R. Davis, M.D., Juan M. Taveras, M.D., Glenn H. Roberson, M.D., Robert H. Ackerman, M.D., and James N. Dreisbach, M.D.

Transcription

1 Computed Tomography in Head Trauma Kenneth R. Davis, M.D., Juan M. Taveras, M.D., Glenn H. Roberson, M.D., Robert H. Ackerman, M.D., and James N. Dreisbach, M.D. OMFUTERIZED TOMOGRAPHY (CT) dem- C onstrates many of the effects of intracranial trauma better than any other imaging method. In many cases, it has obviated the need for other radiographic studies; in others, it has added complementary information that facilitates patient management. The advent of rapid CT scanners will lessen the need for sedation to prevent motion and extend the usefulness of the method. Epidural EXTRACEREBRAL Hematoma COLLECTIONS A recent epidural hematoma produces a biconvex extra-axial abnormality that falls within the absorption range of blood (20-45 EM1 units) (Fig. 1). Secondary mass effect may produce displacement of the midline and adjacent structures. The intimate attachment of the dura to the inner table does not permit diffuse spread of the blood as in subdural hematoma. The adherence is greatest in infancy and old age, so that epidural hematoma is not ordinarily encountered at the extremes of life.6 A positive CT scan with or without the demonstration of a fracture on the skull film is usually all that is radiographically necessary for the diagnosis. Epidural hematoma is a surgical emergency. Angiography may help demonstrate a bleeding point from the meningeal artery, but the patient may deteriorate neurologically during the additional time needed for this procedure. Subdural Hematoma An acute subdural hematoma shows a convex configuration along the inner table with a concave inner margin. As noted above, it is more diffuse than the epidural hematoma. The blood may settle to the dependent portion of the subdural compartment (Fig. 2). Midline displacement will be present if the collection is large enough. Underlying cerebral edema may also contribute to the mass effect. Occasionally, the hematoma may involve the interhemispheric (Fig. 3) or infratentorial subdural space. A contralateral subdural hematoma may first become evident or enlarge after a subdural hematoma is evacuated (Fig. 4). Rarely, a subdural hematoma may result from a ruptured aneurysm or a fall sustained by a patient suffering from another ailment, such as hypertensive intracerebral hematoma. A false-negative CT scan may sometimes be encountered in- the presence of bilateral subdural hematomas usually in the subacute or chronic stage.5 There is no midline shift in these patients since the subdural collections and associated cerebral edema Kenneth R. Davis, M.D.: Assistant Radiologist, Massachusetts General Hospital, and Assistant Professor, Harvard Medical School, Boston, Mass. Juan M. Taveras, M.D.: Radiologist-in-Chief, Massachusetts General Hospital, and Professor, Harvard Medical School, Boston, Mass. Glenn H. Roberson, M.D.: Associate Radiologist and Head Neuroradiology Section, Massachusetts General Hospital, and Assistant Professor, Harvard Medical School, Boston, Mass Robert Ackerman, M.D.: Assistant Radiologist, Massachusetts General Hospital, and Assistant Professor, Harvard Medical School, Boston, Mass. James Dreisbach, M.D.: Fourth Year Resident in Radiology, Massachusetts General Hospital, and Clinical Fellow, Harvard Medical School, Boston, Mass. Reprint requests should be addressed to Kenneth R. Davis, M.D., Department of Radiology, Massachusetts General Hospital, Boston, Mass by Grune & Stratton, Inc. Fig. 1. Epidurrl hrmatoma. Biconvex araa of recent blood absorption values (black arrow) with minimal ccimpression of the ipsilateral ventricle and shift of septum pellucidurn (white arrow). Seminars in Roenfgenotogy, Vol. XII, No. 1 (January),

2 DAVIS ET AL. Fig. 3. Interhemispheric subdural hematoma (arrow). Fig. 2. Subdural hematoma. The diffuse extra cerebral collection parallels the cortical convexity. Sedimentation of the blood (arrows) accounts for the layering. Shift of midline structures is striking (arrowhead). Fig. 4. Development of contralateral subdural hematoma. Top row: Left subdural hematoma (arrows). Bott :om / row: One day after evacuation of the hematoma. A large right subdural hematoma is now apparent (arrows). A left occ :ipital contusion or swelling is present (arrowhead). The right posterior temporal bone defect was the result of surgery al tan early age.

3 COMPUTED TOMOGRAPHY IN HEAD TRAUMA 55 iron play no significant role in the high absorption of a hematoma A large isodense unilateral subdural collection, although it shifts the midline, will be more readily depicted by angiography than by a CT scan. The use of high dose intravenous contrast medium infusion may enhance the surrounding brain a few EMI units, making the subdural collection more or less apparent. The contrast medium may actually collect in the subdural hematoma, thereby making an inconspicuous collection more apparent. The fluid in a chronic subdural hematoma has a low absorption range (Fig. 5).13 The contents of a Fig. 5. Right chronic subdural hematoma. Low absorption fluid collection (arrows). Compressed right lateral ventricle, and enlarged left lateral ventricle. are equal on the two sides, but the ventricles will be small due to compression. Furthermore, the subdural collection may become similar in density to adjacent brain (isodense), usually days after onset5 as well as in patients with marked anemia. The high absorption abnormality of the blood, dependent on the protein concentration in the hemoglobin, decreases with time. Calcium and Fig. 6. Subdural empyema. Biconvex low absorption abnormality (arrows) with contrast enhancement of its inner margin. Fig. 7. &frontal atrophy versus chronic subdural hematoma. (A) Inward extension of the digitations of the enlarged sulci (arrow), enlargement of the interhemispheric fissure (arrowhead), and lack of a mass effect on the enlarged frontal horns indicate atrophy. (B) Another patient. Smoothly marginated subdural spaceand ventricular compression indicate chronic subdural hematomas.

4 56 DAVIS ET AL. subdural empyema may show similar low absorption, but the shape is more often biconvex than the average chronic subdural hematoma, and the dura often has elevated absorption values after contrast medium enhancement (Fig. 6). A false-positive CT scan for recurrent subdural hematoma may occur when there has not yet been re-expansion of the brain following evacuation of a large, long-standing chronic subdural hematoma. A recent re-bleed should show higher absorption values (20-45 EM1 units) compared to the usual postoperative residual collection. A large extracerebral space resulting from cortical atrophy may also simulate chronic subdural hematoma (Fig. 7). The adjacent sulci are often enlarged in atrophy. When the question of chronic subdural hematoma on CT scan cannot be resolved and the diagnosis is suggested clinically, a technetium pertechnetate scan or, ultimately, angiography may be indicated. the findings are analogous to those in subdural hematomas. INTRACEREBRAL HEMORRHAGE Superficial or deep intracerebral hemorrhage may occur following trauma (Fig. 9). A small cryptic arteriovenous malformation may be the cause Hygroma (Arachnoid Cyst) A hygroma (usually associated with a hypoplastic temporal lobe) may have a typical appearance on CT scan, as seen in Fig. 8. Elevation of the sphenoid wing on the plain skull films will often be present. This form is probably associated with trauma in infancy; if the injury occurs later, Fig. 8. Hygroma with hypoplastic temporal lobe. Note the low absorption abnormality with sharply angulated borders located in the anterior portion of the right middle fossa. Fig. 9. Hematoma in the rostrum of the corpus callosum. No abnormality was suspected prior to CT scan, since the patient had no significant neurologic findings. Resolution of the hematoma (arrows) over a period of 3 weeks. (A) November 30; (B) December 1; (C) December 8: ID) December 32.

5 COMPUTED TOMOGRAPHY IN HEAD TRAUMA 57 Fig. 10. Multiple hematomas with progressive enlargement. (A and B) Hematoma in the splenium of the corpus callosum (arrow) and small hematoma in the right putamen (arrowhead). (C and D) Two days later. Increase in size of the putamen hemorrhage (arrows). in some cases, but is not ordinarily detected by angiography. Spasm of nearby vessels is commonly seen at angiography when the trauma is severe and blood enters the subarachnoid space. The hematoma may later enlarge, accompanied by further neurologic deterioration (Fig. 10). Without a CT scan, an intracerebral hemorrhage may be readily overlooked even though a subdural hematoma is recognized and evacuated at surgery (Fig. 11). Hemorrhage into a tumor, such as a glioblastoma or metastatic malignant melanoma, may occasionally occur. An adjacent area of irregular contrast enhancement due to the neoplasm helps in the differential diagnosis. A relatively smooth and thin rim of contrast enhancement may, however, occasionally be seen surrounding a simple hematoma. Low absorption abnormality due to edema or contusion around a traumatic hematoma may be difficult to differentiate on a plain CT scan from edema around a bleeding tumor,2y13 but the enhancement scan may be helpful. A recent hypertensive thalamic or putaminal hemorrhage shows little surrounding low absorption change,s7r4 Fig. 11. Intraarebral hsmatoma missed at emergency surgical evacuation of a left subdural hematoma and bifrontal decompression. Lack of clinical improvement led to a CT scan. Frontal hematoma (arrow) and intraventricular hemorrhage (double arrows) were demonstrated.

6 Fig. 12. lntraventricular hemorrhage. The patient had minimal neurologic deficit after a motor vehicle accident. Top row: Blood in the ventricles (arrows). Bottom row: Four days later. Marked decrease in intraventricular blood. Fig. 13. Heterogeneous confluent petechial hemorrhages in a patient with bilateral frontal lobe contusions (arr Right anterior temporal hematoma (arrowhead), right subdural hematoma (double arrows), intraventricular blood, 18 shift are also shown on these cuts. 58 owl. and

7 Fig. 14. Serial scans following head trauma. The ventricles become slit-like (arrow) 7 days after injury because of bilateral cerebral edema. Progressive enlargement of the lateral ventrides over the next 4 months is due to communicating hydrocephalus and resolution of the edema. whereas hemorrhage into an area of infarction is surrounded by a much wider and irregular area of low absorption infarcted tissue? Intracerebral hemorrhage secondary to aneurysm may be indistinguishable from traumatic hemorrhage without a clinical history and possible angiography.3 In traven tricular Hemorrhage When small, intraventricular hemorrhage is commonly associated with minimal neurologic deficit (Fig. 12). A large hemorrhage is associated with neurologic signs of hydrocephalus, as well as findings related to specific areas of brain damage. Contusion and Swelling A contusion may contain only small scattered petechial hemorrhages not visible on current CT scans, unless they are confluent (Fig. 13). A low absorption area of edema may be the only CT finding when these scattered petechial hemorrhages are present (Fig. 4). Cerebral swelling or edema may be reflected only as ventricular compression without definite evidence of low absorption abnormality (Fig. 14). Ventricular compression may become evident if an early scan prior to swelling is also available. Otherwise, serial scans may be necessary in order to appreciate the re-expansion of the ventricles. How- Fig. 15. Normal CT scan passing through upper brainstem after lumbar injection of Metrizamide. The shape of the cerebral peduncles and the interpeduncular fossa are clearly shown (arrows). Fig. 16. Skull fracture with large depressed fragment (arrows).

8 60 DAVIS ET AL. ever, posttraumatic hydrocephalus may also develop (Fig. 14). Brainstem swelling due to injury is difficult to visualize on current CT scans. Intrathecal injection of Metrizamide, a water-soluble contrast agent, holds promise since it improves visualization of the outline ofthe brainstem (Fig. 15). DEPRESSED SKULL FRACTURE Evaluation of the amount of depression of fracture fragments may be assessed by CT scan (Fig. 16). Localization of a superficial fragment as well as a deep intracerebral fragment may be achieved. FOREIGN OBJECTS Penetrating bullet wounds may produce hemorrhage, contusion, and swelling. CT will demonstrate these features as well as localize the bullet fragments (Fig. 17). A ventricular puncture may produce a hematoma along the needle track. This is easily identified on CT scan (Fig. 18). Intraorbital localization of a foreign object by CT is illustrated in Fig. 19. CT is more sensitive to many objects that are poorly seen on radiographs, while also displaying the adjacent structures. A secondary abscess may be identified. PNEUMOCEPHALUS Open head injury may result in pneumocephalus (Fig. 20). Traumatic perforation of the ethmoidal, frontal, or sphenoidal sinuses and the adjacent dura may produce pneumocephalus. SEQUELAE OF TRAUMA AND DELAYED COMPLICATIONS Communicating hydrocephalus (Fig. 14) may require a shunt. The ventricles are readily depicted Fig. 17. Bullet wound. lop row: Day of injury. (A) Star artifaot produced by bullet fragments (black arrow). (B) Hemorrhage and contusion along the bullet path (arrowheads). (C) Exit wound (two black arrows). Bottom row: Six weeks later. (D) Shift of septum pellucidurn and third ventricle (arrowhead) to side of evacuated hematoma, probably secondary to posttraumatic atrophy. (El Contrast enhancement in capsule of subsequently proven abscess (arrows).

9 COMPUTED TOMOGRAPHY IN HEAD TRAUMA 61 Fig. 18. Homatoma along ventricular needle track in right frontal lobe. (A) Hematoma (arrow). (B) Measuring mode has been set at M40 to demonstrate the hematome (arrow). (Cl Setting at MlOO, above blood density level to demonstrate the ventricular needle (arrows). and the hydrocephalus is apparent on the CT scan. Metrizamide may permit evaluation of cerebrospinal flow patterns when it becomes generally available. A small pneumocephalus is seen better on CT scans than on skull films (Fig. 20). Pneumocephalus may occur late due to communication with a sinus or to infection.6 Further bleeding may take place after the initial trauma (Fig. IO), particularly when the blood pressure rises out of control. After evacuation of a large subdural hematoma on one side, a subdural hematoma may become evident on the opposite side (Fig. 4), possibly by releasing a tamponade effect. Atrophy may result following trauma (Fig. 17). Ipsilateral ventricular shift and enlargement and cortical atrophy may be seen. Following evacuation of a chronic subdural hematoma, the brain may be slow to re-expand. An abscess may occur after a penetrating or open injury (Fig. 17). Plain and contrast enhancement CT scans will generally depict a high absorption capsule after a sufficient time interval. A leptomeningeal cyst may follow a fracture. CT will show the intracranial extent of the cyst and Fig. 19. Piece of glass in left orbit (blade arrow). Globe (white arrows). The foreign body was not clearly seen on ordinary radiographs of the orbit, including polytome laminography.

10 62 DAVIS ET AL. Fig. 20. Pneumocephalus following a severe injury. (A) Left frontal extracerebral air is present. (B) Air over cerebral convexities (arrows) surrounded by computer artifact (white halo) due to very low absorption values of air. Depressed skull fracture is seen posteriorly (arrowheads). the bone defect, whereas skull films will demonstrate the typical bone changes in more detail. REFERENCES 1. Ambrose.I: Computerized x-ray scanning of the brain. J Neurosurg 40: , Baker HL, Campbell JK, Houser OW, et al: Computer assisted tomography of the head: An early evaluation. Mayo Clin Proc 49:17-27, Davis KR, New PFJ, Ojemann RG, et al: Computerized tomographic evaluation of hemorrhage secondary to intracranial aneurysm. Am J Roentgen01 (in press) 4. Davis KR, Taveras JM, New PFJ, et al: Cerebral infarction diagnosis by computerized tomography. Am J Roentgen01 124: , Davis KR, Taveras JM, Roberson GH, et al: Some limitations of computerized tomography in diagnosis of neurological diseases. Am J Roentgen01 (in press) 6. Greenfleld JG, Russel DS: Traumatic lesions of the central and peripheral nervous systems, in Greenfield M (ed): Neuropathology. Baltimore, Williams & Wilkins, 1963, pp Greitz T, Hindmarsh T: Computer assisted tomography of intracranial CSF circulation using water-soluble contrast medium. Acta Radio1 [Diagn] 15: , Hier DB, Davis KR, Richardson EP, et al: Hypertensive putaminal hemorrhage. Arch Neurol (in press) 9. Merino-de Villasante J, Taveras JM: Computerized tomography (CT) in acute head trauma. Am J Roentgen , Messina AV: Computed tomography: Contrast media within subdural hematomas. A preliminary report. Radiology 119~ , Messina AV, Chernick NL: Computed tomography: The resolving intracerebral hemorrhage. Radiology 118: , New PFJ, Aronow S: Attenuation coefficients of whole blood fractions in computed tomography. Radiology (in press) 13. New PFJ, Scott WR, Schnur JA, et al: Computerized axial tomography with the EM1 Scanner. Radiology 110: , Scott WR, New PFJ, Davis KR, et al: Computerized axial tomography of intracerebral and intraventricular hemorrhage. Radiology 112: 73-80, 1974