Radiological Demonstration of the Zygomatic Arch

One of the usually more difficult radiological technical problems is adequate demonstration of the zygomatic arch. This prominent facial structure is important to the plastic surgeon because of traumatic external deformities; to the ophthalmologist because trauma changes the orbital shape and eye levels, with resulting diplopia of serious nature; to the rhinologist because of injuries to the maxillary antrum; to the dentist because depression can interfere with the mandibular articulations and movement of the coronoid process and muscles of the jaw, producing bite deformities. The projections used by most technicians fail to produce views at these levels sufficiently measurable and comparable to give the radiologist and clinician a clear idea of the scope of the problem. The zygomatic arch is composed of several bony parts. The main structure is the malar bone, which is a roughly rectangular plate. This is attached anteriorly to a projection from the maxillary bone, superiorly to a projection from the combined frontal and sphenoid bones, and posteriorly to a projection from the temporal bone. The relatively free malar borders between the bone attachments of the maxillary process and the frontosphenoid process form the lateral border and a portion of the inferior border of the orbit. Unfortunately, injury of the zygomatic arch usually involves several of the bony parts and is quite often compounded into the maxillary sinus. The number of fractures and their location, the magnitude of the depressions in the arch, and the shifts of bone mass have to be shown by various technical positions, with the uninjured side serving as a model for the injured side. These views are preferably taken at right angles to each other to present the maximum deviations in the various planes. Three routine views, all of which show the opposite side for comparison, will demonstrate the arch in its entirety and will give measurable evidence of the amount of deformity involved. The first view is obtained in the usual nose-chin position for the maxillary sinus study. The nose and chin rest on the table top over the mid-line of the table and cassette, with the mid-line sagittal section of the head vertical to the table top. The tube is placed with the central ray perpendicular to the table top and projecting through the floor of the orbits to pick up the inferior orbital ridges. This view is taken with a Bucky, with the average factors, for an average patient thickness of 23 cm., of 74 kv.p., 50 ma. sec., 40 in. focal skin distance. The film thus obtained outlines the inferior orbital ridge and will outline fractures in this area of the maxilla, demonstrating measurably any downward depression of the inferior orbital ridge, in addition to showing maxillary antral changes. The arch itself is not demonstrated, and both sides are shown for comparison in a single view.