Comparison of lateral microsurgical preauricular and anterior endoscopic approaches to the jugular foramen.

INTRODUCTION: This project compares access to the anterolateral part of the jugular foramen provided by the lateral microsurgical preauricular and the anterior endoscopic approaches, and defines the important landmarks involved in each approach. STUDY DESIGN: Cadaveric study. RESULTS: The endoscopic transnasal/transmaxillary transpterygoid corridor provides a less invasive route for selected lesions in the jugular foramen than the traditional open route through the preauricular subtemporal infratemporal fossa approach. However, the anterior endoscopic approach provides a smaller channel to the jugular foramen than the preauricular approach. CONCLUSIONS: The anterior endoscopic approach to the anterolateral part of the jugular foramen is a useful alternative to the lateral microsurgical preauricular approach in carefully selected cases. The vaginal process of the tympanic part of the temporal bone provides a valuable landmark to aid in accessing the jugular foramen in both procedures and can be drilled to open the foramen in the preauricular approach.

Facial-zygomatic triangle: a relationship between the extracranial portion of facial nerve and the zygomatic arch.

BACKGROUND: This study was conducted to clarify the relationships between the extracranial portion of the facial nerve (EFN) and the zygomatic arch (ZA). METHOD: Four cadaveric heads (8 parotid regions), examined under 3-40x magnification, were dissected from lateral to medial to expose the EFN. FINDINGS: In a vertical plane just anterior to the tragus, the distance from the superior edge of the ZA to the facial nerve (FN) is, on average, 26.88 mm. The FN then courses superiorly and anteriorly, crossing the ZA 18.65 mm anterior to the tragus on average. Thus, three points can be used to depict a triangle: A, at the level of the anterior border of the tragus, just above the superior edge of the ZA; B, 26 mm below A; and C, 18 mm anterior to A. This so called facial-zygomatic triangle represents the area where surgical dissection can be performed with no risk of damaging the FN. Thus, the closer one stays to the tragus, the lesser the risk of damaging the FN below the ZA. If the incision is carried out on a vertical plane closer to the tragus, the skin can be safely cut up to 2 cm below the ZA. CONCLUSION: The facial-zygomatic triangle is a very useful superficial landmark to avoid FN damage when working below the ZA.

Middle meningeal origin of the ophthalmic artery.

OBJECTIVE: To examine the microsurgical anatomy and clinical significance of an anomalous origin of the ophthalmic artery from the middle meningeal artery. METHODS: In the course of an anatomic study of the cavernous sinus, an anomalous ophthalmic artery arising from the middle meningeal artery was found. To further define the anatomy of the region, five additional skulls, in which the arteries and veins were injected with colored latex, were dissected using 3x to 40x magnification. RESULTS: The anomalous ophthalmic artery arose from the frontal branch of the middle meningeal artery, passed through the superior orbital fissure, and supplied the entire contents of the orbit, as well as giving rise to the central retinal artery. This study provides the first display of this anomaly in an anatomic dissection. CONCLUSION: The ophthalmic artery may infrequently arise from the middle meningeal artery. This anomaly places the ophthalmic artery at risk during procedures in which the dura is elevated from the greater and lesser wings of the sphenoid or when the sphenoid ridge is removed and during embolization procedures involving the branches of the external carotid artery.

The architecture of the arcuate eminence-a microanatomical study and its application to the transpetrosal approach.

This study was performed to determine if the arcuate eminence can be drilled down without opening the semicircular canal to obtain a flatter operative field during an anterior or posterior transpetrosal approach. The depth of the superior semicircular canal from the top of the arcuate eminence was measured in 43 dry temporal bones. We found that the arcuate eminence was situated approximately 20 mm from the petrosigmoid intersection, and the superior semicircular canal was located 2.0 mm deep from the top of the arcuate eminence (range, 0.2 mm to 4.2 mm). The arcuate eminence consists of either (1) the otic capsule and additional overlying bone, (2) the naked otic capsule of normal thickness, or (3) the thinned otic capsule. In cases strictly selected by preoperative computed tomography, it may be possible to drill down the arcuate eminence with meticulous manipulation. The relationship between opening the semicircular canal and hearing preservation is also discussed.

Persistent trigeminal artery: a unique anatomic specimen--analysis and therapeutic implications.

OBJECTIVE: Persistent primitive carotid-basilar artery anastomoses are uncommon, and are usually seen on an angiogram or discovered at autopsy. The most frequent type of anastomosis is the persistent trigeminal artery. METHODS: A single case of a medial variation of the persistent trigeminal artery, as seen in a well-preserved human adult anatomic specimen injected with red latex, is presented, and the anatomy of this uncommon anastomosis is discussed. RESULTS: This specimen is unique in its clear preservation of the artery, which arises from the medial portion of the right intracavernous carotid artery and gives rise to two branches, the inferior hypophyseal artery and the dorsal meningeal artery to the clivus. CONCLUSION: A new variation of the persistent trigeminal artery is described, which is important to support the possibility that more than one variety of carotid-basilar anastomosis exists in this region.

Unilateral upper and lower subtotal maxillectomy approaches to the cranial base: microsurgical anatomy.

OBJECTIVE: The relationship of the maxilla, with its thin walls, to the nasal and oral cavities, the orbit, and the infratemporal and pterygopalatine fossae makes it a suitable route for accessing lesions involving both the central and lateral cranial base. In this study, we compared the surgical anatomy and exposure obtained by two unilateral transmaxillary approaches, one directed through an upper subtotal maxillectomy, and the other through a lower subtotal maxillectomy. METHODS: Cadaveric specimens examined, with 3 to 40x magnification, provided the material for this study. RESULTS: Both upper and lower maxillectomy approaches open a surgical field extending from the ipsilateral internal carotid artery to the contralateral Eustachian tube; however, they differ in the direction of the access and the areas exposed. The lower maxillectomy opens a combination of the transmaxillary, transnasal, and transoral routes to extra- and intradural lesions of the central cranial base. Performing additional osteotomies of the mandibular coronoid process and the sphenoid pterygoid process provides anterolateral access to the lateral cranial base, including the pterygopalatine and infratemporal fossae, and the parapharyngeal space. The upper maxillectomy opens the transmaxillary and transnasal routes to the central cranial base but not the transoral route. The structures exposed in the lateral cranial base, after removing the coronoid and pterygoid processes, include the pterygopalatine and infratemporal fossae and the parapharyngeal space. Exposure can be extended by a frontotemporal craniotomy, which provides access to the anterior and middle cranial fossae and the basal cisterns. CONCLUSION: The upper and lower subtotal maxillectomy approaches provide wide but differing access to large parts of the central and lateral cranial base depending on the site of the osteotomies.

Trajectory of the hypoglossal nerve in the hypoglossal canal: significance for the transcondylar approach.

A microanatomical study of the hypoglossal canal and its surrounding area was carried out using dry skulls and cadaveric heads to determine the course of the hypoglossal nerve in the hypoglossal canal, especially the significance for the transcondylar approach. The hypoglossal nerve enters the superomedial part of the hypoglossal canal as two bundles, which then change course abruptly to an anterosuperior direction, and unite as one trunk before exiting the canal. The hypoglossal nerve has an oblique course in the canal rather than being located in the center, and exits through the inferolateral part of the canal. A venous plexus surrounds the entire length of the nerve bundles in the canal. The present results suggest that during drilling the occipital condyle toward the hypoglossal canal from behind, the surgeon does not need to be overly concerned even if some bleeding occurs from the posterolateral edge of the hypoglossal canal.

Telovelar approach to the fourth ventricle: microsurgical anatomy.

OBJECT: In the past, access to the fourth ventricle was obtained by splitting the vermis or removing part of the cerebellum. The purpose of this study was to examine the access to the fourth ventricle achieved by opening the tela choroidea and inferior medullary velum, the two thin sheets of tissue that form the lower half of the roof of the fourth ventricle, without incising or removing part of the cerebellum. METHODS: Fifty formalin-fixed specimens, in which the arteries were perfused with red silicone and the veins with blue silicone, provided the material for this study. The dissections were performed in a stepwise manner to simulate the exposure that can be obtained by retracting the cerebellar tonsils and opening the tela choroidea and inferior medullary velum. CONCLUSIONS: Gently displacing the tonsils laterally exposes both the tela choroidea and the inferior medullary velum. Opening the tela provides access to the floor and body of the ventricle from the aqueduct to the obex. The additional opening of the velum provides access to the superior half of the roof of the ventricle, the fastigium, and the superolateral recess. Elevating the tonsillar surface away from the posterolateral medulla exposes the tela, which covers the lateral recess, and opening this tela exposes the structure forming the walls of the lateral recess.

The pretemporal transcavernous approach to the interpeduncular and prepontine cisterns: microsurgical anatomy and technique application.

OBJECTIVE: To illustrate in a stepwise fashion the microsurgical anatomy of the transcavernous approach to the interpeduncular and prepontine cisterns and to discuss our initial results with 15 basilar tip aneurysms managed through that approach. METHODS: Using 10 embalmed cadaveric heads perfused with colored silicon, we performed bilateral stepwise dissections of the transcavernous approach via an orbitozygomatic pretemporal craniotomy. Measurements of the exposure of the basilar artery obtained along the dorsum sellae and upper clivus were taken. Our clinical data were derived from a series of 15 patients with large basilar tip aneurysms treated surgically via the transcavernous approach between 1997 and 1999. Indications for surgery were based on the size of the aneurysm (all were large) and its position in relation to the dorsum sellae (eight were more than 5 mm below the level of the dorsum sellae). RESULTS: Good exposure of the neurovascular structures of the interpeduncular and prepontine cisterns (namely, the basilar artery) was obtained in all cases as compared with other well-established approaches to the area. All patients in our surgical series did well except that all incurred an expected third nerve palsy, caused by surgical manipulation, which resolved over the course of 2 weeks to 3 months. CONCLUSION: Although technically difficult, the transcavernous approach provides better exposure of the interpeduncular and prepontine cisterns relative to that afforded by other, more conventional approaches. The satisfactory results obtained in our preliminary series of patients greatly support the use of this approach for complex basilar tip aneurysms.

[Infratemporal fossa approach for mid-skull base lesion: its usefulness, surgical anatomy, and intraoperative device].

The usefulness of the infratemporal fossa type C approach is reported through a presentation of a case of clival chordoma, which was successfully treated by this approach. Although it is complicated and includes some demerits, this approach gives a shorter and wider access to mid-skull base pathology than other approaches. Among the demerits, deformity of the temporal region caused by extensive drilling of the bone could be minimized by cosmetic mastoidectomy, which was first applied during this approach by the authors. The surgical anatomy for this approach is demonstrated using a cadaver specimen.