caudally during swallowing and perforated the pharyngeal mucosa. The organisms isolated are oral commensals and colonise lesions following traumatic damage of the overlying mucosa. Trueperella pyogenes in particular is a common opportunistic pathogen in cattle, and F. necrophorum and Bacteroides spp. are recognised as important primary pathogens, causing oral and laryngeal necrobacillosis .
The distal portion of the stylohyoid bones and the epihyoid bones are the structures of the hyoid apparatus  closest to the oro-pharyngeal mucosa and thus the most likely bones to be involved in an oro-pharyngeal infection. Another possibility is the spread of an infection from the palatine tonsil since the inflammation was located in this area in Calf 2. In the calves reported here, it is conceivable that the infection started at the cartilaginous articulations and then spread to the epihyoid and stylohyoid bones. Osteolytic changes of the ceratohyoid bone have also been described in horses although usually the articulation between the stylohyoid and temporal bones is affected [7, 10], occasionally accompanied by middle ear infection . However, there was no evidence of otitis externa in the calves reported here and CT scans did not show inner or middle ear abnormalities. Surgical treatment of osteomyelitis of the hyoid bones was not considered feasible because of the location of the lesion and the destructive changes seen in CT image reconstruction. Furthermore, functional impairment of the hyoid apparatus would be expected after any form of treatment and therefore both calves were euthanized. One report of successful surgical treatment of a stylohyoid bone fracture associated with an abscess in a horse has been published but a description of the surgical technique was not provided .
In summary, in calves with swellings in the throat and mandibular area, particularly in association with difficulty opening the mouth, disorders of the hyoid apparatus should be included as a differential. The diagnosis can be confirmed by means of ultrasonography and CT. Although the latter is not an absolute prerequisite for a definitive diagnosis, it allows precise characterization of the disease process and the involvement of bony structures.
KN prepared the manuscript, UB and KN supervised the clinical examination, EM examined the calves and performed the ultrasonographic examination. Radiography and CT were evaluated by FW, supervised by PK. Anaesthesia was provided by SR and post-mortem examination by AJM. All authors read and approved the final manuscript.
The authors thank Dr. M. Bachmann, Schlieren, and Dr. Giuliani-Rupp, Tscherlach for referring the calves.
Compliance with ethical guidelines
Competing interests The authors declare that they have no competing interests.
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