Microsurgical anatomy of the orbital apex and principles of transcranial orbital exploration.

Although many problems may present with unilateral proptosis, a careful clinical investigation can narrow the differential diagnosis to those problems which can be treated best by the neurosurgeon. The primary indication for transcranial exploration is when the pathological process is found to involve both the orbit and the cranial cavity as in all cases of optic nerve glioma, orbital meningioma, encephalocele, and some mucoceles, hemangiomas, aneurysmal bone cysts, and ossifying fibromas. Transcranial exploration may also be indicated for some tumors which crowd the orbital apex, such as, neurofibromas and osteomas; tumors in this location can be more widely exposed and safely dealt with by this route. A prime objective in these cases, however, must be preservation of function with a good cosmetic result. It is of equal importance to be aware that many conditions producing exophthalmos can be cured by direct orbital exploration, radiotherapy, or medical management. Malignant orbital tumors should never be exposed to the cranial cavity by transcranial exploration, whereas, radical exenteration may be curative in some carefully studied cases. Accuracy in clinical diagnosis and the proper selection of treatment modality for conditions in the orbit requires a clear understanding of this regional anatomy. I hope that this brief review of the pertinent microsurgical anatomy of the orbital apical region has helped to substantiate a strong neurosurgical claim to all primary optic nerve tumors; and, incidentally, I hope it provides an explanation for why I sent so many other patients back to Dr. Algernon Reese with the recommendation that transcranial surgery did not seem indicated. The success of this attitude may be attested to by the fact that we performed no unnecessary craniotomies nor did we pass by problems which would have best been treated by transcranial orbital exploration.