Surgical 2

Surg Radiol Anat (t990) 12 : 203-208

Radiolog,c Anatomy Journal of Clinical Anatomy

© Springer-Verlag 1990

MR of the paranasal sinuses E Beahm, L Teresi, R Lufkin and W Hanafee Department of Radiological Sciences UCLA School of Medicine, Los Angeles, CA 90024, USA

Summary. The purpose of this project was to examine the anatomy and pathology of the paranasal sinuses as seen by MR imaging. This was accomplished through correlations of MR images of normal volunteers with matched cadaver whole organ cryosections. The information obtained 'by MRI was compared to that of plain films and CT in the detection of a variety of conditions affecting the paranasal sinuses. The majority of the pathological processes could be quite adequately imaged by T1 weighted pulsing sequences. When more tissue specific information was required in some infiltrating malignant lesions, T2 weighting pulsing sequences are quite helpful for tumors that crossed the subarachnoid space into the central nervous system or in characterizing tissues in airless sinuses. Other than the single case of osteoid osteoma where X-ray studies were superior, magnetic resonance provided equal or superior information to the X-ray examinations.

Offprint requests : RB Lufkin

Les sinus paranasaux en r~sonance magn~tique

Key words : MRI - sinuses

R~sum~. Le but de ce travail est d'6tudier l'anatomie normale et pathologique des sinus paranasaux en IRM. Ceci a 6t6 effectu6 en corr61ant les images en IRM de volontaires normaux avec des coupes homologues obtenues par cryosection sur cadavres. L'information ainsi obtenue en I R M a 6t6 compar6e h celle des radiographies standard et des explorations scanographiques r6alis6s sur un 6chantillonnage d'affections des sinus paranasaux. La majorit6 des situations pathologiques a 6t6 correctement mise en 6vidence par les s6quences en T1, alors que des informations tissulaires plus sp6cifiques des 16sions infiltrantes malignes ont justifi6 l'emploi de s6quence en T2. C'est en particulier le cas des tumeurs s'6tendant darts les espaces sous-arachnoidiens, vers le syst6me nerveux central, ou pour ddfinir les tissus dans les sinus priv6s d'air. A l'exception d'un seul cas d'ost6ome ost6oide, off l'6tude radiologique conventionnelle s'est av6rde sup6rieure, l'exploration en IRM fournit des informations 6gates ou sup6rieures ~ celles des autres modalit6s radiologiques.

While plain film radiography and CT scanning continue to be the mainstay for imaging the paranasal s., recent breakthroughs for performing low cost MR examinations make s. msease a logical target for application of this new technology [9], The superior soft tissue contrast resolution and multi planar capabilities of MR appear to o f f e r advantages in this area over x-ray imaging techniques. The purpose of this project was to examine the anatomy and pathology of the paranasal s. as seen by MR imaging. This was accomplished through correlations of MR images of normal volunteers with matched cadaver whole organ cryosections. We also wished to assess the sensitivity of MRI in detecting inflammatory disease, spread of tumor, and complications of these entities in the paranasal s. A p r o s p e c t i v e s t u d y was planned to compare the information obtained by MRI to that of plain films and CT in the detection of a variety of conditions affecting the paranasal s.

Paranasal

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E Beahm et al : MR of the paranasal sinuses

Fig. 1 A-F Normal axial anatomy. Cryosections. AB MR sections; CD CT sections; EF cryosections Anatomie normale. Coupes axiales. AB coupes en IRM; CD coupes en TDM; EF cryosections

Materials and m e t h o d s

MRI studies of the paranasal s. were performed in 5 normal volunteers. Comparison was made with matched whole organ cryosections obtained f r o m three cadavers. Whole organ cryosections were prepared using a cryomicrotome technique described by Rauschning [6]. T h e c a d a v e r s w e r e first prepared by arterial injection of a pigmented barium compound to permit identification of arteries and veins. The air-filled paranasal s. were irrigated and filled with clear or colored saline to improve visualization. The specimens were then frozen intact before there had been drainage of blood or other fluids and cut with a band saw to small blocks for sectioning.

The blocks were then transferred to a horizontal sectioning heavy duty sledge cryomicrotome (LKB 2250, Bromma, Sweden). Inside the cabinet-like freezing compartment, the specimens were mounted on a 400 pound bed. This weight minimized vibrations and ensured an e v e n s h a v i n g s l i c e . T h e m i c r o t o m e knife sectioned the specimens at p r e d e t e r m i n e d thicknesses varying from 5 to 50 microns. At intervals when photography was desired, the cut surface of the specimen was gently rubbed with a warm cloth soaked in ethylene g l y c o l to p r o d u c e a frost=free surface. Photographs of representative cryosections were then compared to MR images of the living individual. MRI studies of the paranasal s. were performed in 68 patients with

Table 1. Patient population

Diagnosis

MR

Benign sinus disease

Inflammatory disease Mucoperiosteal thickening Retention cyst Mucocele Polyposis Tumor Osteoma Inverting papilloma Lipoma Granuloma

23 5 4 8 1 1 3 3

Malignant sinus disease

Epidermal origin Squamous cell carcinoma Basal cell carcinoma Neural crest origin Esthesioneuroblastoma Metastatic disease Total

5 1 2 2 68

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Fig. 2 A-F Normal coronal anatomy. A, B : MR (SE/500/28); C, D : CT and E, F : matched cryosections Anatomie normale. Coupes coronales. A, B coupes en IRM (SE/500/28); C, D coupes en TDM; E, F cryosections comparatives Key for Figs. 1, 2 AE Anterior ethmoid s. F Frontal s. IT Inferior turbinate M Maxillary s. ME Middle ethmoid s. MT Middle turbinate PE Posterior ethmoid s. S

Sphenoid s. VC Vidian canal CI~ pour les figs. 1, 2 AE s. ethmo'idalant6rieur F s. frontal IT comet inf6rieur M s. maxillaire ME s. ethmoidal moyen MT comet moyen PE s. ethmo~datpostdrieur S s. sph6noidat VC canal vidien

a variety of inflammatory conditions as well as benign and malignant tumors (Table 1) 57 of the patients had CT and or plain film studies of the paranasal s. within 14 days of the M R examination. These studies were independently evaluated by three radiologists in a blinded, prospective fashion. Each study was evaluated for the ability to detect and characterize pathology as well as to define its extent in the p a r a n a s a l s. a n d s u r r o u n d i n g tissues. C o m p a r i s o n was m a d e between the imaging evaluations and with clinical examination and surgical findings when available for patients in each group o f inflammatory disease, benign and malignant tumors.

M R imaging was performed on a 0.3 Tesla permanent magnet whole body instrument (Fonar B3 000, Melville, NY) using a standard 24 cm bore head receiver coil. The standard examination consisted of multislice 2D-FT T1 weighted images obtained in coronal (SE/500/ 28) and axial (SE/800/28) planes using an automated sequence. A 2 5 6 x 2 5 6 matrix with a 19.2 cm field of view yielded 0.75 m m square pixels. Sections were 4 mm thick with a 7 m m center to center width. With one excitation, this automated sequence allowed a basic multiplanar, muttislice sinus M R e x a m i n a t i o n to be o b t a i n e d in 12 rain and 20 s. Sagittal and T2 weighted sequences (SE/200/84) in

all three planes were obtained in selected cases to better characterize fluid collections or define disease extent. Gadolinium D T P A was not used in any o f the MR examinations. Results Normal MR anatomy

T h e p a r a n a s a l s. a r e p a i r e d structures (Figs. 1-2). All border the nasal cavity except the frontal s. The lack o f signal from air and cortical bone on M R creates some difficulty in imaging o f the paranasal ss. Fortunately, all ss. are lined with mucoperiostium which produces increased signal, espe-

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E Beahm et al : MR of the paranasal sinuses

Fig. 3 A-D. Chronic sinusitis. The patient is a 19 year old male who presented with a long history of chronic, recurrent sinus infections. A T1 weighted (SE/500/28) images demonstrate a single septum within the inferior portion of the right maxillary s. (arrow). B While there is no suggestion of mucosal disease or retained secretions in this s., mucoperiosteal thickening is clearly shown in the left maxillary s. (arrow head). C Additionally, a few of the middle ethmoid air cells are opacified (arrow heads). The left frontal s. contains some high signal retained secretions (s) Sinusite chroniqne. Le patient est un jeune garqon ~g6 de 19 ans qui prrsente une longue histoire d'infection sinusienne chronique et rdcidivante. A Image en IRM en T1 (SE/500/28) montrant un septum unique clans la pattie infrrieure du s. maxillaire droit (flOche); B alors qu'il n'existe pas de pathologie muqueuse 6vidente ou de niveau tiquide darts ce sinus, on retrouve un 6paississement muqueux facilement visible dans le sinus maxillaire (pointe de flOche); C de surcroi't quelques celtutes ethmoi'dales moyennes sont opaques (pointe de flOche). Le sinus frontal gauche prrsente quelques zones de rrtention srcrrtoire visibles en hypersignal

cially when thickened. By knowing the location of s. linings the status of bony margins can be estimated. Frontal ss. The frontal ss. are absent at birth but develop in most individuals during the second year. An excavation extends upward from the bone beneath the medial margin of the orbital rim to form a cavity in the frontal r e g i o n and m e d i a l portion of the orbital roof. The two frontal ss. are rarely equal in extent and are separated near the midline by a bony septum. The bright signal on MR from the marrow cavity within the diploic space is sharply outlined by the normal cortical margin of the ss. The frontal ss. drain via the nasofrontal duct. Because o f the origin o f the frontal sinus from any o f the three ethmoid air cell groups, there is considerable variability in the nasal end o f the nasofrontal duct [1, 3]. The ethmoid ss. The ethmoid ss. lie between the orbits and nasal cavity. Axial and sagittal images permit division o f the ethmoid ss.

into anterior, middle and posterio r groups. The mucosal linings within the ethmoid ss. are easier to identify than within the frontal ss, Separation of the ethmoid ss. from the floor of the frontal ss. can be accomplished on the coronal and axial projections. At times sagittal projections are helpful when there is extension of the ethmoid ss. into the roof of the orbit, The medial walls of the ethmoid ss. present as bulges into the space lying lateral to the middle conchae. This central region is referred to as the ethmoid bulla and is composed of principally the middle ethmoid air cells. The middle ethmoid ss. together with maxillary ss. drain into the semilunar hiatus. A bony process descends from the anterior ethmoids to form an abortive forth concha lying between the ethmoid bulla and middle turbinate. This is the uncinate process which forms part of the lateral wall of the nasal cavity and the inferomedial margin o f the semilunar hiatus. It forms a recess into which the maxillary

ostium drains called the infundibulum. Secretions from the maxillary s. that have swept through the natural ostium pass over the superior margin of the uncinate process to enter the nasal cavity under the middle turbinate. Coronal views are best for visualizing this complex anatomy. The anterior ethmoids drain into the semilunar hiatus via the infundibulum in conjunction with the frontal ss. or by a separate ostium. Two or three posterior ethmoid air cells lie immediately anterior to the sphenoid s. and drain inferiorly into the recess of the superior conchae. Their separation from sphenoid ss. and middle ethmoid group is clearly visible on axial sections. M a x i l l a r y ss. T h e m u c o s a l linings o f the paired maxillary ss. are visualized because o f their intermediate signal as compared to the lack o f signal in the bony wall of the antrum. The outer margins o f the maxillary s. are surrounded by high signal areolar tissue in the

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Figs. 4 A-D~ 5 A-B Atypical mucocele. The patient is a 53 year old male with a 10 year history of maxillaryand ethmoid sinus disease, who failed to demonstrate any symptoms referable to the frontal s. A, B sinus plain films show the increased right frontal s. lucency (arrow) and expansion (arrow). Bony destruction is more clearly demonstratedby CT (C) and comparableMR (D). The presence of air within the lesion (double arrow) suggest the term "atypical mucocele". These findings were confirmed at surgery 5 At B. Osteoma. A 27 year old female was free of complaintsuntil one month prior to admissionwhen she developed excessive nasal secretions. ACT demonstratesa radiodense lesion in the most superior aspect of the right anterior ethmoid air cells at the drainage point of the nasofrontalduct (arrow) B This lesion is less well seen on the correspondingMR (arrow) 4 Mucoctle atypique. Patient de 53 ans prtsentant depuis 10 ans des manifestationssinusiennesmaxillairesethmo~dalessans sympttmes orientant vers les sinus frontaux. A, B Clichds standards des sinus montrantune augmentationde la transparenceet de la taille du sinus frontal droit (fldche). Une destructionosseuse est plus clairementd6montrdepar l'exploration scanographique(C) et IRM (D). La prtsence d'air h l'int6rieur de la 16sion (doublefl~che) sugg~re le terme de <>. Ces aspects ont ~t6 confirm6s ~ l'intervention chirurgicale. 50st6ome. Patient de 27 ans asymptomatiquejusqu'~t un mois avant son admission pour hypers6crdtion nasale. A L'exploration scanographique d6montre une 16sion hyperdense dans la pattie la plus haute des cellules ethmoidates antdrieures du c6t6 droit au contact du point de drainage du canal nasofrontal (flOche). B Cette 16sion est moins visible sur l'exploration en IRM (fldche)

infratemporat fossa. The remaining margins of the maxillary ss. are adjacent to the orbit, the alveolar ridge, and nasal cavities. Minor degrees of mucoperiosteal thickening can be easily detected. The natural ostium lies high and posterior on the medial wall. On coronal MRI it can be visualized lying lateral to the uncinate process under the protective cover of the middle turbinate. Sphenoid ss. The paired sphenoid ss. vary considerably in shape and extend into the floor of the middle cranial fossa or into the greater wing of the sphenoid. Bright signal from marrow is almost inva-

riably visible in the floor of the sphenoid s. and extending lateral and anterior into the base of the pterygoid planes. On sagittal sections this bright signal coming from medullary bone in shown to be continuous with the marrow cavity of the clivus. The cortical margins of the s. separate the pituitary gland from any pathological changes within the sphenoid s. In the floor of the sphenoid s. lie the pterygoid (Vidian) canals. These canals transmit the Vidian a. and n. The canals are trumpet shaped with a broad opening anterior and narrowing of the canal as it courses posterolaterally in the floor of the

sphenoid s. to join the foramen lacerum. The Vidian a. originates from the terminal branches of the m a x i l l a r y a.; thus, f o r m i n g a pathway from the pterygo-palatine fossa into the floor of the sphenoid s. They are visible on MR as regions of low signal surrounded by high signal marrow. The natural ostia of the sphenoid ss. lie in the anterosuperior wall of the s. This relationship is extremely important in differentiating tumor extensions into the sphenoid s., whether the route of spread has occurred through the natural ostium or through the pterygoid canal.

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Pathology Non-neoplastic conditions were all well shown on MR (Figs. 3-6). The MR information was equal to or superior to x-ray examinations in all cases except that of an osteoma of the ethmoid ss. (Fig. 5). In the remainder of the benign and malignant neoplastic conditions, MR was equal to or superior to the X-ray study (Figs. 7-9).

Discussion At first glance it would appear that magnetic resonance would not be suitable to examine the paranasal ss. Since cortical bone and air do not return a signal on MR, one might assume that CT or other x-ray procedures would be needed to adequately visualize the s. walls. Actually, most diseases affecting the paranasal ss. are primarily soft tissue abnormalities of the lining of these cavities rather than the bones themselves. Changes in the bony walls of the ss. are generally secondary manifestations of the mucosal disease. As a matter of fact, the sclerotic thickened margins of the ss. interfere with visualization of mucosa. If bone destruction is present, it is in reality a late mani-

festation of malignant disease of the mucosa. Deformed and displaced bony septa may contribute to or be the result of disease. MRI is actually an excellent imaging modality in this situation because bony septa are lined on either side by mucosa which gives a bright signal [2, 4, 5, 8, 10]. The encompassed bony septum can be visualized as a negative shadow, a lower signal between the layers of high signal soft tissue. While the mainstay for imaging inflammatory paranasal ss. disease wit1 continue to be plain x-rays because of their relative low cost, MR can now be substituted for CT scanning to evaluate advanced lesions in this area in most cases. With continued development of faster, lower cost MR scanners and the use of gadolinium DTPA, applications of magnetic resonance imaging of the paranasal ss. will continue to grow [7].

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nose and ethmoid sinus : imaging of the nasal cycle by MRI. Laryngoscope 98 : 928-933 Last RJ (t978) In : Anatomy : regional and a p p l i e d . 6 t h e d . C h u r c h i l l Livingstone, New York Lloyd GA, Lund VJ, Phelps PD, Howard DJ (1987) Magnetic resonance imaging in the evaluation of nose and paranasal sinus disease. Br J Radiol 60 : 957-968 Moore J, Potchen M, Waldenmaier N, Sierra A, Potchen EJ (1986) High-field magnetic resonance imaging of paranasal sinus inflammatory disease. Laryngoscope 96 : 267-271. Rauschning W, Bergstrom K, Pech P (1983) Correlative crauiospinal anatomy studies by computed tomography and cryomicrotomy. J Comput Assist Tomogr 7 : 9-13 Romer T, Tausch-Treml R, Harem B, Felix R, Wolf KJ (1988) Magnetic resonance tomography of paranasal sinus tumors using gadolinium-DTPA and multi-echo sequences. ROFO 149 : 171-177 Sore PM, Shapiro MD, Biller HF, Sasaki C, Lawson W (1988) Sinosal tumors and inflammatory tissues : differentiation with MR imaging. Radiology 167 : 803-808 Teresi LK, Lufkin R, Hanafee W (1988) Low cost MRI of the paranasal sinuses. Comput Med Imaging Graph 12 : 165168 Zimmerman RA, Bilanuik LT, Hackney DB, Goldberg HI, Grossman RI (1987) Paranasal sinus hemorrhage : evaluation with MR imaging. Radiology 162 : 499503

Received August 7, 1989~Resubmitted May 14, 1990~Accepted June I1, 1990