Louis M. Teresi, MD #{149}Robert B. Lufkin, MD #{149}Fernando Vinuela, MDS Rosiland B. Dietrich, MD #{149}Gabriel H. Wilson, MD

#{149}John R. Bentson, MD #{149}William N. Hanafee, MD

MR Imaging of the Nasopharynx andFloor of the Middle Cranial Fossa

Part I. Normal Anatomy’

811

Head and Neck Radiology

The normal anatomy of the naso-pharynx and floor of the middle cra-nial fossa was analyzed with mag-netic resonance (MR) imaging. MRimages from five healthy volunteerswere correlated with whole-organcryomicrotome sections from threecadavers. Anatomic connections ex-ist between the paranasopharyngealspaces and the surface structures ofthe skull base. These anatomic con-nections include the intimate rela-tionship between the eustachiantube and the pharyngobasilar fascia,the attachment of the muscles ofmastication and deglutition to theskull base, and vascular and nervousstructures in the foramina. The in-herent contrast between the soft tis-sues of the nasopharynx and relatedstructures and the bone of the floorof the middle cranial fossa allowedexcellent visualization of these ana-tomic connections.

Index terms: Head, MR studies, 10.1214 #{149}Naso-

pharynx, anatomy, 263.92 #{149}Nasopharynx, MR

studies, 263.1214 #{149}Skull, anatomy, 10.92

Radiology 1987; 164:811-816

1 From the Department of Radiological Sci-ences, University of California Los AngelesSchool of Medicine, Los Angeles (L.M.T.,R.B.L., F.V., R.B.D., G.H.W., J.R.B., W.N.H.).From the 1986 RSNA annual meeting. Received

November 18, 1986; revision requested Febru-ary 10, 1987; revision received April 14; accept-

ed May 6. Supported by Public Health Servicegrant number 1K08 CA 00979-01, awarded bythe National Cancer Institute, Department of

Health and Human Services. Address reprintrequests to L.M.T., Department of Radiology,UCLA Medical Center, BL-428, Los Angeles,CA 90024.

c RSNA, 1987See also the articles by Teresi (pp. 817-821)

and Som (pp. 825-832) in this issue.

W HENEVER a new imaging tech-

nique is applied to a region of

the body it is imperative to first de-

termine what anatomic structures can

be consistently visualized and what

their normal appearance is. The val-

ue of magnetic resonance (MR) in the

evaluation of parts of the skull base

has been described (i-4). The floor of

the middle cranial fossa is frequently

involved in pathologic conditions of

the nasopharynx and related spaces;

the anatomy is complex. This study

was undertaken to delineate the nor-

mal anatomy of the nasopharynx and

floor of the middle cranial fossa as

seen on MR images by correlating

MR images of healthy volunteers

with whole-organ cryomicrotome

sections from cadavers. Special atten-

tion was given to anatomic structures

connecting the nasopharynx and me-

lated spaces with the middle cranial

fossa.

MATERIALS AND METHODS

MR images from five healthy volun-teers were compared with matchedwhole-organ sections obtained from threecadavers. MR examinations of the naso-

pharynges of healthy volunteers were

performed with a 0.3-T permanent-mag-

net imaging system (Fonar B-3000; Fonar,

Melville, N.Y.) with the use of either a so-lenoid surface or a 24-cm bore head re-

ceiver coil. Images were acquired using amultisection two-dimensional Fourier

transform rapid spin-echo (SE) technique

with a repetition time (TR) of 500 msecand an echo time (TE) of 28 msec (SE 500/28). Four excitations in a 256 X 256 matrix

for each image usually were used with asection thickness of 5 mm and 7-mm sep-arations from center-to-center section.Other images were similarly acquiredwith 384 phase-encoding levels and inter-polated to a 512 X 512 display matrix

which decreased the pixel size from 0.75x 0.75 mm to 0.5 X 0.5 mm. Seven simul-

taneous sections were obtained in eachsequence with a total imaging time of 8.5mm (256 X 256 matrix) or 12.8 mm (512 X

512 matrix). Images were obtained in

axial, coronal, and sagittal planes.Whole-organ sections from the cadav-

ers were prepared using a cryomicrotomefreezing and sectioning technique de-scribed by Rauschning et al. (5). The spec-imens were first prepared with an injec-

tion of a pigmented barium compound topermit identification of arteries andveins. In order to preserve topographic

anatomy, the soft tissues to be examinedwere frozen in situ in respect to theirskeletal structures before there had beendraining of blood or other fluids from theregion of interest. The frozen specimenswere transferred to a horizontal section-ing, heavy-duty sledge cryomicrotome

(LKB 2250; Broma Co.; Stockholm, Swe-den). Inside the freezing compartment of

the cryomicrotome, the specimens weremounted on a bed that weighed approxi-

mately 400 pounds (181.8 kg). This heavyweight prevented vibrations and insuredan even shaving slice. The microtomeknife sectioned the specimens at prede-termined thicknesses varying from 5-50

Mm. When photography was desired, thesurface of the specimen was gentlyrubbed with a warm cloth soaked in eth-ylene glycol to produce a frost-free sur-

face. Photographs of representative grosssections were then compared with the re-

spective MR images from the healthy vol-unteers.

RESULTS

MR Images of Normal Anatomy

The nasopharynx is an inverted J-shaped muscular sling suspended

from the floor of the middle cranial

fossa. Involved in both deglutition

and respiration, the nasopharynx

connects with the nasal cavity anteni-

only and with the omopharyngeal cay-

ity infeniorly. It is bounded superior-

ly by the floor of the sphenoid bone

and the clivus, posteriorly by the pre-

vertebral musculature of C-i and C-2,

and laterally by the pamapharyngeal

constrictor muscles and deep soft tis-

sues of the panapharyngeal space and

infratemporal fossa.

Superficial soft tissues-At upper

levels of the nasopharynx, the bilat-

b. c.

e.

Figure 1. Serial axial (SE 500/28) MR images and matched whole-organ cryosections from lowest level (a) to highest level (c). (a) Level of

the eustachian tube orifice. (b) and (d) Level of the high nasopharynx. (c) and (e) Level of the sphenopalatine foramen and pterygoid canal.

Refer to key for definitions of abbreviations.

Key for Figures

C clivus Iji levator palatini muscle Pf pterygopalatine fossa

Ca carotid artery lpp lateral pterygoid plate PG parotid gland

CC carotid canal it lymphoid tissue �n’ pterygoid veins

cFL cartilaginous base of foramen lacerum M maxillary sinus pvc pterygo-vaginal canal

Cs cavernous sinus Ma mandible RC rectus capitus muscle

fT eustachian tube i�za maxillary artery branches S sphenoid sinus

t’fO eustachian tube orifice MC Meckel cavity Sf sphenopalatine foramen

FL foramen lacerum ME middle ear Srnf sphenomaxillary fissure

FO foramen ovale Mf middle cranial fossa SOf superior orbital fissure

FR foramen rotundum ninia middle meningeal artery SP soft palate

fR fossa of Rosenmueller MP medial pterygoid muscle ST sulcus tubae auditivae

fS foramen spinosum nip medial ptervgoid plate T temporalis muscle

GW greater wing of sphenoid Ms masseter muscle TG trigeminal ganglion

HP hard palate on orbital apex tp tensor palatini muscle

lot inferior orbital fissure �,l optic nerve TT torus tubarius

IT inferior turbinate P pterygoid process V trigeminal nerve

JF jugular foramen �a palatine artery Vi ophthalmic nerve

Iv jugular vein PA petrous apex V2 maxillary nerve

LC longus coli muscle phf pharyngobasilar fascia V.3 mandibular nerve

LP lateral pterygoid muscle Pc ptervgoid canal

812 #{149}Radiology September 1987

b. c.

Volume 164 Number 3 Radiology #{149}813

e.

g.

Figure 2. Serial coronal (SE 500/28) MR images and matched whole-organ cryosections from most anterior level (a) to more posterior level

(g). (a) and (b) Level of the sphenopalatine foramen. (c) Level of pterygopalatine fossa and anterior pterygoid process. (d) and (e) Level of

foramen ovale. (f) and (g) Level of foramen lacerum. Refer to key for definitions of abbreviations.

enally paired recesses of the airway

are a characteristic finding (Figs. la,

2c). The orifice of the eustachian tube

is seen just anterior (on axial images)

or inferior (on coronal images) to the

torus tubanius, the most prominent of

the superficial landmarks of the na-

sopharynx. The cartilaginous end of

the eustachian tube is usually of simi-

lam or lower signal intensity than sum-

rounding muscles. If tubular tonsillan

tissue is present, this area may have a

fairly intense signal depending on

the amount of lymphoid tissue pres-

ent and the effects of volume averag-

ing. The lateral pharyngeal recess

(fossa of Rosenmueller) is an air-

filled space which projects posterior

to the torus tubamius and muscular

prominence of the levaton palatini

muscle.

Lymphoid tissue lines the muscu-

lam sling of the nasopharynx and is

most prominent along the roof of the

nasopharynx. The signal of lymphoid

tissue is always more intense than

that of muscle (Fig. la, ib). This

bright strip of lymphoid tissue lines

the roof and walls of the nasophar-

ynx, often filling the fossae of Rosen-

814 #{149}Radiology September 1987

mueller. On axial images of the lowerairway, hypentrophied lymphoid tis-sue may have a lobulated on undulat-ing surface contour. On coronal im-ages it will appear to hang down

from the roof of the nasopharynx(Fig. 2c). The lymphoid tissue of thepharyngeal tonsil (adenoids) is nor-

mally located submucosally and willnever obliterate the deeper tissueplanes surrounding the nasopharynx.

Deep to the lymphoid tissue arethe palatal and phanyngeal muscles(6) (Figs. la, 2d, 2e, 2f). The levator

veli palatini muscle, some of whosefibers anise from the short limb of thecartilaginous eustachian tube, onigi-nates from the quadmate area of thepetrous bone. The tensor ve!i palatinimuscle originates from the scaphoidfossa of the sphenoid bone antemola-teral to the levatom veli palatini mus-cle. The levator veli palatini muscleand the cartilaginous portion of theeustachian tube pass directly to thesoft palate through an aperture in thepharyngobasilar fascia called the si-

nus of Mongagni (6). The tensor veli

palatini muscle reaches the palate in-directly by hooking around the ham-ulus of the medial pterygoid plate.These muscles are routinely visible asbands of intermediate signal intensi-

ty flanking the airway. At the level

of the hand palate, the superior con-stnictor muscle and Passavant muscle

mainly bound the nasopharynx pos-

terolaterally. On axial images, these

muscles appear as a band of intenme-

diate intensity surrounding the later-

al and posterior walls of the airway.Other muscles that contribute to thesignal intensity in this region in-dude the tensor veli palatini, levatorveli palatini, salpingopharyngeus,and palatopharyngeus.

Parapharyngeal space and infratem-

poral fossa.-The panapharyngeal

space lies latenial to the palatal mus-des and extends from the base of theskull to the oropharynx (Figs. la, lb.2d, 2f, 3a). Its boundaries are definedby the buccopharyngeal fascia. The

medial part of the buccopharyngealfascia is the epimysium of the supeni-or phanyngeal constrictor muscle.

The lateral boundary of the bucco-pharyngeal fascia is a reflection of

the deep cervical fascia, which coversthe deep surface of the panotid glandand pterygoid muscles. These layersare sparse and loosely applied totheir respective muscles of origin toaccommodate the tremendous move-ment of the pharynx that occurs dun-ing swallowing. The buccopharyn-geal fascia is not visible on computedtomography scans or MR images, but

it forms the medial and lateralboundaries of the parapharyngealspace. The paraphanyngeal space ap-

pears as a loose network of high-sig-na! fibrofatty tissue and is alwayssymmetric. Within the parapharyn-

geal space small branches of the ex-ternal carotid artery, pharyngealveins, and mandibular nerve are seenas round or linear, medium- to low-intensity structures.

The infratemponal fossa lies lateralto the paranasopharyngea! space. It isbounded anteriorly by the posteriorwall of the maxillary antrum and lat-enally by the deep head of the tem-poralis muscle and the zygomatic

arch. The medial and lateral ptery-goid muscles fill the bulk of the in-fratemponal fossa. Superiorly, numer-ous foramina perforate the base of

the sphenoid bone. The largest of thefonamina, the fonamen ovale, is nou-tine!y visible as a defect in the cortex

of the sphenoid bone and is appmeci-ated best on coronal images (Fig. 2d).The orifice of the fonamen ovale issurrounded by fat, within which can

be seen the mandibular branch of thetngeminal nerve. Postemolateral tothe fomamen ovale, the foramen spin-osum provides a pathway for the

meningeal artery. Numerous smallerforamina connect small branches ofthe mandibular segment of the max-il!ary artery and pterygoid plexus ofveins and are infrequently seen on

MR images.Pharyngobasilar fascia and eustachian

tube.-The configuration of the naso-pharynx is determined by the very

tough pharyngobasilar fascia whichattaches to the base of the skull fromthe posterior margin of the medialpterygoid plate to the petrous part ofthe temporal bone immediately infront of the carotid fomamina (Figs. 1,3). Its fibers are continuous with that

of the foramen lacerum (7) (Fig. lb.ld). On axial and coronal images, the

pharyngobasi!ar fascia is seen as a

low-intensity line extending fromthe medial ptenygoid plate to the ca-rotid foramen, medial to the tensorpa!atini muscle. From the carotid fo-ramina, the fascia reflects mediallyover the longus coli and rectus capi-tus muscles. The fascia thus forms an

entirely closed and very resistant fi-

brotic chamber that is continuouswith the fibrous tissue occupying theforamen lacerum. The only apertureis the sinus of Morgagni, for the pas-

sage of the eustachian tube and fibersof the levator palatini muscle. Nearthe skull base the fascia is dividedinto a gutter that is responsible for

the strong attachment of the eusta-

chian tubes to the base of the skulldirectly between the fonamen Ia-

cerum medially and foramen ovale

laterally. This relationship is best ap-

pmeciated on axial images (Fig. ic).The foramen lacerum and foramenovale make up a pathway into the

cranium since they are in direct com-munication with the cavernous sinus.

The eustachian tube travels fromthe skull base to the nasopharynx as a

slowly curving, invented S. Because

of its S-shaped course, only small

segments of it are seen on axial on

coronal images. The bony part, over 1cm long, tapers down from the ante-nor wall of the middle ear to its on-

fice, which is known as the isthmus.The cartilaginous portion, over 2 cmlong, joins the bony part at the isth-

mus and fits into a sulcus on the skull

base, the sphenoid sulcus (sulcus tu-bae auditivae) between the greaterwing of the sphenoid bone and theapex of the petrous portion of thetemporal bone (Figs. ic, le, 3a). Thecartilaginous portion first arches

downward and forward across theparapharyngeal space. Before thepharyngeal orifice, it makes anotherslight curve downward and forward.Only the anterior portion of the can-tilage turns infeniorly from thisplane. Here the torus tubanius rests

against and fits into a small depres-

sion on the posterior margin of the

media! pterygoid plate.Pterygopalatine fossa.-The pterygo-

palatine fossa is a medial depression

of the pterygomaxillary fissure whichlies between the pterygoid process

and the maxillary sinus. On axial andsagittal images it appears as a flat

space filled with high-signal fat(Figs. lc, 2a). The sphenopalatine fo-namen is located at the medial mar-gin of the signal-void perpendicularplate of the palatine bone. The ptery-gopalatine fossa connects with thenasal fossa through this aperture.

The pterygopalatine fossa is in freecommunication with the inferior or-bital fissure superiorly and the infra-

temporal fossa laterally. The foramenrotundum, which appears as a line or

ring of negligible signal, lies within

the greater wing of the sphenoidbone anterior to the point where

the medial pterygoid plate joins thebasisphenoid bone (Fig. lc). Fromhere, the second division of the tn-geminal nerve passes through theupper pterygomaxi!lary fossa form-ing the sphenopa!atine ganglion as itcourses toward the inferior orbitalfissure and infraorbita! groove andcanal. These nerves appear as small,round soft-tissue structures inconsis-

poloti

tube

Styloid process

nt jugular v

mt corotido

Longus andrectus capitus mm

Figure 3. (a) Photograph of normal skull base showing bone landmarks and foramina and

the insertion of the pharyngobasilar fascia (broken line). (b) Composite axial diagram of the

nasopharynx. Right half of the diagram is at a level about 1 cm more cephalad than the left

half. The pharyngobasilar fascia (heavy black line) surrounds the airway and encloses the

cartilaginous end of the eustachian tube and levator palatini muscle. The buccopharyngealfascia (dotted lines) outlines the limits of the prestyloid parapharyngeal space. The potentialretropharyngeal space (dashed line) lies between the pharyngobasilar fascia and the prever-

tebral musculature. CC = carotid canal, FL foramen lacerum, FO foramen ovale, fS fo-

ramen spinosum, JF jugular foramen, lpp lateral pterygoid plate, mp medial pterygoid

plate, pbf = pharyngobasilar fascia, Pc pterygoid canal, pvc pterygo-vaginal canal, Sf

sphenopalatine foramen, ST sulcus tubae auditivae.

Volume 164 Number 3 Radiology #{149}815

round low-intensity structures sun-

rounded by high-intensity fat, the in-

dividual branches are rarely seen.Skull base.-The clivus and basisphe-

noid bone make up the posterior wall

and roof of the nasopharynx. Their

cortical margins show no signal andare seen only by virtue of the con-

trast with interfacing higher-signal

soft tissues (Fig. 2). The intimate rela-

tionship of the mucosa, muscles, and

fat lining the clivus and floor of thesphenoid sinus is seen best on con-

onal images. Fatty marrow within the

clivus and sphenoid bone gives a

characteristic high signal. The ptery-goid (vidian) canal can be seen with-

in the basisphenoid bone as a low-signal, rounded (coronal images) on

linear (axial and sagittal images)structure surrounded by high-signal

marrow (Figs. ic, 2c). Sympatheticand parasympathetic nerves that

course with the internal carotid an-

tery are transmitted through thepterygoid canal with the pterygoidartery to the pterygopalatine and na-

sal fossae.The fomamen lacerum forms a gap

between the anterior tip of the pe-tnous apex and the basisphenoid

bone (upper clivus). This gap is in me-ality filled with cartilage, and the ca-

rotid artery does not go through the

cartilage but lies just above the carti-lage as it leaves the carotid canal toenter the posterior cavernous sinus(Fig. 2f). The cartilaginous base of the

foramen lacenum has virtually no sig-

nal, and only a thin strip of fibrofatty

tissue separates it from the signal-

void carotid artery. Above the fora-men lacemum and lateral to the clivus

Cortuloginous .

end of 15 the cavernous sinus.eustochion tube Vascular channels, the carotid an-

tery, and crania! nerves of the cay-ennous sinus can be resolved consis-

tently on MR images (1) (Fig. 2d).

Coronal images show small foci ofhigh signal that correspond to cranial

nerves transmitted through the cay-

emnous sinus. The abducens nerve(VI) passes through the areolan cavityof the cavernous sinus, and the ocu-lomotor nerve (III) and trochlearnerve (IV) are found in its lateralwall. The optic nerve (II) lies medialto the cavernous sinus. The tnigemi-

nal nerve (V) ganglion and its

branches, within Meckel cavity and

the cavernous sinus, are easily seenon good-quality MR images and havean intermediate signal.

tently seen on MR images. Within gives offbranches to the middle cra- CONCLUSIONthe pterygopalatine fossa, the ptery- ma! and infratempomal fossae, orbit,gopalatine segment of the maxillary nose, palate, and pharynx. Although The skull base, nasopharynx, andartery makes a characteristic loop and segments of the artery are seen as related spaces are crossover areas be-

816 #{149}Radiology September 1987

tween the intra- and extracranial

structures of the head and neck.

Their anatomy is detailed and pre-

sents a formidable task in MR imag-

ing (8-12). Herein we have analyzed

the normal MR anatomy of the naso-

pharynx and floor of the middle cra-

nial fossa by correlating MR images

from healthy volunteers with whole-

organ cryomicmotome sections from

cadavers. Anatomic structures con-

necting the nasopharynx and related

spaces with the middle cranial fossa

have been emphasized. The intimate

relationship of the phamyngobasilan

fascia and eustachian tube to the

skull base has been described in de-

tail. The inherent contrast between

the soft tissue of the nasophamynx

and related spaces and the bone of

the floor of the middle cranial fossa

allows excellent visualization of the

numerous fomamina and fissures of

the skull base connecting the intra-

cranial and extracranial compart-

ments. Coronal and axial images are

most useful in making side-to-side

comparisons of relevant struc-

tunes. U

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