[Measurement and clinical significance of the posterior cranial fossa volume of patients with hemifacial spasm].
The etiology of hemifacial spasm had long been obscure until 1962 when Gardner proved that this hyperdysfunction of the facial nerve was caused by mechanical compression of the facial nerve by vascular structures in the posterior cranial fossa. In 1977, Jannetta proposed a specific location at the root entry zone of the facial nerve; this area has consequently been considered to be especially vulnerable to minor trauma such as vascular compression. In patients with hemifacial spasm, the posterior cranial fossa cavity is commonly found to be small or shallow on plain craniogram; this anatomical change in the skull is regarded as pathognomonic for the facial nerve hyperdysfunction. To make a quantitative analysis of the posterior cranial fossa volume in these patients, the following method was used. In the preliminary study, a dry human skull with an artificial "tentorium" made of thick paper was prepared to decide the fundamental plane for volume measurement by CT scan. This plane included attachments of posterior clinoid ligaments, superior petrosal veins and lateral sinuses. When this fundamental plane was projected to the lateral view on CT scan, it appeared to be almost identical to the line connecting the tip of posterior clinoid process to the internal occipital protuberance (the fundamental line). A horizontal CT scan for an intracranial volume measurement was performed in a parallel fashion to this fundamental line, with a 5 mm slice for the infratentorial and a 10 mm slice for the supratentorial area. The intracranial area of each horizontal slice was calculated by computed planimeter.(ABSTRACT TRUNCATED AT 250 WORDS)
D002508:Cephalometry; D003388:Cranial Fossa, Posterior; D005152:Facial Muscles; D005260:Female; D006801:Humans; D008297:Male; D012886:Skull; D013035:Spasm / Q000000981:diagnostic imaging / Q000209:etiology* / Q000473:pathology; D014057:Tomography, X-Ray Computed