Alvaro Campero

The medial wall of the cavernous sinus: microsurgical anatomy.

OBJECTIVE:This study was conducted to clarify the boundaries, relationships, and components of the medial wall of the cavernous sinus (CS). METHODS:Forty CSs, examined under ×3 to ×40 magnification, were dissected from lateral to medial in a stepwise fashion to expose the medial wall. Four CSs were dissected starting from the midline to lateral. RESULTS:The medial wall of the CS has two parts: sellar and sphenoidal. The sellar part is a thin sheet that separates the pituitary fossa from the venous spaces in the CS. This part, although thin, provided a barrier without perforations or defects in all cadaveric specimens studied. The sphenoidal part is formed by the dura lining the carotid sulcus on the body of the sphenoid bone. In all of the cadaveric specimens, the medial wall seemed to be formed by a single layer of dura that could not be separated easily into two layers as could the lateral wall. The intracavernous carotid was determined to be in direct contact with the pituitary gland, being separated from it by only the thin sellar part of the medial wall in 52.5% of cases. In 39 of 40 CSs, the venous plexus and spaces in the CS extended into the narrow space between the intracavernous carotid and the dura lining the carotid sulcus, which forms the sphenoidal part of the medial wall. The lateral surface of the pituitary gland was divided axially into superior, middle and inferior thirds. The intracavernous carotid coursed lateral to some part of all the superior, middle, and inferior thirds in 27.5% of the CSs, along the inferior and middle thirds in 32.5%, along only the inferior third in 35%, and below the level of the gland and sellar floor in 5%. In 18 of the 40 CSs, the pituitary gland displaced the sellar part of the medial wall laterally and rested against the intracavernous carotid, and in 6 there was a tongue-like lateral protrusion of the gland that extended around a portion of the wall of the intracavernous carotid. No defects were observed in the sellar part of the medial wall, even in the presence of these protrusions. CONCLUSION:The CS has an identifiable medial wall that separates the CS from the sella and capsule of the pituitary gland. The medial wall has two segments, sellar and sphenoidal, and is formed by just one layer of dura that cannot be separated into two layers as can the lateral wall of the CS. In this study, the relationships between the medial wall and adjacent structures demonstrated a marked variability.

MICROSURGICAL APPROACHES TO THE PERIMESENCEPHALIC CISTERNS AND RELATED SEGMENTS OF THE POSTERIOR CEREBRAL ARTERY: COMPARISON USING A NOVEL APPLICATION OF IMAGE GUIDANCE

OBJECTIVE:To describe the exposure obtained through six approaches to the perimesencephalic cisterns with an emphasis on exposure of the posterior cerebral artery and its branches. METHODS:Dissections in 12 hemispheres exposed the crural, ambient, and quadrigeminal cisterns and related segments of the posterior cerebral artery. A Stealth Image Guidance workstation (Medtronic Surgical Navigation Technologies, Louisville, CO) was used to compare the approaches. RESULTS:The transsylvian approach exposed the interpeduncular and crural cisterns. The subtemporal approach exposed the interpeduncular and crural cisterns as well as the lower half of the ambient cistern. Temporal lobe retraction and the position of the vein of Labbé limited exposure of the quadrigeminal cistern. Occipital transtentorial and infratentorial supracerebellar approaches exposed the quadrigeminal and lower two-thirds of the ambient cistern. Transchoroidal approaches exposed the posterior third of the crural cistern, the upper two-thirds of the ambient cistern, and the proximal quadrigeminal cistern. Transchoroidal approaches exposed the posterior portion of the P2 segment (P2p) in 9 of 10 hemispheres and were the only approaches that exposed the lateral posterior choroidal arteries and the plexal segment of the anterior choroidal artery. Occipital transtentorial and infratentorial supracerebellar approaches provided access to the P3 segment in all cases and exposed the P2p segment in 4 of 10 hemispheres. The subtemporal approach provided access to the cisternal and crural segments of the anterior choroidal and medial posterior choroidal arteries and exposed the P2p segment in 3 of 10 hemispheres. CONCLUSION:Surgical approaches to lesions of the perimesencephalic cisterns must be tailored to the site of the pathological findings. The most challenging area to expose is the upper half of the ambient cistern, particularly the P2p segment of the posterior cerebral artery.

Microsurgical anatomy of the dural arteries.

OBJECTIVE: The objective was to examine the microsurgical anatomy basic to the microsurgical and endovascular management of lesions involving the dural arteries. METHODS: Adult cadaveric heads and skulls were examined using the magnification provided by the surgical microscope to define the origin, course, and distribution of the individual dural arteries. RESULTS: The pattern of arterial supply of the dura covering the cranial base is more complex than over the cerebral convexity. The internal carotid system supplies the midline dura of the anterior and middle fossae and the anterior limit of the posterior fossa; the external carotid system supplies the lateral segment of the three cranial fossae; and the vertebrobasilar system supplies the midline structures of the posterior fossa and the area of the foramen magnum. Dural territories often have overlapping supply from several sources. Areas supplied from several overlapping sources are the parasellar dura, tentorium, and falx. The tentorium and falx also receive a contribution from the cerebral arteries, making these structures an anastomotic pathway between the dural and parenchymal arteries. A reciprocal relationship, in which the territories of one artery expand if the adjacent arteries are small, is common. CONCLUSION: The carotid and vertebrobasilar arterial systems give rise to multiple branches that supply the dura in a complex and overlapping pattern. A knowledge of the microsurgical anatomy of these dural arteries and their assessment on pretreatment evaluations plays a major role in safe and accurate treatment of multiple lesions.

Microsurgical approaches to the medial temporal region: an anatomical study.

OBJECTIVE: To describe the surgical anatomy of the anterior, middle, and posterior portions of the medial temporal region and to present an anatomic-based classification of the approaches to this area. METHODS: Twenty formalin-fixed, adult cadaveric specimens were studied. Ten brains provided measurements to compare different surgical strategies. Approaches were demonstrated using 10 silicon-injected cadaveric heads. Surgical cases were used to illustrate the results by the different approaches. Transverse lines at the level of the inferior choroidal point and quadrigeminal plate were used to divide the medial temporal region into anterior, middle, and posterior portions. Surgical approaches to the medial temporal region were classified into four groups: superior, lateral, basal, and medial, based on the surface of the lobe through which the approach was directed. The approaches through the medial group were subdivided further into an anterior approach, the transsylvian transcisternal approach, and two posterior approaches, the occipital interhemispheric and supracerebellar transtentorial approaches. RESULTS: The anterior portion of the medial temporal region can be reached through the superior, lateral, and basal surfaces of the lobe and the anterior variant of the approach through the medial surface. The posterior group of approaches directed through the medial surface are useful for lesions located in the posterior portion. The middle part of the medial temporal region is the most challenging area to expose, where the approach must be tailored according to the nature of the lesion and its extension to other medial temporal areas. CONCLUSION: Each approach to medial temporal lesions has technical or functional drawbacks that should be considered when selecting a surgical treatment for a given patient. Dividing the medial temporal region into smaller areas allows for a more precise analysis, not only of the expected anatomic relationships, but also of the possible choices for the safe resection of the lesion. The systematization used here also provides the basis for selection of a combination of approaches.

Microsurgical anatomy of the oculomotor cistern.

OBJECTIVE: To define the characteristics of the arachnoidal sleeve and cistern that accompany the oculomotor nerve through the cavernous sinus roof. METHODS: Forty cavernous sinuses were examined using 3 to 40x magnification. Information was obtained about the size of the oculomotor cistern and its relationship to the roof of the cavernous sinus and anterior clinoid process. RESULTS: An arachnoidal sleeve and cistern, referred to as the oculomotor cistern, accompanied the oculomotor nerve into the roof of all the cavernous sinuses examined. The oculomotor cistern extends from the oculomotor porus, where the nerve enters the roof of the cavernous sinus, to the area below the tip or the adjacent part of the lower margin of the anterior clinoid process. From the porus, the nerve passes forward and downward to the depth of the cistern where it becomes incorporated into the fibrous lateral wall of the cavernous sinus. The width of the cistern was maximal at the oculomotor porus averaged 5.5 mm (range, 3.0–9.2 mm), and tapered slightly towards the midpoint and deep end of the cistern. The cistern’s average length was 6.5 mm (range, 3.0–11.0 mm). The oculomotor nerve usually coursed closer to the anterior than the posterior wall of the cistern at the level of the oculomotor porus. CONCLUSION: The oculomotor cistern, an arachnoidal and dural cuff, accompanies the oculomotor nerve through the cavernous sinus roof to the area just below or anterior to the lower edge of the tip of the anterior clinoid process. The segment of the nerve inside the oculomotor cistern is interposed between its free portion in the interpeduncular cistern and the part of its course where it is incorporated into the fibrous lateral wall of the cavernous sinus. The cistern can be opened to aid in the exposure and mobilization of the nerve in dealing with pathology in the area.

Microsurgical anatomy of the diaphragma sellae and its role in directing the pattern of growth of pituitary adenomas.

OBJECTIVETo evaluate the anatomic aspects of the diaphragma sellae and its potential role in directing the growth of a pituitary adenoma. METHODSTwenty cadaveric heads were dissected and measurements were taken at the level of the diaphragma sellae. RESULTSThe diaphragma sellae is composed of two layers of dura mater. There is a remarkable variation in the morphology of the diaphragm opening. The average anteroposterior distance of the opening was 7.26 mm (range, 3.4–10.7 mm) and the average lateral-to-lateral distance was 7.33 mm (range, 2.8–14.1 mm). CONCLUSIONThe variability in the diameter of the opening of the diaphragma sellae could explain the growth of pituitary tumors toward the cavernous sinus or toward the suprasellar region.

Surgical anatomy of the dural walls of the cavernous sinus.

The external structure of each cavernous sinus (CS) is made of four dural walls. The aim of this study was to describe the anatomy of the dural walls of the CS. We studied 42 adult cadaveric heads, fixed with formalin and injected with coloured silicon. The main findings were: (i) the lateral wall of the CS has two layers - the external, which is thick and pearly grey, and the internal, which is semi-transparent and containing the cranial nerves (CNs); (ii) the medial wall of the CS has two areas - sellar and sphenoidal, both made up of one dural layer only; and (iii) the superior wall of the CS is formed by three triangles - oculomotor, clinoid and carotid - CN III may be found in a cisternal space of the oculomotor triangle; and (iv) the posterior wall of the CS is made up of two dural layers - meningeal dura and periostic dura - and this wall is close to the vertical segment of CN VI.

Microsurgical Anatomy of the Orbit: The Rule of Seven

The orbits are paired structures, located on the anterior part of the face. Morphologically, each orbit is a four sided pyramid with a posterior apex and anterior base. In the orbit, all openings are arranged around the base, apex or between the orbital walls. An anatomical characteristic of the orbit is that structures are arranged in groups of seven: there are seven bones, seven intraorbital muscles and seven nerves in the orbit. Tumors confined within the periorbita in the anterior two thirds of the orbit can often be approached extracranially, but those located in the apical area, and especially those on the medial side of the optic nerve, often require a transcranial approach. Thus, knowledge of orbital osteology is paramount in adequately choosing and performing an orbital approach. Understanding the critical topographical elements in this area helps to classify an orbital lesion and provides for a solid basis in choosing the most adequate intraorbital route for its treatment.

Microsurgical anatomy of the sphenoid ostia.

We aimed to determine the position, number and variability of the sphenoid sinus ostia. A total of 32 dry skulls were examined under x6 magnification. The septum and nasal turbinates were removed to expose the anterior wall of the sphenoid sinus. A caliper was used for measurements. We found 2 ostia per skull, except for one (3%), in which the left ostium was absent. The inferior edges of both ostia were found at the same height in only four skulls (12.5%), and the superior edges of both ostia were found at the same height in only one skull (3%). Thus, in 27 skulls (84%) the lower and upper margins of both ostia were at different levels. The distance from the internal edge of the right ostium to the midline was 2.04mm on average (range: 0.3-5.3mm). The distance from the internal edge of the left ostium to the midline was 2.18mm on average (range: 0.2 to 5.1mm). In most skulls, the sphenoid ostia are located at different heights on each side; also a great variability in the distance from the internal border of the ostia to the midline was found. We found this anatomical knowledge useful when performing a transsphenoidal approach to the sella turcica.

Three-piece orbitozygomatic approach.

OBJECTIVE To describe the technical details of a 3-piece orbitozygomatic approach. INTRODUCTION In a 3-piece orbitozygomatic approach, soft tissue exposure is mostly comparable to the classic frontopterional approach. Osseous resection is a 3-piece operation that consists of first performing anterior and posterior cuts along the zygomatic arch, reflecting it down, attached to the masseter. This is followed by a classic frontotemporosphenoidal craniotomy, and finally, an osteotomy of the orbital rim, roof, and lateral wall of the orbit. RESULTS When compared with its 1- and 2-piece counterparts, 3-piece orbitozygomatic craniotomy, as described here, is a relatively simple operation and is thus advisable when considering an anterior or middle fossa approach. Brain exposure is wide, whereas cerebral retraction is minimal. We recommend avoiding orbit sectioning as deep as the superior orbital fissure. CONCLUSION The modifications described herein show the technical features of the 3-piece orbitozygomatic approach, which provides excellent brain exposure with less retraction and a good cosmetic result.