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Shigeaki Kobayashi, Kenichiro Sugita, Yuichiro Tanaka and Kazuhiko Kyoshima

✓ The authors present a new technique for surgery in the pineal region: a supracerebellar approach with the patient in the prone position. The surgeon sits on the left side of the patient, who lies prone with the head flexed and higher than the heart level (“Concorde position”). The main advantages of this arrangement over the sitting position include less fatigue on the part of the surgeon and decreased likelihood of air embolism. Fourteen patients have been operated on in this position. Pooling of blood in the operating field is rarely a problem.

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Kazuhiko Kyoshima, Shigeaki Kobayashi, Hirohiko Gibo and Takayuki Kuroyanagi

✓ Direct surgery for intra-axial lesions of the brain stem is considered a hazardous procedure, and morbidity of varying degrees cannot be avoided even with partial removal or biopsy. The main causes of morbidity relate to direct damage during removal of the lesion, selection of an entry route into the brain stem, and the direction of brain stem retraction. The authors examined the possibility of making a medullary incision and retracting the brain stem, taking into account the symptomatology and surgical anatomy, and found two safe entry zones into the brain stem through a suboccipital approach via the floor of the fourth ventricle. These safe entry zones are areas where important neural structures are less prominent. One is the “suprafacial triangle,” which is bordered medially by the medial longitudinal fascicle, caudally by the facial nerve (which runs in the brainstem parenchyma), and laterally by the cerebellar peduncle. The second is the “infrafacial triangle,” which is bordered medially by the medial longitudinal fascicle, caudally by the striae medullares, and laterally by the facial nerve. In order to minimize the retraction-related damage to important brain-stem structures, the brain stem should be retracted either laterally or rostrally in the suprafacial triangle approach and only laterally in the infrafacial triangle approach.

Three localized intra-axial brain-stem lesions were treated surgically via the safe entry zones using the suprafacial approach in two and the infrafacial approach in one. The cases are described and the approaches delineated. Both approaches are indicated for focal intra-axial lesions located unilaterally and dorsal to the medial lemniscus in the lower midbrain to the pons. Magnetic resonance imaging is useful in selecting these approaches, and intraoperative ultrasonography is helpful to confirm the exact location of a lesion before a medullary incision is made. These approaches can also be used as routes for aspiration of brain-stem hemorrhage as well as for tumor biopsy.

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Yuichiro Tanaka, Shigeaki Kobayashi, Kazuhiko Kyoshima and Kenichiro Sugita

✓ Experience with surgical clipping of 16 large and nine giant aneurysms of the intradural internal carotid artery (ICA) is described. Reconstruction of the parent artery with part of the aneurysmal wall was necessary in the majority of cases. Multiple clips were required for satisfactory clipping in 20 cases. Complications related to the clipping procedure comprised occlusion and stenosis of the parent carotid artery in isolated cases. Straightening of the parent carotid artery with consequent kinking of the middle cerebral artery was seen in three cases of an aneurysm with a dome directed ventrally in the proximal segment of the ICA. The factors that caused straightening of the ICA are analyzed. It was observed that an excessive change in the direction of the ICA can cause cerebral infarction.

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Susumu Oikawa, Kazuhiko Kyoshima and Shigeaki Kobayashi

Object

The authors report on the surgical anatomy of the juxtadural ring area of the internal carotid artery to add to the information available about this important structure.

Methods

Twenty sides of cadaver specimens were used in this study. The plane of the dural ring was found to incline in the posteromedial direction. Medial inclination was measured at 21.8š on average against the horizontal line in the anteroposterior view on radiographic studies. Posterior inclination was measured at 20.3š against the planum sphenoidale in the lateral projection, and the medial edge of the dural ring was located 0.4 mm above the tuberculum sellae in the same projection. The lateral edge of the tuberculum sellae was located 1.4 mm below the superior border of the anterior clinoid process. The carotid cave was situated at the medial or posteromedial aspect of the dural ring; however, two of the 20 specimens showed no cave formation. The carotid cave contained the subarachnoid space in 13 sides, the arachnoid membrane only in three sides, and the extraarachnoid space in two sides. The authors propose that the marker of the medial side of the dural ring, which is more proximal than the lateral, is the tuberculum sellae in the lateral view on radiographic studies. In the medial aspect of the dural ring the intradural space can be situated below the level of the tuberculum sellae because of the existence of the carotid cave.

Conclusions

The authors found that an aneurysm arising from the medial side of the juxtadural ring area even below the tuberculum sellae is a potential cause of subarachnoid hemorrhage.

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Susumu Oikawa, Kazuhiko Kyoshima and Shigeaki Kobayashi

Object. The authors report on the surgical anatomy of the juxta—dural ring area of the internal carotid artery to add to the information available about this important structure.

Methods. Twenty sides of cadaver specimens were used in this study. The plane of the dural ring was found to incline in the posteromedial direction. Medial inclination was measured at 21.8° on average against the horizontal line in the anteroposterior view on radiographic studies. Posterior inclination was measured at 20.3° against the planum sphenoidale in the lateral projection, and the medial edge of the dural ring was located 0.4 mm above the tuberculum sellae in the same projection. The lateral edge of the dural ring was located 1.4 mm below the superior border of the anterior clinoid process. The carotid cave was situated at the medial or posteromedial aspect of the dural ring; however, two of the 20 specimens showed no cave formation. The carotid cave contained the subarachnoid space in 13 sides, the arachnoid membrane only in three sides, and the extraarachnoid space in two sides. The authors propose that the marker of the medial side of the dural ring, which is more proximal than the lateral, is the tuberculum sellae in the lateral view on radiographic studies. In the medial aspect of the dural ring the intradural space can be situated below the level of the tuberculum sellae because of the existence of the carotid cave.

Conclusions. An aneurysm arising from the medial side of the juxta—dural ring area even below the tuberculum sellae is a potential cause of subarachnoid hemorrhage.

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Kazuhiko Kyoshima, Hirohiko Gibo, Shigeaki Kobayashi and Kenichiro Sugita

✓ A new method of cranioplasty is described in which the inner table of the bone flap obtained during craniotomy is used for grafting. The method was used in 10 cases to repair bone defects caused by a growing skull fracture in two, created during removal of an invasive skull tumor in two, during the approach to intraorbital tumors in two, and secondary to craniectomy for additional exposure in four. The method has the advantage that a piece of the inner table for grafting can be obtained from the craniotomy bone flap, without the need for an additional skin incision or taking a graft from another part of the body, and foreign-body reaction is minimal.

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Kenichiro Sugita, Shigeaki Kobayashi, Kazuhiko Kyoshima and Fukuo Nakagawa

✓ Twenty-four different kinds of fenestrated clips are introduced for the obliteration of unusual aneurysms. The clips were used for eight aneurysms of the internal carotid artery and 10 aneurysms of the vertebral artery. All but one of the aneurysms were successfully obliterated. Recommendations are made concerning the actual use of the clips.

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Kazuhiko Kyoshima, Susumu Oikawa and Shigeaki Kobayashi

✓ The authors report two cases in which the ophthalmic artery (OA) originated from the interdural portion of the internal carotid artery at the carotid dural ring and coursed within the dura. This configuration was observed during surgeries performed in 82 cases of juxta—dural ring aneurysms.

In surgery for such an aneurysm, if the OA is not seen intradurally, an attempt should be made to find this kind of variation by using a Doppler flowmeter before sectioning the dural ring.

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Kazuhiko Kyoshima, Shigeaki Kobayashi, Kenji Wakui, Yoshiki Ichinose and Hiroshi Okudera

✓ A newly designed puncture needle for aspirating large or giant aneurysms is described. This puncture needle represents a modification of an intravenous catheter with an internal needle. It is designed to prevent blood from leaking when the internal needle is removed and has a lateral tube for aspiration. Following aneurysm puncture with the parent artery temporarily trapped, the catheter is positioned on the head frame with a brain spatula and a self-retaining retractor. Blood is suctioned through the lateral tube with a syringe or the suction system normally used in the operating room.

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Shigeaki Kobayashi, Kazuhiko Kyoshima, Hirohiko Gibo, Sathyaranjandas A. Hegde, Toshiki Takemae and Kenichiro Sugita

✓ In a series of 32 surgical cases of carotid-ophthalmic artery aneurysm, seven of the lesions were located in the “carotid cave.” This special type of aneurysm is usually small and projects medially on the anteroposterior view of the angiogram. At surgery, it is located intradurally at the dural penetration of the internal carotid artery (ICA) on the ventromedial side, appears to be buried in the dural pouch (carotid cave), and is often difficult to find, dissect, and clip. The aneurysm extends into the cavernous sinus space, and the parent ICA penetrates the dural ring obliquely. An ipsilateral pterional approach was used in all 32 cases, and ring clips were used exclusively because the aneurysms were located ventromedially. Clipping was successful in five cases. All patients returned to their preoperative occupation, although vision worsened postoperatively in two cases. The technical steps required for successful obliteration of this aneurysm are summarized as follows: 1) exposure of the cervical ICA; 2) unroofing of the optic canal and removal of the anterior clinoid process; 3) exploration of the ICA around the dural ring and opening of the cavernous sinus; 4) direct retraction of the ICA and optic nerve; and 5) application of multiple ring clips to conform to the natural curvature of the carotid artery; a curved-blade ring clip is especially useful. The relevant topographic anatomy is discussed.