HEAD AND NECK
Radiology of the nasal cavity and paranasal sinuses Plain films (Fig. 1. 8) The frontal sinuses are not visible on the skull radiograph until the age of 2 years and achieve adult proportions by the age of 14. Asymmetry is common, and one or both may fail to develop. Absence of both may be associated with persistence of the metopic suture between the two halves of the frontal bone. Development of the ethmoids occurs at a rate similar to that of the frontal sinuses. Pneumatization of the sphenoid sinus commences at 3 years of age and may extend into the greater wings of sphenoid or clinoid processes. The degree of pneumatization is variable and relevant to transsphenoidal hypo¬ physectomy. The maxillary sinuses are the first to appear and are visible radiologically from a few weeks after birth. They continue to grow and develop throughout childhood. The tooth-bearing alveolar process does not begin to develop until the age of 6 years. Full pneumatization of the maxillary sinus is not achieved until there has been complete eruption of the permanent dentition in early adulthood. Computed tomography and MRI CT scanning in either axial or coronal planes provides excellent visualization of the paranasal sinuses (see Fig. 1. 12). Particular attention is paid to the region of the ostiomeatal complex, where the maxillary, frontal and anterior ethmoidal sinuses drain, and the sphenoethmoid recess and superior meatus, on to which the sphenoid and posterior ethmoid sinuses drain. The pneumatized sinuses should contain nothing but air. MRI is surprisingly good at demonstrating the sinuses, as the bony septa, which have no signal themselves, are lined by high-signal mucosa. The bone is seen as a lowintensity structure sandwiched between high-intensity mucosal layers. Air is also of low signal intensity. Embolization for epistaxis When cautery of the bleeding area and nasal packing and other surgical methods fail to control epistaxis, embolization may be successful. Angiographic assessment of the facial, sphenopalatine and greater palatine branches of the external carotid circulation is most likely to identify the source of bleeding. The ethmoidal branches of the ophthalmic artery may also need to be visualized and embolized. In all vessels, the microcatheter to be used for embolization must be advanced distal to branches with a high potential for dangerous anastomotic collaterals, such as the middle meningeal or ophthalmic arteries. Embolization of the superior labial branch of the facial artery is associated with necrosis of the nasal alae.
THE MANDIBLE AND TEETH The mandible (Figs 1. 13 and 1. 18) The mandible is composed of two halves united at the symphysis menti. Each half comprises a horizontal body and a vertical ramus joined at the angle of the mandible. The ramus has two superior projections, the coronoid process anteriorly and the condylar process posteriorly, separated by the mandibular (or condylar) notch. The coronoid process gives attachment to the temporalis muscle, and the condylar process (or head of mandible) articulates with the base of the skull at the temporomandibular joint. The body of the mandible bears the alveolar border with its 16 tooth sockets. The mandibular canal runs in the ramus and body of the bone, transmitting the inferior alveolar artery (branch of the maxillary artery) and nerve (branch of the mandibular division of the trigeminal nerve). The mandibular canal opens proximally as the mandibular foramen on the inner surface of the upper ramus, and its distal opening is the mental foramen on the external surface of the body below and between the two premolars. The muscles of the floor of the mouth, including the medial pterygoid muscles, are attached to the inner surface of the mandible and the muscles of mastication are attached to its outer surface.
The temporomandibular joint (Figs 1. 14-1. 16) This is a synovial joint between the condyle of the mandible and the temporal bone. The temporal articular surface consists of a fossa posteriorly, the temporomandibular fossa, and a prominence anteriorly, the articular tubercle. The head of the mandible sits in the fossa at rest and glides anteriorly on to the articular tubercle when fully open. The joint is least stable during occlusion.
13
