The Posterior Fossa Microsurgical Anatomy and Approaches.pdf

FOREWORD

prove the care of my patients. It represents a lifelong

attempt to gain an understanding of the anatomy and

intricacies of the brain that would improve the safety, gentle-

ness, and accuracy of surgery for my patients. During college,

I planned to pursue a career in social work but, during a

course on psychology and the brain, I became captivated by

the possibility of serving humanity through a career in neu-

rosurgery. During medical school, I began working in a neu-

roscience laboratory in my spare time and, at the end of my

residency, I completed a fellowship in neuroanatomy. It was

during this fellowship that I realized the potential for greater

knowledge about microneurosurgical anatomy to improve

the care of my patients. This volume, a distillation of our

studies of the posterior fossa, represents nearly 40 years of

work and study in which more than 50 residents and fellows

have participated, resulting in several hundred publications.

It has been gratifying to view the role of our fellows and

trainees in spreading this knowledge to other countries and

around the world and to see the benefits of neurosurgeons

applying this knowledge to improve surgery for their patients

( Table 1 ). Especially gratifying has been the association with Drs.

Katsutoshi Kitamura, Masashi Fukui, and Toshio Matsushima in

Fukuoka, Japan, and Drs. Evandro de Oliveira, Helder Tedeschi,

and Hung Wen in S˜ o Paulo, Brazil. It is to the fellows and

associates in the microsurgery laboratory that this volume is

dedicated. Special thanks go to our medical illustrators, David

Peace and Robin Barry, who have worked with us for 2

decades; to Ron Smith, who has directed the microsurgery

laboratory for many years; and to Laura Dickinson and Fran

Johnson, who have labored over these and earlier manuscripts.

In the beginning, nearly 40 years ago, even with microsur-

gical techniques, our dissections were crude by current stan-

dards, with photographs needing to be retouched to bring out

the facets of anatomy important in achieving a satisfactory

outcome at surgery. Over the years, as we have learned to

expose fine neural structures, the display of microsurgical

anatomy has become more vividly accurate and beautiful

than we had imagined at the onset, and it has enhanced the

accuracy and beauty of our surgery. We hope that it will do

the same for our readers. We plan to produce a second issue

on the cerebrum and supratentorial areas in 2002 for the 25th

anniversary of Neurosurgery , which I had some role in birth-

ing, as President of the Congress of Neurological Surgeons 22

years ago.

In the early development of neurosurgery, approaches to

the posterior fossa were directed largely via the occipital

squama and less frequently via the subtemporal transtentorial

route. With the development of microsurgery and cranial base

TABLE 1. Residents and Fellows Who Have Worked in Dr.

Rhoton’s Microsurgery Laboratory

Name

Location

Hajime Arai

Tokyo, Japan

Allen S. Boyd, Jr.

Memphis, Tennessee

Christopher C. Carver

Salinas, California

Evandro de Oliveira

S˜o Paulo, Brazil

W. Frank Emmons

Olympia, Washington

J. Paul Ferguson

Rome, Georgia

Andrew D. Fine

Gainesville, Florida

Brandon Fradd

Gainesville, Florida

Kiyotaka Fujii

Fukuoka, Japan

Hirohiko Gibo

Nagano, Japan

John L. Grant

Portsmouth, Virginia

Kristinn Gudmundsson

Reykjavik, Iceland

David G. Hardy

Cambridge, England

Frank S. Harris

Temple, Texas

Tsutomo Hitotsumatsu

Fukuoka, Japan

Takuya Inoue

Fukuoka, Japan

Tooru Inoue

Fukuoka, Japan

Chang Jin Kim

Seoul, South Korea

Toshiro Katsuta

Fukuoka, Japan

Shigeaki Kobayashi

Matsumoto, Japan

William Lineaweaver

Stanford, California

J. Richard Lister

Peoria, Illinois

Qing Liang Liu

Beijing, China

Jack E. Maniscalco

Tampa, Florida

Richard G. Martin

Huntsville, Alabama

Haruo Matsuno

Fukuoka, Japan

Toshio Matsushima

Fukuoka, Japan

J. Robert Mozingo

(Deceased)

Hiroshi Muratani

Fukuoka, Japan

Antonio C. M. Mussi

S˜o Paulo, Brazil

Shinji Nagata

Fukuoka, Japan

Yoshihiro Natori

Fukuoka, Japan

Kazunari Oka

Fukuoka, Japan

Michio Ono

Tokyo, Japan

T. Glenn Pait

Little Rock, Arkansas

Wayne S. Paullus

Amarillo, Texas

David Perlmutter

Sarasota, Florida

Wade H. Renn

Valdosta, Georgia

Saran S. Rosner

Hawthorne, New York

Naokatsu Saeki

Chiba, Japan

Shuji Sakata

Fukuoka, Japan

Eduardo Seoane

Buenos Aires, Argentina

Xiang-en Shi

Beijing, China

Ryusui Tanaka

Tokyo, Japan

Helder Tedeschi

S˜o Paulo, Brazil

Erdener Timurkaynak

Ankara, Turkey

Hung T. Wen

S˜o Paulo, Brazil

C. J. Whang

Seoul, South Korea

Isao Yamamoto

Yokohama, Japan

Arnold A. Zeal

Jacksonville, Florida

Neurosurgery, Vol. 47, No. 3, September 2000 Supplement

The Posterior Cranial Fossa: Microsurgical Anatomy

and Surgical Approaches

T his work has grown out of my personal desire to im-

Robert Buza

Salem, Oregon

S6 Rhoton

surgery, it became possible to work in long, narrow expo-

sures, thus setting the stage for opening virtually all of the

cranial base through carefully placed windows exposing

small and selective parts of the posterior fossa. These devel-

opments led to approaches to the posterior fossa via the

temporal bone as well as set the stage for approaches directed

via the anterior and middle cranial base. In this volume, we

have attempted not only to display the brain and cranial base

in the best views for understanding the anatomy, but also to

show the anatomy as exposed in opening multiple surgical

routes to the posterior fossa. For those wanting even greater

detail than displayed in this volume, our prior works, pub-

lished largely in Neurosurgery and the Journal of Neurosurgery ,

can be consulted.

This work has been sustained by numerous private contri-

butions to our department and the University of Florida. Most

prominent among these has been the R.D. Keene family, who

made the first $1 million gift to the University of Florida, a gift

that has supported our work for many years. Their gift was

followed by additional endowments, totaling $16 million,

which support many aspects of education and research in

neurosurgery at the University of Florida. These gifts have

endowed the following chairs and professorships: the R.D.

Keene Family Chair, the C.M. and K.E. Overstreet Chair, the

Mark Overstreet Chair, the Albert E. and Birdie W. Einstein

Chair, the James and Newton Eblen Chair, the Dunspaugh-

Dalton Chair, the Edward Shed Wells Chair, the Robert Z. and

Nancy J. Greene Chair, the L.D. Hupp Chair, the William

Merz Professorship, and the Albert L. Rhoton, Jr. Chairman’s

Professorship. The most recent of these is the $4 million gift

establishing the Albert L. Rhoton, Jr. Neurosurgery Professor-

ship, held by William A. Friedman, who has followed me as

Chairman of Neurosurgery. The efforts of the numerous cli-

nicians and scientists recruited, as a result of the Endowed

Chairs, contributed greatly to the founding of the University

of Florida Brain Institute, where our studies of microsurgical

anatomy are being completed. With this volume, we join our

donors in their aspiration to improve the lives of those un-

dergoing brain surgery throughout the world.

Albert L. Rhoton, Jr.

Gainesville, Florida

Cranial cavity drawing by Leonardo da Vinci captures the growing sense of a science of proporations for Renaissance

artists. In addition to serving as anatomical specimens, his drawings remain consummate examples of draftsmanship.

Courtesy, Dr. Edwin Todd, Pasadena, California. (Also see pages S193 and S286.)

Neurosurgery, Vol. 47, No. 3, September 2000 Supplement

CHAPTER 1

Cerebellum and Fourth Ventricle

Albert L. Rhoton, Jr., M.D.

Department of Neurological Surgery, University of Florida, Gainesville, Florida

Key words: Cerebellar artery, Cranial nerve, Fourth ventricle, Intracranial vein, Microsurgical anatomy

three cranial fossae, contains the most complex intracra-

nial anatomy. Here, in approximately one-eighth the

intracranial space, are found the pathways regulating con-

sciousness, vital autonomic functions, and motor activities

and sensory reception for the head, body, and extremities, in

addition to the centers for controlling balance and gait. Only

2 of the 12 pairs of cranial nerves are located entirely outside

the posterior fossa; the 10 other pairs have a segment within

the posterior fossa (22, 25) ( Fig. 1.1 ). The posterior fossa is

strategically situated at the outlet of the cerebrospinal fluid

flow from the ventricular system. The arterial relationships

are especially complex, with the vertebral and basilar arteries

having relatively inaccessible segments deep in front of the

brainstem and the major cerebellar arteries coursing in rela-

tion to multiple sets of cranial nerves before reaching the

cerebellum (9, 10, 18, 19).

The posterior fossa extends from the tentorial incisura,

through which it communicates with the supratentorial space,

to the foramen magnum, through which it communicates

with the spinal canal. It is surrounded by the occipital, tem-

poral, parietal, and sphenoid bones ( Fig. 1.1 ). It is bounded in

front by the dorsum sellae, the posterior part of the sphenoid

body, and the clival part of the occipital bone; behind by the

lower portion of the squamosal part of the occipital bone; and

on each side by the petrous and mastoid parts of the temporal

bone, the lateral part of the occipital bone, and above and

behind by a small part of the mastoid angle of the parietal

bone. Its intracranial surface is penetrated by the jugular

foramen, internal acoustic meatus, hypoglossal canal, the ves-

tibular and cochlear aqueducts, and several venous emissary

foramina, all of which will be explored in greater detail. The

upper surface of the cerebellum is separated from the supra-

tentorial space by the tentorium cerebelli. Optimizing an op-

erative approach to the posterior fossa requires an under-

standing of the relationships of the cerebellum, cranial nerves,

brainstem, the cerebellar arteries, veins, and peduncles, and

the complex fissures between the cerebellum and brainstem.

The relationships of the fourth ventricle to the cerebellar

surfaces and the fissures through which the ventricle is ap-

proached surgically are among the most complex in the brain.

This section on the cerebellum and fourth ventricle will begin

at the cerebellar surfaces and progress to the deeper neural

structures.

CEREBELLAR SURFACES

The cortical surfaces are divided on the basis of the struc-

tures they face, or along which they may be exposed, to make

this description more readily applicable to the operative set-

ting ( Fig. 1.2 ). The first surface, the tentorial surface, faces the

tentorium and is retracted in a supracerebellar approach; the

second surface, the suboccipital surface, is located below and

between the lateral and sigmoid sinuses and is exposed in a

suboccipital craniectomy; and the third surface, the petrosal

surface, faces forward toward the posterior surface of the

petrous bone and is retracted to expose the cerebellopontine

angle. Each of the surfaces has the vermis in the midline and

the hemispheres laterally and is divided by a major fissure

named on the basis of the surface that it divides. The hemi-

spheric lobules forming each of the three surfaces commonly

overlap onto and form a part of the adjacent surfaces (22). The

fissures dividing the three cortical surfaces are to be distin-

guished from the fissures between the cerebellum and the

brainstem.

Tentorial surface

The tentorial surface faces and conforms to the lower sur-

face of the tentorium ( Figs. 1.2–1.4 ). The anteromedial part of

this surface, the apex, formed by the anterior vermis, is the

highest point on the cerebellum. This surface slopes down-

ward from its anteromedial to its posterolateral edge. On the

tentorial surface, the transition from the vermis to the hemi-

spheres is smooth and not marked by the deep fissures on the

suboccipital surface between the vermis and hemispheres.

Deep notches, the anterior and posterior cerebellar incisurae,

groove the anterior and posterior edges of the tentorial sur-

face in the midline. The brainstem fits into the anterior cere-

bellar incisura and the falx cerebelli fits into the posterior

incisura ( Fig. 1.2 ).

Neurosurgery, Vol. 47, No. 3, September 2000 Supplement

T he posterior cranial fossa, the largest and deepest of the

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