| OCR Text |
Show Journal of Clinical Neuro-ophthnlmology 13(1)' 50-53, 1993. Free Air in the Cavernous Sinus as an Incidental Finding Jonathan c. Horton, M.D. Ph.D., Paul D. Langer, M.D., and Gary E. Turner, M.D. © 1993 Raven Press, Ltd , l\lew York Free air within the cavernous sinus was discovered incidentally on a computed tomographic (CT) scan. We suggest that air bubbles were introduced inadvertently when contrast material was injected just prior to CT scanning, On a repeat CT scan 16 days later, the air had disappeared. Key Words: Cavernous sinus-Air bubble-Computed tomography. From the Departments of Ophthalmology, Radiology, and Neurosurgery, University of California, San Francisco, San Francisco, California, U.s.A. Address correspondence and reprint requests to Dr. Jonathan c. Horton, Department of Ophthalmology, University of California, San Francisco, San Francisco, CA 94143-0730, U.S.A. 50 Free air in the cavernous sinus has been shown with computed tomography in patients with septic thrombosis (1), skull fracture (2), and barotrauma (3). It has also been described in the dural sinuses after penetrating craniocerebral trauma (4). Free air in the cavernous sinus has not been reported as a benign, incidental finding in a healthy patient. CASE REPORT A 50-year-old man sought evaluation in the ophthalmology clinic for long-standing, painless visual loss in the right eye. The visual acuity could be corrected to only 20/60. The right optic disc appeared pale and atrophic. A contrast-enhanced computed tomography (CT) scan was ordered to investigate the possibility of compression of the optic nerve by a tumor, The patient was placed upon a gurney with the head of the stretcher elevated at 45°. An intravenous line was started in the right volar forearm and a bolus of 100 cc of iohexol contrast material (Omnipaque 300) was injected. Contiguous 1.5mm axial CT images were subsequently obtained through the orbits and the perisellar region. The scan showed no abnormality of the globes or the optic nerves. The cause of visual loss in the right eye was never firmly established, but an old ischemic optic neuropathy was presumed to be responsible. The remarkable finding on the CT scan was free air within the cavernous sinus. There were two circular bubbles located along the lateral wall of the right cavernous sinus (Fig. 1). The posterior bubble was slightly larger and nearer to the posterior apex of the sinus. It measured minus 373 Hounsfield units. On an axial section just below the bubbles, small irregular lucencies compatible with fat were FREE AIR IN CAVERNOUS SINUS 51 (A) (C) present within both cavernous sinuses (Fig. lA, arrows). On axial bone windows, the bubbles within the right cavernous sinus appeared isodense with air in the ethmoid and sphenoid sinuses (Fig. 2). No fractures of the bones of the orbits, sinuses, or cranium were seen. To confirm our impression that the bubbles represented free air within the right cavernous sinus, the patient was rescanned 16 days later. On this occasion, no contrast agent was administered and no intravenous line was inserted. Matching contiguous axial CT sections were obtained (Fig. 3). The two bubbles within the right cavernous sinus were absent. The low-density structures consistent with fat, noted previously in each cavernous sinus, were unchanged in appearance (Fig. 3A, arrows). (B) FIG. 1. (A-C) Contrast-enhanced axial CT images showing two small air bubbles in the right cavernous sinus with a reading of - 373 Hounsfield units. These serial cuts are 1.5 mm thick. On image (A), small fat densities measuring - 54 Hounsfield units are visible in both cavernous sinuses (arrows). DISCUSSION On a CT scan obtained in search of an optic nerve tumor, we found two small, round, lowdensity areas within the right cavernous sinus. We interpreted these low-density areas as free air, based upon their appearance and their Hounsfield reading of minus 373 units. Small quantities of intracranial or intravascular air are rapidly resorbed by the body. The disappearance of the bubbles on the follow-up scan supports their identification as free air. Lobules of fat are occasionally present within the cavernous sinus, and have been confused with free air (5). In our patient, small collections of fat were identified in each cavernous sinus (Fig. lA, arrows). They were distinguished from air on the J Clin Neuro-ophthalmol, Vol. 13, No.1, 1993 52 (A) (C) J. C. HORTON ET AL. (8) FIG. 2. (A-C) Bone windows of scan illustrated in Fig. 1, Note that the bubbles in the right cavernous sinus have the same density as air in the paranasal sinuses. basis of their greater density, irregular contour, and unchanged appearance on repeat scanning (Fig. 3A, arrows). Free air in the cavernous sinus signifies a potential neurological or neurosurgical emergency. It has been reported as a sign of cavernous sinus thrombosis due to gas-forming organisms (1). Our patient was entirely healthy, so infection cannot be invoked as an explanation for the air in his cavernous sinus. Moreover, we were unable to elicit a history of recent sinusitis, trauma, flying, diving, or drug snorting or injection. It seems unlikely that air could pass directly from the contiguous paranasal sinuses through bone and dura into the cavernous sinus. It is equally improbable that air from an arterial source could reach the cavernous sinus after passing through the cerebral circulation. J elin Neuro-ophthalmol, Vol. 13, No.1. 1993 We postulate that air bubbles, introduced along with contrast administration before the CT scan, may have traveled retrogradely up the internal jugular vein, petrosal sinuses, and into the cavernous sinus. Frequently, tubing is not purged adequately of small air bubbles before starting intravenous lines. Venous air bubbles normally pass via the right heart to the pulmonary capillaries, where they are trapped and absorbed. In this patient, we suspect that at the moment the air reached the right brachiocephalic vein, a well-timed cough or Valsalva maneuver propelled the bubbles into the internal jugular vein where they rose against the flow of blood. Orrell and coworkers (6) reported a patient with septic cavernous sinus thrombosis and an air bubble visualized on a contrast CT scan. Hemophilus FREE AIR IN CAVERNOUS SINUS 53 (A) (C) influenza meningitis was diagnosed after examination of the cerebrospinal fluid. This organism does not form gas, leading the authors to speculate that the air entered the cavernous sinus from noseblowing. In another recent case, Canavan and Osborn (3) found numerous air bubbles in the cavernous, straight, left transverse, and superior sagittal sinuses of a man who presented to an emergency room with right temporal headache from a decayed tooth. The patient had been flying earlier the same day in a hobby plane. Although he never exceeded an altitude of 6,000 ft, the authors attributed his intracranial air to barotrauma. We offer a new explanation for the air within the cerebral dural sinus in these cases: iatrogenic introduction by intravenous injection prior to CT scanning. Our case serves as a caution that free air within the cerebral dural sinuses does not always (8) FIG. 3. (A-C) Repeat scan, performed 16 days later without contrast, showing disappearance of air bubbles in the right cavernous sinus. The fat densities (A) are still present (arrows). represent a neuroradiological sign with grave implications. It may be nothing more than an artifact of CT scanning with intravenous injection of contrast material and air. REFERENCES 1. Cumes JT, Creasy JL, Whaley RL, Scatliff JH: Air in the cavernous sinus: a new sign of septic cavernous sinus thrombosis. AJNR 1987;8:176-7. 2. Bartynski WS, Wang AM: Cavernous sinus air in a patient with basilar skull fracture: CT identification. J Comput Assist Tomogr 1988;12:141-2. 3. Canavan L, Osborn RE: Dural sinus air without head trauma or surgery: CT demonstration. JComput Assist Tomogr 1991;15:526-7. 4. Crone KR, Lee KS, Moody DL, Kelly DL Jr: Superior sagittal sinus air after penetrating craniocerebral trauma. Surg Neurol 1986;25:276-8. 5. Navarrete ML, Galindo J, Pellicer M: Cavernous sinus air bubble. Ear Nose Throat J1990;69:771-2. 6. Orrell RW, Guthrie JA, Lamb JT: Nose-blowing and CSF rhinorrhoea. Lancet 1991;337:804. JClln Neuro-ophthalmol, Vol. 13, No. 1, 1993 |
