A Microanatomical Study On Transcranial Approach To The Orbit

Several surgical routes have been used to expose orbital lesions. The transcranialapproach is commonly selected for orbital tumors with intracranial extension, fortumors located in the orbital apex or/ and optic canal, and for intracranial tumorslocated in the superior and temporal compartment of the orbit and those in the lateralpart of the apex. Be familiar with orbital anatomy and microsurgical techniques,neurosurgeons could achieve optimal exposure and total removal of the tumors, withless complication via transcranial approach. This research will provide amicroanatomical understanding for transcranial-orbital surgery.Objective To provide microanatomical basis and parameters in detail fortranscranial approach to the orbit, and analyse the benefit as well as the risk of this.approach.Method The structure of orbit was dissected and measured under microscopein 15 formalin-fixed adult cadaver heads via trans-frontal approach, The anatomicalmarks related to this surgical approach were investigated, to obtain anatomicparameters, which would guide the procedures and avoid severe complications aspossible in the clinical operations. The distance between these landmarks wasmeasured, and the adjacent structures, blood supplying and their variations were alsorecorded. The date were analyzed with SPSS 10.0 software.Results The medial approach was directed through the space between thesuperior oblique and the levator palpebrae superior muscles. The medial approachwas selected for lesions locating in the medial part of the orbital apex, which exposedthe optic nerve from the globe to the optic canal. There were four structures(thetrochlear nerve, ophthahnic artery, nasociliary nerve, and superior ophthalmicvein)cross above the optical nerve to reach the medial part of the orbit. The averagedistances from the medial point with these structures cross above the optical nerve to the medial edge of the orbital end of the optic canal were 5.00±1.37mm,9.27±2.04mm, 10.66±1.98mm,and 19.33±1.59mm,respectively; The central approachwas directed through the space between the levator palpebrae superior and superiorrectus muscles. There were two variants of the central approach, the choice of whichdepended on whether the frontal nerve was retracted medially or laterally. The centralapproach was selected for lesions locating in the midpotion of the intraorbitalsegment of the optic nerve. The lateral approach was directed through the spacebetween the superior and the lateral rectus muscles. There were two variants of thelateral, the choice of which was determined by whether the superior ophthalmic veinis retracted medially or laterally. This approach was selected for lesions located in thesuperior, inferior or lateral part of the orbital apex as well as the superior orbitalfissure. The trochlear nerve, ophthalmic artery, nasociliary nerve, and superiorophthalmic vein cross above optical nerve with an average of 5.00±1.37mm,9.27±2.04mm, 10.66±1.98mm,and 19.33±1.59mm from the lateral point of thesestructures cross above the optic nerve to the lateral edge of the orbital end of the opticcanal, respectively. However, access to the deep apical area is limited because thesuperior ophthalmic vein blocks the line of view. The superior ophthalmic vein entersthe superior orbital fissure an average of 2.73±0.52mm lateral to the lateral edge ofthe superior orbital fissure.Conclusions There are various methods to enter the orbital space, howevernone of them can adapt to all conditions. We should select optimal approach for eachindividual case. This research provides a microanatomical foundation for avoidingthe damage of the important nerves and vessels in transcranial-orbital surgery.