Abstract

Techniques of standard radiography, computed tomography, and contrast radiography were systematically applied to postmortem skull and casques of representative species of the hornbill family. Skeletal preparations were completed of these specimens for direct examination. Diagnostic images and photographs were evaluated to document internal casque anatomy.

Introduction

The unique features of the family Bucerotidae include a casque, or ornamentation on the dorsal maxillary beak. Each of the 54 extant hornbill species has a different shape, size, and coloration of casque that may be as simple as a ridge or as elaborate as a recurved horn. The casque is essentially an air-filled cavity enclosed by minimal bone, except in one species (greater helmeted hornbill, Buceros vigil).^2-4 A horny keratin overlies the casque and produces the bulk of its visible mass. It originates from a highly vascular ridge of the maxillary rhamphotheca in the juvenile. Progressively enlarging until sexual maturity, a different casque contour is produced by each gender, with males generally having larger, more elaborate structures than the females. Detailed descriptions of the external appearance are available, but little information is available about the internal anatomy.^2,3 The clinical challenge of a structure poorly described has become apparent with the hornbill casque (personal communications: T. McNamara, 2000; G. Pirie, 2003).^6,7 The casque is subject to self-induced trauma, conspecific injury, environmental damage, and neoplasia (personal communications: R. Aguilar, 2003; T. McNamara, 2000; K. Petrini, 2000; G. Pirie, 2003; R. Wagner, 2001).^5,7,8 Surgical exploration, resolution of disease, and reconstruction of this area would be improved by anatomic knowledge.

To date, evaluation of the casque has been essentially through standard radiography. Although multiple views have assisted with assessment of disease, they have not substantially advanced the anatomic knowledge of the structure. In domestic animal medicine, computed tomography (CT) has been utilized for imaging the nasal planum, nasal sinuses, and surrounding tissues.^1,6 Furthermore, traditional radiography has been expanded in domestic species by contrast techniques. These techniques were systematically applied to advance clinical understanding of the Bucerotid casque anatomy. Specifically, the interconnections of the casque space with the sinuses, the nares themselves, and the oropharynx may vary by species (K. Petrini, personal communication, 2000).^3,4

Methods

By an addendum to the established necropsy protocol of the Coraciiformes Taxon Advisory Group (TAG), seven specimens were obtained for evaluation: silvery-cheeked (Bycanistes brevis) (female), trumpeter (Bycanistes bucinator) (female), rhino (Buceros rhinoceros) (male), wreathed (Rhyticeros undulatus) (female), greater Indian (Buceros bicornis) (female), wrinkled (Aceros corrugatus) (male and female), and Jackson’s (Tockus deckeni) (male).

The intact skull and casque were maintained frozen until thawed for imaging. Standard radiography (right lateral, left lateral, ventrodorsal, dorsoventral, and skyline-rostrocaudal) was completed, then the specimen was shipped on ice for CT imaging (Texas A&M University College of Veterinary Medicine, College Station, TX, USA) in standard positioning (lateral and ventral recumbency) for a clinical avian patient. Both sagittal and craniocaudal sectioning was performed at 2–5-mm slice thickness, depending on size of the specimen. The specimen was then returned on ice for the contrast radiography. The casque internal space was estimated by multiplication of linear measure (in mm) of the casque (height, length, width) from the plain films. This calculated volume (in ml) of radio-opaque contrast media (RenoCal 76, 37% organic bound iodine, Bracco Dx, Princeton, NJ, USA) was instilled into the casque and the standard radiographic series repeated. Professional preparation (Skulls Unlimited, Oklahoma City, OK, USA) of the skull and casque was performed, and specimens were sectioned sagittally to allow access to the interior of the casque and skull.

Results and Discussion

Diagnostic images were evaluated for internal casque anatomy (dimensions, contour, shape, and interconnections to sinuses within the skull and beak). The skeletal preparations were directly examined and photographed to document anatomic features. The images and skull preparations were compared directly, then considered between the genera, the species, and genders.

This assembled data is interpreted for clinical applications. Utility of the casque interior as a depot for pharmaceutics, including antibiotics and antineoplastics, may be considered. Surgical approaches and limits to the casque, skull, and sinus are available from the TAG veterinary advisor. Continued documentation to obtain similar image studies from the originally selected 12 hornbill species as representatives of the captive population is ongoing.

Acknowledgments

Funding for this endeavor was provided by a generous grant (in-kind) from the Schubot Center for Avian Medicine, Texas A&M University, College Station, Texas, and through annual research funding from the Association of Avian Veterinarians. I appreciate the submitted specimens from the following institutions: Audubon Institute, New Orleans, Louisiana; Chaffee Zoo, Fresno, California; Dallas Zoo and Aquarium at Fair Park, Dallas, Texas; San Antonio Zoological Gardens, San Antonio, Texas; and Wildlife Conservation Society, Bronx, New York. I thank Chris Sheppard, PhD, Coraciiformes TAG chair, and the entire Coraciiformes TAG for their steadfast support of the endeavors of their veterinary advisor.

Literature Cited

1.  Assheurer, J. 1997. MRI and CT Atlas of the Dog. Blackwell Wissenschaft, Berlin, Germany. Pp. 1, 44–47.

2.  Kemp, A.C. 2001. Family Bucerotidae (hornbills). In: del Hoyo, J., A. Elliott, and J. Sargatal (eds.). Handbook of the Birds of the World, Volume 6 (Mousebirds to Hornbills). Lynx Edicons, Barcelona, Spain. Pp. 448–451,488–523.

3.  Kemp, A. 1995. The Hornbills. Oxford University Press, New York, NY. Pp. 19–22.

4.  Manger Cats-Kuenen, C.S.W. 1961. Casque and bill of Rhinoplax vigil (Forst.) in connection with the architecture of the skull. Verh. Kon. Ned. Akad. Wet., Afd. Natuurkel, NV Noord-Holland Uitgev. Maatschappij Amersterdam. Pp. 1–47.

5.  Miller, R.E., D.W. Trampel, W.J. Boever, and M.A. Kling. 1985. Carcinoma in the casque of a greater Indian hornbill (Buceros bicornis). J. Zoo. Anim. Med. 16: 131–136.

6.  Moore, M.P., P.R. Gavin, S.L. Kraft, C.E. DeHaan, C.W. Leather, and R.V. Dorn. 1991. MR, CT, and clinical features from four dogs with nasal tumors involving the rostral cerebrum. Vet. Radiol. 32: 19–25.

7.  Suedmeyer, W.K., D. McCaw, and S. Turnquist. 2001. Attempted photodynamic therapy of squamous cell carcinoma in the casque of a greater hornbill (Buceros bicornis). J. Av. Med. Surg. 15: 44–49.

8.  Wünschmann, A., M.J. Weisman, J.M. Rasmussen, K.R. Petrini, and R.T. Korbel. 2002. Squamous cell carcinoma in a greater Indian hornbill. Tierärztl. Prax. 2002: 214–218.