鼻咽和颅底英文

Louis M. Teresi, MD #{149}Robert B. Lufkin, MD #{149}Fernando Vinuela, MD S Rosiland B. Dietrich, MD #{149}Gabriel H. Wilson, MD #{149}John R. Bentson, MD #{149}William N. Hanafee, MD MR Imaging of the Nasopharynx and Floor 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. MR images from five healthy volunteers were correlated with whole-organ cryomicrotome sections from three cadavers. Anatomic connections ex- ist between the paranasopharyngeal spaces and the surface structures of the skull base. These anatomic con- nections include the intimate rela- tionship between the eustachian tube and the pharyngobasilar fascia, the attachment of the muscles of mastication and deglutition to the skull base, and vascular and nervous structures in the foramina. The in- herent contrast between the soft tis- sues of the nasopharynx and related structures and the bone of the floor of the middle cranial fossa allowed excellent 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 Angeles School 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 Service grant number 1K08 CA 00979-01, awarded by the National Cancer Institute, Department of Health and Human Services. Address reprint requests to L.M.T., Department of Radiology, UCLA Medical Center, BL-428, Los Angeles, CA 90024. c RSNA, 1987 See 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 matched whole-organ sections obtained from three cadavers. 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 a multisection two-dimensional Fourier transform rapid spin-echo (SE) technique with a repetition time (TR) of 500 msec and 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 a section thickness of 5 mm and 7-mm sep- arations from center-to-center section. Other images were similarly acquired with 384 phase-encoding levels and inter- polated to a 512 X 512 display matrix which decreased the pixel size from 0.75 x 0.75 mm to 0.5 X 0.5 mm. Seven simul- taneous sections were obtained in each sequence with a total imaging time of 8.5 mm (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 cryomicrotome freezing 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 to permit identification of arteries and veins. In order to preserve topographic anatomy, the soft tissues to be examined were frozen in situ in respect to their skeletal structures before there had been draining of blood or other fluids from the region of interest. The frozen specimens were 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 were mounted on a bed that weighed approxi- mately 400 pounds (181.8 kg). This heavy weight prevented vibrations and insured an even shaving slice. The microtome knife sectioned the specimens at prede- termined thicknesses varying from 5-50 Mm. When photography was desired, the surface of the specimen was gently rubbed with a warm cloth soaked in eth- ylene glycol to produce a frost-free sur- face. Photographs of representative gross sections 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- Administrator Pencil Administrator Pencil Administrator Line Administrator Line Administrator Line Administrator Line Administrator Line Administrator Line Administrator Line 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 lower airway, 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 the pharyngeal tonsil (adenoids) is nor- mally located submucosally and will never obliterate the deeper tissue planes surrounding the nasopharynx. Deep to the lymphoid tissue are the palatal and phanyngeal muscles (6) (Figs. la, 2d, 2e, 2f). The levator veli palatini muscle, some of whose fibers anise from the short limb of the cartilaginous eustachian tube, onigi- nates from the quadmate area of the petrous bone. The tensor ve!i palatini muscle originates from the scaphoid fossa of the sphenoid bone antemola- teral to the levatom veli palatini mus- cle. The levator veli palatini muscle and the cartilaginous portion of the eustachian tube pass directly to the soft palate through an aperture in the pharyngobasilar 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 as bands 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 the signal intensity in this region in- dude the tensor veli palatini, levator veli 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 the skull to the oropharynx (Figs. la, lb. 2d, 2f, 3a). Its boundaries are defined by the buccopharyngeal fascia. The medial part of the buccopharyngeal fascia 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 covers the deep surface of the panotid gland and pterygoid muscles. These layers are sparse and loosely applied to their respective muscles of origin to accommodate the tremendous move- ment of the pharynx that occurs dun- ing swallowing. The buccopharyn- geal fascia is not visible on computed tomography scans or MR images, but it forms the medial and lateral boundaries of the parapharyngeal space. The paraphanyngeal space ap- pears as a loose network of high-sig- na! fibrofatty tissue and is always symmetric. Within the parapharyn- geal space small branches of the ex- ternal carotid artery, pharyngeal veins, and mandibular nerve are seen as round or linear, medium- to low- intensity structures. The infratemponal fossa lies lateral to the paranasopharyngea! space. It is bounded anteriorly by the posterior wall 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 the fonamina, 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 is surrounded by fat, within which can be seen the mandibular branch of the tngeminal nerve. Postemolateral to the fomamen ovale, the foramen spin- osum provides a pathway for the meningeal artery. Numerous smaller foramina connect small branches of the mandibular segment of the max- il!ary artery and pterygoid plexus of veins 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 which attaches to the base of the skull from the posterior margin of the medial pterygoid plate to the petrous part of the temporal bone immediately in front 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 from the medial ptenygoid plate to the ca- rotid foramen, medial to the tensor pa!atini muscle. From the carotid fo- ramina, the fascia reflects medially over the longus coli and rectus capi- tus muscles. The fascia thus forms an entirely closed and very resistant fi- brotic chamber that is continuous with the fibrous tissue occupying the foramen lacerum. The only aperture is the sinus of Morgagni, for the pas- sage of the eustachian tube and fibers of the levator palatini muscle. Near the skull base the fascia is divided into a gutter that is responsible for the strong attachment of the eusta- chian tubes to the base of the skull directly 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 foramen ovale make up a pathway into the cranium since they are in direct com- munication with the cavernous sinus. The eustachian tube travels from the 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 1 cm 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 cm long, 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 greater wing of the sphenoid bone and the apex of the petrous portion of the temporal bone (Figs. ic, le, 3a). The cartilaginous portion first arches downward and forward across the parapharyngeal space. Before the pharyngeal orifice, it makes another slight curve downward and forward. Only the anterior portion of the can- tilage turns infeniorly from this plane. 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 which lies between the pterygoid process and the maxillary sinus. On axial and sagittal 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 perpendicular plate of the palatine bone. The ptery- gopalatine fossa connects with the nasal fossa through this aperture. The pterygopalatine fossa is in free communication with the inferior or- bital fissure superiorly and the infra- temporal fossa laterally. The foramen rotundum, which appears as a line or ring of negligible signal, lies within the greater wing of the sphenoid bone anterior to the point where the medial pterygoid plate joins the basisphenoid bone (Fig. lc). From here, the second division of the tn- geminal nerve passes through the upper pterygomaxi!lary fossa form- ing the sphenopa!atine ganglion as it courses toward the inferior orbital fissure and infraorbita! groove and canal. These nerves appear as small, round soft-tissue structures inconsis- Administrator Pencil Administrator reply 1 Administrator Pencil Administrator Pencil poloti tube Styloid process nt jugular v mt corotido Longus and rectus 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 buccopharyngeal fascia (dotted lines) outlines the limits of the prestyloid parapharyngeal space. The potential retropharyngeal 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 and are 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 the sphenoid 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). Sympathetic and parasympathetic nerves that course with the internal carotid an- tery are transmitted through the pterygoid canal with the pterygoid artery 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 to enter 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 of high signal that correspond to cranial nerves transmitted through the cay- emnous sinus. The abducens nerve (VI) passes through the areolan cavity of the cavernous sinus, and the ocu- lomotor nerve (III) and trochlear nerve (IV) are found in its lateral wall. The optic nerve (II) lies medial to the cavernous sinus. The t