The anatomical aspects of a surgical approach through the floor of the fourth ventricle

Abstract

In 1993 Kyoshima et al. introduced safe entry zones in the region of the 4th ventricle floor: infrafacial triangle and suprafacial triangle. Is it possible to demarcate these zones precisely in every case intra-operatively? A postmortem study of 40 brainstems of patients who had died of non-brain disease was performed to evaluate the degree of individual morphological and morphometrical variability of the 4th ventricle floor. The purpose of this study was to find constant landmarks and distances within the rhomboid fossa region which would help a neurosurgeon to determine safe approach zones through the 4th ventricle floor to brainstem lesions. Several anatomical landmarks-median sulcus, obex, vestibular area, vagal triangle, hypoglossal triangle-were found to be sufficiently visible in all examined brainstems. However, the facial colliculus which is a border structure between the infrafacial and suprafacial safe approach zone was poorly visible in about 37% of the analyzed material. The striae medullares were not found to be good orientation structures as they were not visible in 30% of the material and exhibited individual variability of a high degree in relation to their number and arrangement. In the morphometrical study analyzed measurements were taken by utilizing the digital image analyzer MULTISCAN. Based on the results obtained the authors suggest new borders of the infrafacial safe approach zone and morphometrical directions to determine the suprafacial safe approach zone in cases when the facial colliculus is not clearly visible or invisible intra-operatively.

Inter- and intra-patient variability of facial nerve response areas in the floor of the 4th ventricle

“…The observed large asymmetries are at variance with an anatomical study on healthy brainstems, which report a symmetric distribution of structures in the left and right rhomboid fossa. 15 This variability is most striking in patients of Group1 where the lesion did not distort the brainstem. In some patients of Group3 the asymmetry can be attributed to the proximity of the lesion, e.g.…”

“…4, [14][15][16][17] In a study based on 40 brainstems of patients who died of non-brain diseases, Bogucki et al 15 investigated the visibility of the different landmarks. The obex and the median sulcus were well identifiable in all specimens, but the facial colliculus was only poorly visible in 38% and the medullary striae were even invisible in 30% of the analyzed brainstems.…”

“…The obex and the median sulcus were well identifiable in all specimens, but the facial colliculus was only poorly visible in 38% and the medullary striae were even invisible in 30% of the analyzed brainstems. 15 The high variability of these structures renders them unreliable as landmarks for brainstem nuclei identification.…”

Morphometrische Studie zur Optimierung der Implantationstechnik zentraler H�rprothesen

“…1a, b dargestellten Distanzen a bis i wurden folgende Werte ermittelt: Sulcus medianus; N. VIII: N. vestibulocochlearis. Distanzen: a: Sulcus medianus -medialer Rand des Nucleus cochlearis ventralis, b: Sulcus medianus -lateraler Rand des Nucleus cochlearis ventralis, c: Sulcus medianus -medialer Rand des Nucleus cochlearis dorsalis, d: Sulcus medianus -lateraler Rand des Nucleus cochlearis dorsalisMittelwerte und Spannweite der Einzelmaße der Weite des Luschka-Foramen, Distanzangaben in cmH ie r st e h t e in e A n ze ig e Th is is a n a d ve rt is e m e n t Der in der vorliegenden Studie gewonnene Mittelwert von 2,42 cm war annä-hernd identisch mit Untersuchungsergebnissen von Lang et al[13] und Bogucki et al[1]. Gegenüber Matsushima et alNach der Literatur variierten Ausprägung und Ausrichtung in unterschiedlichster Weise[1,13].…”

“…Distanzen: a: Sulcus medianus -medialer Rand des Nucleus cochlearis ventralis, b: Sulcus medianus -lateraler Rand des Nucleus cochlearis ventralis, c: Sulcus medianus -medialer Rand des Nucleus cochlearis dorsalis, d: Sulcus medianus -lateraler Rand des Nucleus cochlearis dorsalisMittelwerte und Spannweite der Einzelmaße der Weite des Luschka-Foramen, Distanzangaben in cmH ie r st e h t e in e A n ze ig e Th is is a n a d ve rt is e m e n t Der in der vorliegenden Studie gewonnene Mittelwert von 2,42 cm war annä-hernd identisch mit Untersuchungsergebnissen von Lang et al[13] und Bogucki et al[1]. Gegenüber Matsushima et alNach der Literatur variierten Ausprägung und Ausrichtung in unterschiedlichster Weise[1,13]. Die Ergebnisse der eigenen Studie bestätigten diese Variabilität und zeigten, dass sich die Striae daher nicht als anatomische Landmarke eignen.Die Studie beweist durch morphometrisch ermittelte Werte eine eindeutige Beziehung zwischen der Lage des Nucleus cochlearis dorsalis und dem Tuberculum acusticum, was in bisherigen Veröf-fentlichungen[19,20,25] vermisst wird.…”