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Bilateral Cerebellopontine Angle Air-CT Cisternography

Seungho H. Lee," 2 Errol Lewis, ' Jaime H. Montoya,' and Jere F. Seelaus'

Recently, new methods in the workup of cerebellopontine air does not rise above th e CPA cistern . The plane of secti on angle (CPA) tumors have been establi shed. These include is parallel to th e canthomeatal line, and consecutive and computed tomography (CT) in combination with intravenous overl apping 8 mm sections are obtained ceph alad from a injection of contrast material [1], enhancement of cerebro­ line 1 cm below the canthomeatal line. Scanning is contin­ spinal fluid with metrizamide [2], and most recently air-CT ued until the intern al auditory canal and CPA cistern being cisternography [3, 4]. We describe a simple technique for examined are completely vi sualized (fig. 1 A) . examining both cerebellopontine angles with one lumbar Depending on th e amount of air already trapped, an puncture using air-CT cisternography. Eight of 10 attempts additional 2-3 ml may be introduced. The spinal needle is were successful. th en removed and th e patient is ready to be turned into th e opposite lateral decubitus position to examine the opposite CPA cistern . Initially, the pati ent is pl aced in the supine Method position while the head and sli ghtly fl exed chin are fi xed The patient lies on the CT table in the lateral decubitus with both hands of the examiner. Then th e head is rapidly position with the " suspected " side up. A lumbar puncture rotated to the opposite saggital plane with no undue move­ is performed with a 20 gauge spinal needle and 3-4 ml of ment. The air previously trapped on one side may now spinal fluid is obtai ned. Air (5-6 ml) is slowly injected with collect in the opposite CPA cistern vi a th e prepontine cistern the head elevated 15° either by tilting th e tabl e or elevating (fig. 18). Once the patient is lying in the opposite position, the shoulder and head, so that the air may coll ect in the scanning is repeated as described (fig. 1 C). cerebellopontine angle (CPA) cistern of interest. The pati ent feels a slight tension behind th e ear wh en the air coll ects in Discussion the CPA cistern. Then, with the pati ent in the lateral decu­ bitus position, the saggital plane of the head is pl aced Earl y diag nosis of small acoustic neuromas is essential to parallel to the table, or a slightly lower position, so that the minimize the postoperati ve mortality and the morbidity [5].

Fi g. 1.-A, Small acoustic neuroma ( arrow) in entra nce of right intern al au­ ditory canal, with air in cerebellopontine angle cistern . B, Ai r ( arrow) in prepon­ tin e cistern . C, Air ( arrow) in normal internal auditory canal. A

Received June 11 , 1980; accepted after revision July 8 , 1980. ' Department of Radiology, Temple University Health Sciences Center, 3401 N. Broad St., Ph il ad elphia, PA 19 140 . 2Present address: Department of Radiology, State University of New Yo rk, Upstate Medical Center, Syracuse, NY 13210. Address reprint requests to S. H. Lee. AJNR 2:105-106, January/ February 1981 0 1 95- 6 1 08 / 8 1/ 0021-0 1 05 $00.00 © Am eri can Roentgen Ray Society 106 LEE ET AL. AJNR:2, January / February 1981

Both cerebellopontine angle cisterns and internal auditory 2. Dubois P, Drayer BP. An evaluation of current diagnostic canals mu st be examined not only for comparison purposes, radiologic modalities in the investigation of acoustic neurilem­ but also for detection of bilateral lesions since 4% of acous­ momas. Radiology 1978; 1 26 : 1 73-1 79 tic tumors are bilateral ; often in patients with Von Reckling­ 3 . Sort/and O. Computed tomography combined with gas cistern­ ography for the diagnosis of expanding lesions in the cerebel­ housen disease [6]. This relatively small and painless pro­ lopontine angle. Neuroradiology 1979; 18: 19-22 cedure allows rapid examination of both CPA cisterns on 4. Kricheff I, Bergeron RT, Pinto RS , Cohen N. CT-air cisternog­ one occasion. raphy and canalography in the diagnosis of small acoustic ACKNOWLEDGMENTS neuromas. Am J Neuroradiol 1980; 1 : 57 -63 5 . Buchheit WA , Johnson CH. Surgica l removal of acoustic neu­ We th ank Milne Hewish and Connie Presser for assistance in romas. In : Schmidek HH, Swett WH , eds. Current techniques manuscript preparation . in operative neurosurgery. New York: Grune & Stratton, 1977: 8 7-100 REFERENCES 6. Pantmann M, Stevkens JM, Ch ancachan R. et al. Th e internal 1. Paxton R, Ambrose J. The EMI scanner; a brief review of 650 auditory meatus: anatomy, pathology. and surgery. Edinburgh: patients. Br J Radiol 1974;47 :530-565 Churchill Livingstone. 1975