Pakrit Jittapiromsak, Pushpa Deshmukh, Peter Nakaji, Robert F. Spetzler and Mark C. Preul
The standard superior craniotomy approach through the orbital roof is obstructed by numerous muscles, nerves, and vessels. Accessing the medial intraconal space also involves considerable brain retraction. The authors present a modified approach through the frontal sinus that overcomes these limitations.
Seven fixed silicone-injected cadaveric specimens were dissected bilaterally. In addition to the superior orbital wall, the ethmoidal sinuses and medial orbital wall were removed. The anatomical relationships between the major neurovascular complexes in the medial intraconal space and the optic nerve were observed.
Intraconally, working space was created both in a “superior window” between the superior oblique and levator palpebrae muscle and in a “medial window” between the superior oblique and medial rectus muscle. The superior window mainly created an ipsilateral trajectory to the deep target. The medial window, which created a contralateral trajectory, provided a more inferior view of the medial intraconal space. Removal of the medial orbital wall further widened the exposure obtained from the superior window. The combination of these working windows makes the medial surface of the optic nerve available for exploration from multiple angles. Most of the major neurovascular complexes of the posterior orbit can be retracted safely without impinging on the optic nerve.
This novel extradural transfrontoethmoidal approach affords a direct view to the medial posterior orbit without major conflicts with intraconal neurovascular structures and requires minimal brain manipulation. The approach appears to offer advantages for medially located intraconal lesions.
Sam Safavi-Abbasi, Joseph M. Zabramski, Pushpa Deshmukh, Cassius V. Reis, Nicholas C. Bambakidis, Nicholas Theodore, Neil R. Crawford, Robert F. Spetzler and Mark C. Preul
The authors quantitatively assessed the effects of balloon inflation as a model of tumor compression on the brainstem, cranial nerves, and clivus by measuring the working area, angle of attack, and brain shift associated with the retrosigmoid approach.
Six silicone-injected cadaveric heads were dissected bilaterally via the retrosigmoid approach. Quantitative data were generated, including key anatomical points on the skull base and brainstem. All parameters were measured before and after inflation of a balloon catheter (inflation volume 4.8 ml, diameter 20 mm) intended to mimic tumor compression.
Balloon inflation significantly shifted (p < 0.001) the brainstem and cranial nerve foramina (mean [± standard deviation] displacement of upper brainstem, 10.2 ± 3.7 mm; trigeminal nerve exit, 6.99 ± 2.38 mm; facial nerve exit, 9.52 ± 4.13 mm; and lower brainstem, 13.63 ± 8.45 mm). The area of exposure at the petroclivus was significantly greater with balloon inflation than without (change, 316.26 ± 166.75 mm2; p < 0.0001). Before and after balloon inflation, there was no significant difference in the angles of attack at the origin of the trigeminal nerve (p > 0.5).
This study adds an experimental component to the emerging field of quantitative neurosurgical anatomy. Balloon inflation can be used to model the effects of a mass lesion. The tumor simulation created “natural” retraction and an opening toward the upper clivus. The findings may be helpful in selecting a surgical approach to increase the working space for resection of certain extraaxial tumors.
Eberval Gadelha Figueiredo, Joseph M. Zabramski, Pushpa Deshmukh, Neil R. Crawford, Mark C. Preul and Robert F. Spetzler
The management of wide-necked, giant, or unsuccessfully coil-treated basilar apex aneurysms requires a wide exposure, for both working area and linear visualization of the basilar artery (BA). Cranial-based approaches, such as the transcavernous approach, have been proposed to deal with such aneurysms; whether abbreviated forms of this approach might provide similar exposure remains controversial. The authors examine this issue quantitatively.
Four alcohol-preserved cadaveric heads injected with pigmented silicone were prepared for bilateral dissection. After completing an orbitozygomatic craniotomy, the surgeons worked in a reverse direction, performing the transcavernous approach in five steps: 1) posterior clinoidectomy; 2) cavernous sinus opening; 3) anterior clinoidectomy; 4) cutting of the distal dural ring; and 5) cutting of the proximal dural ring.
Performing the complete transcavernous approach significantly increased the working area and linear exposure of the BA compared with abbreviated forms of the approach (p < 0.05). Opening the roof of the cavernous sinus significantly increased the working area compared with posterior clinoidectomy alone (p = 0.014); however, additional gains in exposure required completing the transcavernous approach. Resection of the anterior clinoid process combined with opening of only the distal dural ring did not significantly increase the working area or linear exposure of the BA.
The complete transcavernous approach significantly increases the working area and linear exposure of the BA compared with the more conservative forms of approach.
Rungsak Siwanuwatn, Pushpa Deshmukh, Eberval Gadelha Figueiredo, Neil R. Crawford, Robert F. Spetzler and Mark C. Preul
The authors quantitatively assessed the working areas and angles of attack associated with retrosigmoid (RS), combined petrosal (CP), and transcochlear (TC) craniotomies.
Four silicone-injected cadaveric heads were bilaterally dissected using three approaches progressing from the least to the most extensive. Working areas were determined using the Optotrak 3020 system on the upper and middle thirds of the petroclivus and brainstem. Angles of attack were studied using the Elekta SurgiScope at the Dorello canal and the origin of the anterior inferior cerebellar artery (AICA).
The TC approach provided significantly greater (p < 0.001) working areas at the petroclivus (755.6 ± 130.1 mm2) and brainstem (399.3 ± 68.2 mm2) than the CP (354.1 ± 60.3 and 289.7 ± 69.9 mm2) and RS approaches (292.4 ± 59.9, 177.2 ± 54.2 mm2, respectively). The brainstem working area associated with the CP approach was significantly larger (p < 0.001) than that associated with the RS route. There was no difference in the petroclival working area comparing the CP and RS approaches (p = 0.149). The horizontal and vertical angles of attack achieved using the TC approach were wider than those of the CP and RS at the Dorello canal and the origin of the AICA (p < 0.001).
The CP approach offers a more extensive working area than the RS for lesions involving the anterolateral surface of the brainstem, but not for petroclival lesions. The TC approach provides the widest corridor, improving the working area and angle of attack to both areas, but hearing must be sacrificed and the facial nerve is at risk.