Surgical approaches to the brain stem.

During the last decade there has been a remarkable increase in the interest of neurosurgeons in surgical approaches along the base of the skull. A plethora of different approaches, most of which involve a slight variation of a previously described approach, have been reported in the recent literature, frequently with proprietary claims of originality. This increased confidence of the neurosurgeon in approaching lesions along the base is due to our renewed interest in the anatomy of the skull base and our willingness to collaborate with some of our colleagues in otorhinolaryngology who have concentrated their surgical anatomic studies in this area for years. It is clear that the neurosurgeon who currently undertakes surgery of complex lesions involving the base of the skull, the brain stem and the associated cranial nerves and arteries must have a thorough understanding of this anatomy and frequently must engage the help of an ear-nose-and-throat colleague to enhance his or her own expertise with these complex cases. The emerging principle is that whenever possible, exposure should be obtained through carefully planned bone removal along the base rather than through brain retraction. It needs to be emphasized, however, that most of the complex approaches alluded to in the preceding sections are necessary only when the surgeon is dealing with extrinsic lesions, neoplastic or vascular, that only secondarily affect the brain stem itself. Almost all intrinsic lesions of the brain stem can be accessed through one of the more traditional approaches with which all neurosurgeons should be fully familiarized. When the lesion involves or points toward the floor of the fourth ventricle, a standard suboccipital approach through the vermis suffices. Lesions presenting in the cerebellopontine angle or the lateral pons may be safely approached through a standard retromastoid craniectomy. A more direct (perpendicular) access can be obtained by a standard subtemporal-transtentorial approach when the lesion is high and lateral, by a combined subtemporal-suboccipital approach when the lesion extends more inferiorly, and by a combined subtemporal-presigmoid approach for the more anteriorly located lesions. Anterior or anterolateral lesions of the highest aspect of the pons or of the mesencephalon can be readily accessed by the pterional-anterior temporal approach or by a standard subtemporal approach. Dorsal mesencephalic lesions require a supracerebellar/infratentorial approach or, when they extend more inferiorly, an occipital transtentorial approach. When the ventral aspect of the lower brain stem is involved, the lateral suboccipital approach works well.(ABSTRACT TRUNCATED AT 400 WORDS)