Noninvasive detection of intracranial vascular lesions using an electronic stethoscope

Using an electronic stethoscope, the authors have attempted noninvasive detection of intracranial aneurysms, arteriovenous malformations (AVM's), and carotid cavernous fistulas in 45 patients. A microphone of older design and a newly designed horn-coupled probe microphone were used to record the sound signals emanating from the cranium. A trigger pulse recorded by another microphone placed over the carotid area or the precordium was used to time the intracranial signals. The sound signals were converted to electrical signals, amplified, filtered, and analyzed using fast Fourier transformation to give plots of amplitude versus frequency of the signals. A spike at a certain frequency or a bruit over a band of frequencies was considered a positive finding. The records of 18 of the patients were not satisfactory for analysis, mainly due to external noise interference. Eight of 11 aneurysm patients with satisfactory recordings emitted resonant spikes, turbulent bruits, or combinations of the two. The other three records were negative. Four patients with AVM's and two with carotid cavernous fistulas exhibited broad-band bruits representing turbulent flow. Neither spikes nor bruits were demonstrable in three patients with brain tumors or in seven patients without intracranial vascular lesions. Experimental vein pouch aneurysms were also induced in two dogs. Recordings from these animals revealed resonant spikes. The limitations and scope of electronic stethoscope audiometry are discussed.