Midline Transcranial Approaches
When accessing the lamina terminalis via an anterolateral approach, the angle of attack and surgical view into the third ventricle are oblique and the surgeon has a blind spot of the ipsilateral wall of the third ventricle. The working corridor of the lamina terminalis can be better maximized by converting to a midline transcranial approach (bifrontal transbasal approach or frontobasal interhemispheric approach).[43,44] This offers the major advantage of direct midline orientation and access to the lamina terminalis with clear visualization and control of both walls of the third ventricle and the hypothalamus as well as the interpeduncular cistern (Figs. 4 and 5). In addition, access to the prechiasmatic space and both opticocarotid and carotid-oculomotor cisterns is readily achieved. For tumors residing in the retrochiasmatic space that extend up into the third ventricle, the lamina terminalis is opened to access and remove the tumor. Although direct visualization of the foramen of Monro is not possible, tumors extending superiorly at this level can be readily delivered through the midline trans–lamina terminalis approach. However, with a transbasal view from above, the undersurface of the optic chiasm and nerves cannot be visualized directly and remains a blind spot for residual tumor. Blind dissection of this region can also risk injury to the perforating vessels feeding the optic apparatus.
Modified one-piece extended transbasal approach. A: Patient in supine position with head of bed elevated about 30° to facilitate venous drainage, and with slight neck extension to allow the frontal lobes to fall away from the skull base. B: Planned bicoronal incision. C: Harvest of vascularized pedicled pericranial flap. D and E: The bifrontal bone flap incorporates the anterior wall of the frontal sinus so that the lowest basal trajectory to the floor of the anterior fossa is achieved without additional removal of the supraorbital bar. The dotted line (E) shows that the exposure is flush with the contour of the anterior skull base in the coronal plane without any obstruction of line of sight. F: Dural opening at the frontal base with ligation and division of the superior sagittal sinus.
Introperative photographs from illustrative Case 2 (A–D), in which a modified one-piece extended transbasal approach was used, and from a case (E and F) in which an anterolateral (supraorbital) approach was used. A: Subfrontal exposure optic chiasm and lamina terminalis (asterisk). B: Retrochiasmatic craniopharyngioma is removed via the trans–lamina terminalis corridor. C: Access is achievable via the lamina terminalis and prechiasmatic space. However, the blind spot is directly beneath the optic nerves and chiasm (shaded area). D: In a midline transbasal approach, the surgeon has control of both ependymal walls of the third ventricle and hypothalamus. E and F: In an anterolateral approach, such as the supraorbital approach seen here, access to the lamina terminalis (asterisk) is oblique. The major disadvantage is that the surgeon has good control and visualization of only the contralateral third ventricular wall but is blinded to the ipsilateral wall.
This approach is favorable for large midline retrochiasmatic craniopharyngiomas that are situated higher on the vertical hypophyseal axis with extension up into the third ventricle, especially in cases where the working corridor between the optic chiasm and the diaphragma sellae (infrachiasmatic window) is narrow and not favorable for an EEA (Fig. 6). Although there exist several variations of midline transcranial approaches based on orbitonasal osteotomies, we favor a modified one-piece extended transbasal approach,[43,44] described below. This involves a bifrontal craniotomy that incorporates the anterior wall of the frontal sinus so that the lowest basal trajectory to the floor of the anterior fossa is achieved without removal of the supraorbital bar as a separate osteotomy. With this approach, either a subfrontal or interhemispheric route can be used to access the lamina terminalis.
Illustrative Case 2 imaging. A–C: Preoperative sagittal (A) and coronal (B and C) postgadolinium T1-weighted MR images demonstrating a large retrochiasmatic craniopharyngioma compressing the optic chiasm. The tumor is located above the pituitary stalk (C, white arrow) and extends superiorly into the third ventricle. D and E: Postoperative sagittal (D) and coronal (E) postgadolinium T1-weighted MR images obtained after gross-total resection via a transbasal trans–lamina terminalis approach. F: Sagittal T2-weighted MR image shows that the lamina terminalis corridor (thicker white arrow), between the optic chiasm (white dot) and anterior communicating artery, is larger than the infrachiasmatic corridor (thinner white arrow), between the optic chiasm (white dot) and the top of the pituitary gland.
Modified One-piece Extended Transbasal Approach: Technical Pearls and Clinical Case Correlates
The patient is positioned supine with the head elevated approximately 30° to facilitate venous drainage (Fig. 4A). The head is extended slightly to allow the frontal lobes to fall away from the skull base. Lumbar catheter drainage can be used if additional CSF drainage is anticipated for further brain relaxation. Alternatively, an external ventricular drain can also be used in cases of preexisting obstructive hydrocephalus. A bicoronal incision (Fig. 4B) is made through the galea behind the hairline with care taken not to incise the pericranium, which is left adherent to the skull. The scalp is then elevated in a 2-layer fashion with the galeocutaneous layer elevated first followed by elevation of the vascularized pedicled pericranial flap as a separate layer (Fig. 4C). The galea is undermined posterior to the skin incision to increase the length and surface area of the pericranial flap. Care is taken to preserve the supraorbital neurovascular bundle at the supraorbital notch so as not to compromise the vascular supply to the pericranial flap. Interfascial dissection of the temporalis muscle is performed to protect the frontalis branch of the facial nerve bilaterally.
Next, a modified one-piece extended transbasal approach is performed.[43,44] This is essentially a bifrontal bone flap that incorporates the anterior wall of the frontal sinus so that the inferior osteotomy is flush with the contour of the anterior skull base in the coronal plane (Fig. 4D and E). The midline inferior cut is at the level of the nasion, and the lateral cuts are at the level of the orbital roofs. An osteotome is used to cut the intersinus septum in the frontal sinus to disconnect the bone flap from the skull. The bone flap is then removed using a fracture technique. The frontal sinus is then exenterated, cranialized, and sealed off with betadine-soaked Gelfoam pledgets. The orbital roofs are then flattened with a high-speed drill, thereby providing a basal exposure of the anterior skull base without any bony overhang that can obstruct the line of site to the cribriform plate and the lamina terminalis. This technique obviates the need for any additional supraorbital bar removal. The dura is opened transversely along the frontal base and the superior sagittal sinus is ligated and divided near the crista galli to avoid complications of venous infarction (Fig. 4F). The falx cerebri is then incised to the free edge to expose the interhemispheric fissure.
At this juncture, either an interhemispheric route or a subfrontal route can be chosen. For an interhemispheric route, the arachnoid of the interhemispheric fissure is divided sharply under microscopic visualization to identify the pericallosal arteries, anterior communicating artery complex, optic chiasm, lamina terminalis, olfactory tracts, and cribriform plate. Alternatively, a subfrontal exposure can be performed by elevating the right frontal lobe while avoiding retraction on the contralateral frontal lobe. It is important to dissect the arachnoid off of both olfactory tracts so that they are not avulsed from the cribriform plate during frontal lobe elevation. We also recommend placing moist Biocol collagen pledgets (Codman) over the olfactory bulbs and tracts to prevent dessication and injury during the surgery.
The lamina terminalis is identified and opened sharply (Fig. 5). Initially, the floor of the third ventricle is identified and further incised to expose tumors in the retrochiasmatic space that have elevated the floor of the third ventricle superiorly. In craniopharyngiomas that have invaded into the third ventricle or are purely intraventricular, the tumor will be visible after the lamina terminalis is opened. Intratumoral debulking with an ultrasonic aspirator may be needed in patients with large tumors to collapse the tumor. Careful extracapsular dissection is then performed by peeling the tumor off of the ependymal walls of the third ventricle and hypothalamus. Tumors with superior extension toward the foramen of Monro can be brought down carefully and delivered through the lamina terminalis window. As the tumor is dissected along its posteroinferior margin, the mammillary bodies are encountered and the tumor is dissected away from the membrane of Liliequist. It is best to preserve the integrity of the membrane of Liliequist since this aids in protection of the basilar artery, posterior cerebral arteries, and P1 perforators.[43,44]
One major disadvantage with this approach is the lack of direct visualization of the undersurface of the optic nerves and chiasm (blind spot), and therefore, one cannot perform accurate dissection of tumor adhesions in this area (Fig. 5C). Although angled endoscopes and dental mirrors may aid in visualization, blind dissection can increase the risk of injury to the optic apparatus. Moreover, the lamina terminalis can sometimes be a limited working corridor, which can result in more manipulation of the optic apparatus when dissecting larger tumors. Therefore, it is important to sequentially debulk the tumor to smaller sizes so that it can be safely delivered through the lamina terminalis corridor. Lastly, some degree of brain retraction is involved with this approach. Therefore, it is important to drain CSF from the cisterns for adequate brain relaxation.
At the time of closure, it is important to obtain a watertight dural closure as much as possible. The exposed frontal sinuses have been previously packed off with betadine-soaked Gelfoam pledgets at the time of the craniotomy (see above). Alternatively, a fat graft can be used here as well. The pericranial flap is then rotated over the obliterated frontal sinuses to provide a vascularized barrier between the intra- and extracranial contents. The redundant distal portion of the pericranial flap is rotated over the dural closure. We do not routinely use postoperative lumbar drainage for transbasal cases.
Illustrative Case 2: Transbasal Trans–Lamina Terminalis Approach for Retrochiasmatic Craniopharyngioma. This 52-year-old man presented with progressive headaches, a 40-pound weight gain over 6 months due to an increased appetite, and bitemporal hemianopsia. MRI demonstrated a large retrochiasmatic retroinfundibular, mixed solid and cystic craniopharyngioma (Fig. 6). We initially proposed an EEA to remove the tumor because of the advantages of better visualization of the retrochiasmatic region and hypothalamus with an approach coming from below. However, after careful review of the MR images, we felt that exposure via an EEA would be limited because of the narrow infrachiasmatic operating window between the optic chiasm and the diaphragma sellae (Fig. 6F). Instead, we chose the transbasal subfrontal trans–lamina terminalis approach because of a wider and more favorable corridor between the optic chiasm and the anterior communicating artery via the lamina terminalis (Video 1).
VIDEO 1. Illustrative Case 2. Video clip showing removal of retrochiasmatic craniopharyngioma using transbasal trans–lamina terminalis approach. Copyright James K. Liu. Published with permission. Click here to view.
By approaching the tumor with a midline approach instead of an anterolateral approach, we had control of both walls of the third ventricle and hypothalamus (Fig. 5D). The major limitation was the blind spot underneath the optic chiasm and nerves, as mentioned above. A gross-total resection was achieved, and the patient remained neurologically intact with stable vision.
Illlustrative Case 3: Combined Transbasal and Endoscopic Endonasal Approach. This 19-year-old woman presented with progressive headaches, visual loss, nausea, and vomiting. MRI demonstrated a giant multicystic craniopharyngioma occupying the suprasellar and anterior skull base region, and also in the retrochiasmatic third ventricular region with obstructive hydrocephalus (Fig. 7). Because the tumor had significant interhemispheric extension with encasement of the pericallosal arteries, and also lateral extension with encasement of the left middle cerebral artery, we felt that the safest approach to resect the greatest amount of tumor with excellent vascular control was a transbasal interhemispheric approach with additional access through the lamina terminalis corridor to remove the retrochiasmatic third ventricular component.
Illustrative Case 3. A–C: Preoperative coronal (A), sagittal (B), and axial (C) postgadolinium T1-weighted MR images demonstrating a giant multicystic craniopharyngioma occupying the suprasellar and anterior skull base region and also in the retrochiasmatic third ventricular region, with obstructive hydrocephalus. There is also significant interhemispheric extension with encasement of the pericallosal arteries (B, white arrow) and lateral extension with encasement of the left middle cerebral artery (C, double white arrows). A transbasal interhemispheric trans–lamina terminalis approach was performed. D–F: Corresponding postoperative images showing approximately 95% removal of the tumor. There was residual tumor adherent to the infrachiasmatic region, hypothalamus, and microscopic residue on portions of the pericallosal arteries.
A modified one-piece extended transbasal approach was performed. The anterior cyst in the interhemisheric fissure was carefully dissected away from the engulfed pericallosal arteries (Fig. 8). Near-total resection of the anterior cyst was achieved, leaving small microscopic remnants adherent to some portions of the pericallosal arteries. The lamina terminalis was then opened to remove the retrochiasmatic cyst. Unfortunately, the working corridor was found to be somewhat narrow. Near-total resection was achieved, leaving a small remnant adherent to the hypothalamus and to the undersurface of the optic chiasm.
Illustrative Case 3 intraoperative photographs of transbasal interhemispheric trans–lamina terminalis approach. A: Interhemispheric dissection shows cystic tumor (T) engulfing pericallosal A3 vessels. B: Tumor (T) has been carefully dissected away from the anterior communicating artery (Acom), perforators (AP), A1, A2, and recurrent artery of Heubner (Hb). The remaining retrochiasmatic tumor is hidden behind the lamina terminalis (T*). C: The lamina terminalis is opened posterior to the optic chiasm (OC) to access the tumor (T*). D: Final view after decompression of the optic chiasm and nerves.
Postoperative MRI showed greater than 95% removal of the tumor with excellent decompression of the optic chiasm and resolution of hydrocephalus (Fig. 7D–F). The patient had restoration of normal vision with normal pituitary function. At 3 months after surgery, she presented with progressive headaches and worsening vision due to recurrence of the retrochiasmatic cyst with extension into the third ventricle (Fig. 9). This time, an endoscopic endonasal transplanum transtuberculum approach was performed to access the cyst in the retrochiasmatic space (Fig. 10). The endonasal corridor was noted to be wider than the lamina terminalis corridor, with better inferior-to-superior visualization of the infrachiasmatic region, hypothalamus, and third ventricle. The pituitary stalk was expanded by the tumor and not salvageable. A near-complete tumor removal was achieved, leaving a densely calcified remnant that was adherent to the undersurface of the optic chiasm. Postoperatively, the patient had restoration of normal vision and was maintained on hormone replacement therapy. She underwent additional fractionated radiation therapy to the residual adherent tumor and has remained recurrence free for 2 years.
Illustrative Case 3 imaging. A and B: Postoperative sagittal and coronal postgadolinium T1-weighted MR images obtained at 3 months' follow-up showing recurrence of retrochiasmatic cystic craniopharyngioma extending into the third ventricle. An endoscopic endonasal transplanum transtuberculum approach was performed to resect the tumor. Near-total resection was achieved, leaving a calcified remnant adherent to the undersurface of the optic chiasm. C and D: Corresponding postoperative MR images obtained 3 months after EEA showing stable residual enhancement of microscopic tumor that was adherent to critical structures.
Illustrative Case 3 intraoperative photographs obtained during second-stage EEA resection of recurrent cystic craniopharyngioma in the retrochiasmatic space. A: The cyst is decompressed and dissected away from the undersurface of the optic chiasm (OC). B and C: Tumor capsule (T) is removed from the retrochiasmatic space. D: After removal of the tumor, the third ventricle (3V) is visualized. Residual calcified tumor (asterisk) is densely adherent to the undersurface of the optic chiasm (OC). E: Endoscopic view of the third ventricle shows both foramen of Monro. F: Reconstruction of skull base with nasoseptal flap (NSF).
This case illustrates the importance of having multiple operative approaches in the surgical armamentarium for craniopharyngioma treatment. The initial transbasal approach was chosen because it provided safer dissection of the engulfed pericallosal arteries and left middle cerebral artery. The diameter of the lamina terminalis working corridor is variable depending on the patient. Unfortunately, it was rather narrow in this particular patient and resulted in residual tumor that progressed with recurrence. However, this limitation was adequately addressed using an extended EEA.
Neurosurg Focus. 2016;41(6):e5 © 2016 American Association of Neurological Surgeons