Hyperostosis frontalis interna (enostosis crani) ( Fig. It is of no clinical significance and is differentiated from pineal gland calcification by its smaller size and C-shaped configuration. Habenular calcification appears as a characteristic C-shaped or comma-shaped radiodensity sometimes noted on plain film and commonly noted on CT scans. Rarely, hypoplasia of the frontal sinuses presents with sinusitis, bronchiectasis, and situs inversus together this latter triad is known as Kartagener (dyskinetic cilia) syndrome. The frontal sinuses commonly lack symmetry (hypoplasia), or are completely missing on one or both sides (aplasia). Encephaloceles may be associated with Meckel-Gruber syndrome, microcephaly, cystic dysplastic kidneys, and polydactyly Magnetic resonance imaging details the type and extent of the lesion. Ultrasound is used for antenatal evaluation. Encephaloceles are most common in the occiput, and may be supratentorialor infratentorial. Computed tomography (CT) and magnetic resonance imaging additionally demonstrate a small or absent pituitary gland.Īn encephalocele is the extension of intracranial tissue through a cranial defect.

Usually beginning during the third decade it should be differentiated from the punctuate cortical and linear basal ganglia calcifications that are associated with toxoplasmosis.ĭermoids are small (16 mm, or depth >12 mm). It is noted as a stippled pattern of calcification located immediately superior to the orbits on a frontal projection and slightly superior and posterior to the pinna of the ear on the lateral film. 7-4 The lateral view of the skull exhibits a radiolucent band representing the dural venous sinus (arrows).Ĭalcification of the choroid plexus is one of the most common normal intracranial calcifications, nearly always occurring in the lateral ventricles. This may be associated with Chiari type 1 malformation, and magnetic resonance imaging often is indicated.įIG. This is diagnosed by observing the tip of the dens significantly above McGregor’s line (in this case >15 mm). 7-3 Complete bony assimilation of C1 to occiput (occipitalization) and congenital basilar impression. 7-2 Multiple hair pins obstructing the view of the lower skull.įIG. 7-1 A bullet and related trail of lead fragments is noted in this ambulatory patient who presented to a chiropractor’s office.įIG. A multiple layer (lamellar) appearance of calcification is seen in Gorlin syndrome.įIG. It is related to infection, trauma, and normal aging. Basilar impression increases the risk of neurologic damage and circulatory embarrassment.Ī calcified cerebral falx appears as a single sheet of calcification extending from the frontal bone. If the resulting angle (Martin’s basilar angle, see Chapter 4) is greater than 152 degrees, platybasia is present. Platybasia is assessed by constructing approximations of the hard palate and clivus. (See Chapter 4 for more detail on construction of these roentgenometrics.) In contrast to describing the relationship of the odontoid to the skull base, as is done for basilar invagination, the term platybasia (meaning “flat base”) describes the morphology of the skull base without using the odontoid as a reference point. The deformity is identified on the lateral projection by constructing lines from the posterior extreme of the hard palate to either the posterior margin of the foramen magnum (Chamberlain’s line) or lower margin of the base of the occiput (McGregor’s line), and examining the distance between the constructed line and the tip of the odontoid process. Primary basilar impression is also known as Bull-Nixon syndrome. The presentation is either primary (congenital syndromes such as Klippel-Feil syndrome and Arnold-Chiari malformation) or acquired (bone softening pathologies such as osteomalacia, fibrous dysplasia, or Paget’s disease). Although some authors separate the upward displacement of the foramen magnum (basilar invagination) from the resulting deformity of the skull base (basilar impression), most sources use the terms as synonyms. It is discussed more fully in Chapter 33.īasilar invagination describes a cephalic deformity of the margins of the foramen magnum with resulting deformity of the condyles and skull base (basilar impression). TABLE 7-1 Skeletal Variants, Anomalies, and Defects of the SkullĬommon artifacts visualized are hearing aids, hairpins, dental fillings, etc.Īrnold-Chiari malformation describes the presence of a myelomeningocele with varying degrees of caudal displacement of the cerebellar tonsils and hindbrain.

Cervical spine x ray down's syndrome