Head and Soft Tissues of Face and Neck

Normal Skull and Variants

Normal anatomy of the skull is shown in Fig. 2.1 . The most common differential problem on plain skull x-rays is distinguishing cranial sutures from vascular grooves and fractures. The main sutures are coronal, sagittal, and lambdoid. A suture also runs in a rainbow shape over the ear. In the adult, sutures are symmetric and very wiggly and have sclerotic (very white) edges. Vascular grooves are usually seen on the lateral view and extend posteriorly and superiorly from just in front of the ear. They do not have sclerotic edges and are not perfectly straight.

A few common variants are seen on skull x-rays. Hyperostosis frontalis interna is a benign condition of females in which sclerosis, or increased density, is seen in the frontal region and spares the midline ( Fig. 2.2 ). Large, asymmetric, or amorphous focal intracranial calcifications should always raise the suspicion of a benign or malignant neoplasm. Occasionally, areas of lucency (dark areas) are found where the bone is thinned. The most common normal variants that cause this are vascular lakes or biparietal foramen. Asymmetrically round or ill-defined holes should raise the suspicion of metastatic disease ( Fig. 2.3 ).

Paget disease can affect the bone of the skull. In the early stages, very large lytic, or destroyed, areas may be seen. In later stages, increased density (sclerosis) and marked overgrowth of the bone, causing a cotton wool appearance of the skull, may be seen ( Fig. 2.4 ). Always be aware that both prostate and breast cancer can cause multiple dense metastases in the skull and that both diseases are more common than Paget disease.

Normal Anatomy

Box 2.1 gives a methodology to follow or checklist of items to use when examining a computed tomography (CT) scan. Both CT and magnetic resonance imaging (MRI) are capable of displaying anatomic slices in a number of different planes. The identical anatomy of the brain can appear quite different on CT and magnetic resonance (MR) images ( Fig. 2.5 ). The normal anatomy of the brain on CT and MR images is shown in Figs. 2.6 and 2.7 . You should be able to identify some anatomy on these images. There are many very complex imaging sequences used during MRI, depending upon the clinical question or suspected pathology. You are not expected to be familiar with all of these, but you should realize that success in making a diagnosis depends on your indicating the clinical problem accurately so that the radiologist can prescribe the correct imaging sequences.

Intracranial Calcifications

Intracranial calcifications can be seen occasionally on a skull x-ray, but they are seen much more often on CT. Intracranial calcifications may be due to many causes. Normal pineal and ependymal calcifications may occur. Scattered calcifications can occur from toxoplasmosis, cysticercosis, tuberous sclerosis ( Fig. 2.8 ), or granulomatous disease. Unilateral calcifications are very worrisome because they can occur in arteriovenous malformations, gliomas, and meningiomas.

Headache

Headaches are among the most common of human ailments. They can be due to a myriad of causes and should be characterized by location, duration, type of pain, provoking factors, and age and sex of the patient. In the primary care population, less than 0.5% of acute headaches are the result of serious intracranial pathology. Simple headaches, tension headaches, migraine headaches, and cluster headaches do not warrant imaging studies. A good physical examination is essential, including evaluation of blood pressure, urine, eyes (for papilledema), temporal arteries, sinuses, ears, neurologic system, and neck. In a patient with a febrile illness, headache, and stiff neck, a lumbar puncture should be performed. In only a few circumstances is imaging indicated ( Box 2.2 ).

In general, imaging is indicated when a headache is accompanied by neurologic findings, syncope, confusion, seizure, and mental status changes or after major trauma. Sudden onset of the “worst headache of one's life” (thunderclap headache) should raise the question of subarachnoid hemorrhage. Sudden onset of a unilateral headache with a suspected carotid or vertebral dissection or ipsilateral Horner syndrome should prompt a CT or MR angiogram.

Sinus headaches can usually be differentiated from other causes because they worsen when the patient is leaning forward or when pressure is applied over the affected sinus. Indications for CT use in sinus headaches are presented in Box 2.3 .

Hearing Loss

Hearing loss is characterized as conductive, sensorineural, or mixed. Conductive loss results from pathology of the external or middle ear that prevents sound from reaching the inner ear. Sensorineural loss results from abnormalities of the inner ear, including the cochlea or auditory nerve. CT is the best technique for evaluating conductive loss and the bony structures of the middle ear. Not all patients with conductive loss need a CT scan. Indications include complications of otomastoiditis, preoperative and postoperative evaluation of prosthetic devices, cholesteatoma, and posttraumatic hearing loss. Sensorineural hearing loss may be sudden, fluctuating, or progressive and may also be associated with vertigo. It can be due to viral infection, eardrum rupture, acoustic neuroma, or vascular occlusive disease. Evaluation is best done by MRI, with and without intravenous contrast.

Head Trauma

On skull x-rays, fractures are dark lines that have very sharp edges and tend to be very straight ( Fig. 2.9 ). If a fracture is present over the middle meningeal area, an associated epidural hematoma may be found. If a depressed fracture is present, the lucent fracture lines can be stellate or semicircular ( Fig. 2.10 ). In either of these cases, substantial brain injury may be present and a CT scan, including bone windows, is indicated.

Skull x-rays are ordered much too frequently. A skull fracture without loss of consciousness is very rare. Significant brain injury may be found without a skull fracture. The patient should be examined clinically and a decision made as to whether the physical findings and history indicate a moderate to severe head injury or mild head injury. CT, MRI, or skull radiography is not needed for low-risk patients. Low-risk patients are defined as those who are asymptomatic or have only dizziness, mild headache, scalp laceration, or hematomas, are older than 2 years, and have no moderate- or high-risk findings.

Patients at moderate risk are those who have any of the following conditions: history of change in the level of consciousness at any time after the injury, progressive or severe headache, posttraumatic seizure, persistent vomiting, multiple trauma, serious facial injury, signs of basilar skull fracture (e.g., hemotympanum, “raccoon eyes,” cerebrospinal fluid [CSF] rhinorrhea or otorrhea), suspected child abuse, bleeding disorder, or age younger than 2 years (unless the injury is trivial).

High-risk patients are those with any of the following conditions: focal neurologic findings, a Glasgow Coma Scale score of 8 or less, definite skull penetration, metabolic derangement, postictal state, or decreased or depressed level of consciousness (unrelated to drugs, alcohol, or other central nervous system [CNS] depressants). If a moderate or severe injury is present and the patient is neurologically unstable, a CT scan should be done to exclude a hematoma. If the patient is neurologically stable, an MR scan is preferable to look for parenchymal shearing injuries. In mild head injury (with no loss of consciousness or neurologic deficit), the patient may be observed. There are three sets of prediction rules as to who does not need CT imaging: New Orleans Criteria (NOC), Canadian CT Head Rule (CCHR), and National Emergency X-Radiography Utilization Study (NEXUS II). If a patient has any of the following, a CT scan may be indicated; headache, vomiting, age older than 60 years, alcohol or drug intoxication, deficit in short-term memory, seizure, visible trauma above the clavicles, fall from more than three feet or five steps, coagulopathy, scalp hematoma, acute focal neurologic deficit, or skull fracture. If a persistent headache occurs after trauma, CT scanning should be performed.

Suspected Intracranial Hemorrhage

If the presence of acute intracranial hemorrhage is suspected, the study of choice is a CT scan without intravenous contrast. The scan is done without contrast because acute hemorrhage appears to be white on a CT scan ( Fig. 2.11 ) and so does intravenously administered contrast. Hemorrhage into the ventricles is usually seen in the posterior horns of the lateral ventricles. Blood is denser than CSF and therefore settles dependently. This settling process is not seen with subarachnoid or intraparenchymal blood. The presence of hemorrhage is a contraindication to anticoagulation.

Intraparenchymal bleeding can result from a ruptured aneurysm, stroke, trauma, or tumor. Grave prognostic factors are large size and brainstem location. Most hypertensive bleeds (80%) occur in the basal ganglia, 10% occur in the pons, and 10% in the cerebellum. An associated mass effect may be present with compression of the ventricles or midline shift. The findings of acute hemorrhage on a noncontrast CT scan indicate increased density in the parenchyma ( Fig. 2.12 ). Differentiation from calcification usually is easily made by clinical history and, if necessary, by having the area of interest measured on the scan in terms of density (Hounsfield units).

Subdural hematomas are seen as crescent-shaped abnormalities between the brain and the skull. They can cross suture lines, but they do not cross the tentorium or falx. In some cases, subdural hematomas can be quite difficult to see because new blood appears denser or whiter than brain tissue ( Fig. 2.13A ). As the blood ages (over a period of several weeks), it becomes less dense than the brain (see Fig. 2.13B ). Obviously, it follows that a subacute phase occurs during which the blood is the same density as the brain (isodense). In this stage, sometimes the only clue that a subdural hematoma is present is effacement of the gyral pattern on the affected side, a midline shift away from the affected side, or ventricular compression on the affected side.

Epidural hematomas follow the same changing pattern of density as do subdural hematomas. The major differential point from an imaging viewpoint is that they are lenticular rather than crescentic ( Fig. 2.14 ) and tend not to cross suture lines of the skull. Epidural hematomas are associated with temporal bone fractures that have resulted in a tear of the middle meningeal artery.

Subarachnoid hemorrhage is usually the result of trauma or a ruptured aneurysm. It is most often accompanied by a very severe sudden-onset headache. Subarachnoid hemorrhage can really be visualized only in the acute stage, when the blood is radiographically denser (whiter) than the CSF. The most common appearance is increased density in the region around the brainstem in a pattern sometimes referred to as a Texaco star ( Fig. 2.15 ). Increased density due to the presence of blood also can be seen as a white line in the sylvian fissures, in the anterior interhemispheric fissure, or in the region of the tentorium. In the absence of trauma, a ruptured aneurysm should be suspected. As discussed in Chapter 9 , in infants, both intraventricular and intraparenchymal hemorrhage can be visualized and monitored by using ultrasound. This can be done only if the fontanelles have not closed.

Pneumocephalus

Air within the cranial vault is almost always the result of trauma. Even tiny amounts of air are easily seen on CT as decreased density (blackness; see Fig. 2.11 ). It is preferable to do a CT scan instead of an MRI examination because of the superior ability of CT to localize skull fractures and fresh hemorrhage. It also is easier to manage an unstable patient in a CT scanner than in an MRI machine.

Hydrocephalus

Dilatation of the ventricles can be obstructive or nonobstructive. The ventricles are easily seen on a noncontrast CT or MRI study. If the cause is obstructive, both modalities have a good chance of finding the site of obstruction.