Microsurgical Anatomy and Approaches around the Lateral Recess with Novel Safe Entry Zone into the Pons

Objective The lateral recess is a well-known structure communicating between the ventricle and cistern, which is exposed when treating lesions involving the fourth ventricle and the brainstem during surgeries, such as the transcerebellomedullary fissure approach. In this study, we examined the microsurgical anatomy around the lateral recess, including the fiber tracts, adjacent structure, as well as rhomboidal lip and advocated the possibility of a novel entry zone to the lower pons.

Methods Ten cadaveric heads were examined with microsurgical techniques, and two heads were examined with fiber dissection to clarify the anatomy between the lateral recess and adjacent structures. Twenty rhomboid lips were investigated. The lateral and medial routes of the transcerebellomedullary fissure approach were demonstrated.

Results The lateral recess was classified into medullary and cisternal segments. The extension of the rhomboid lip in the cerebellopontine cistern was classified into three types. The medial and lateral routes in the transcerebellomedullary fissure approach provided the wide access to the lateral recess. The floccular peduncle ran rostral to the lateral recess, and this region was considered to be a potential entry zone to the lower pons. By using appropriate either route, a medial to lateral or lateral to medial entry-axis provided wide exposure of the lower pons around the lateral recess.

Conclusion The medial and lateral routes of the transcerebellomedullary fissure approach provided wide exposure of the lateral recess. The incision around the floccular peduncle is a potentially new safe entry zone to the lower pons.