Received November 8, 1 991 ; accepted after revision April 1 6, 1992.1 Both authors: Department of Radiology, Medical College of Virginia Hospitals, MCV Station, Box 61 5, Richmond, VA 23298. Address reprint requests to F. J.

Lame.

849

AJR 159:849-857, October 1992 0361 -803x/92/1 594-0849 American Roentgen Ray Society

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Review Article

The Ostiomeatal Unit and Endoscopic Surgery: Anatomy,Variations, and Imaging Findings in Inflammatory DiseasesFred J. Lame1 and Wendy R. K. Smoker

Recent and ongoing advances made in endoscopic surgicaltechniques require the radiologist to understand the anatomy andpathophysiology of the paranasal sinuses and nasal passage.Endoscopy and CT are complementary procedures, and, as such,the normal anatomic relationships and their CT appearances needto be well understood in order for radiologists to offer continuedsupport as consultants to their clinical colleagues. In this article,we review the pertinent anatomy of the lateral nasal wall andparanasal sinuses, discuss the most frequently encountered nor-mal variations that may predispose a patient to inflammatorysinus disease, outline imaging protocols for evaluation of thisregion, and introduce the reader to current endoscopic surgicaltechniques. Last, the imaging findings in various inflammatoryprocesses involving the sinuses, as well as the local and regionalcomplications associated with paranasal sinus inflammatory dis-eases, are presented.

In our role as consultants, radiologists must keep abreastof clinical advances and be able to adapt imaging proceduresas necessary to meet changing clinical demands. Advancesin the understanding of mucociliary drainage patterns and thepathophysiology of paranasal sinus inflammatory disease,coupled with the availability of high-resolution CT and im-provements in endoscopic instrumentation, have led to majorchanges in the surgical management of sinusitis. As a result,the radiologist must relearn the anatomy of nasal and para-nasal structures, as well as the pathologic changes causedby diseases that affect this region, in order to correlate CTand endoscopic findings.

Normal Anatomy

The relationships between important bony and soft-tissuestructures and sinus ostia can be more easily understood andinterpreted on CT scans by first reviewing the anatomy of thelateral nasal wall and nasal septum.

Projecting from the lateral nasal wall are the inferior, middle,and superior turbinate bones (or conchae) (Fig. 1 A). Occa-sionally, a supreme turbinate bone can be identified. Beneatheach turbinate bone lies a respectively named meatus intowhich the various ostia drain (Fig. i B).

The inferior turbinate bone is the largest of the three, underwhich lies the inferior meatus. The inferior meatus receivesdrainage from the nasolacrimal duct, which is typically seenonly segmentally on axial scans. Occasionally, the duct canbe followed from its origin in the inferomedial aspect of theorbit to its ostium in the anteroinfenior aspect of the meatus,adjacent to the attachment of the inferior concha.

Under the superior turbinate bone, the smallest of the three,lies the superior meatus, through which posterior ethmoidalair cells drain via multiple ostia. This turbinate bone is identi-fled on coronal images as a slender structure, suspendedfrom the dome of the posterior aspect of the nose [i ]. Thesphenoethmoidal recess, draining the sphenoidal sinusthrough the sphenoidal ostium, lies posterosupenior to thesuperior turbinate bone, between the anterior wall of thesphenoidal sinus and the posterior wall of the ethmoidal sinus(Fig. 2). Lateral to the recess, the most posterior ethmoidal

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Fig. 1.-A, Line diagram of lateral nasal wallwith intact turbinate bones. Arrowheads = aggernasi cells, IT = inferior turbinate bone, MT =middle turbinate bone, ST = superior turbinatebone.

B, Line diagram of lateral nasal wall with tur-binate bones removed. Arrows = ostia and mu-cous flow patterns, I = drainage from frontalsinus, 2 = drainage from maxillary sinus, 3 =drainage from anterior and middle ethmoidal si-nuses, 4 = drainage from posterior ethmoidalsinuses, 5 = drainage from sphenoidal sinus. 1,2, and 3 drain to the middle meatus, whereas 4and 5 drain through sphenoethmoidal recess tosuperior meatus.

air cell (cell of Onodi) and the sphenoidal sinus share acommon wall, the sphenoethmoidal plate [2] (Fig. 2).

The middle turbinate bone covers the middle meatus, themost complex region of the lateral nasal wall. Near the su-perior attachment of the turbinate bone, a prominence of thelateral wall is produced by the agger nasi cells, the mostanterior ethmoidal air cells (Fig. 1). Above these cells lies thefrontal recess. The frontal sinus drains, via the frontonasalduct, agger nasi cells, and frontal recess, into the anterioraspect of the middle meatus, medial to the uncinate process,or directly into the ethmoidal infundibulum (Fig. 1 B). Theethmoidal infundibulum is often continuous with the fronto-nasal duct.

The middle turbinate bone attaches to two areas of delicatebone, which can pose potential problems during endoscopicmanipulation: the superior attachment to the delicate lateralaspect of the cribriform plate, and the lateral, intraethmoidalattachment, basal (or ground) lamella, to the thin laminapapyracea of the lateral ethmoidal wall (Fig. 3). Posteriorly,the basal lamella curves superiorly and becomes oriented inthe coronal plane, behind the ethmoidal bulla, thereby sepa-rating the anterior and posterior ethmoidal air cells. Ethmoidalair cells located anterior to the basal lamella will drain into themiddle meatus, whereas those cells located posterior to thebasal lamella will drain into the superior meatus [2].

If the middle turbinate bone is removed, three prominentunderlying structures are seen: the uncinate processanteriorly, the hiatus semilunaris, and the bulla ethmoidalisposteriorly. The uncinate process, a thin, hook-shaped, mu-cosa-covered bony prominence, originates anteriorly from theposteromedial border of the nasolacrimal duct. Almost parallelto the middle turbinate bone, it forms a free border thatdefines the anterior boundary of the hiatus semilunaris. Oncoronal CT, the uncinate process is easily detected as asuperior extension of the medial maxillary sinus wall, formingthe lateral wall of the middle meatus (Figs. 3 and 4). Lateralto the uncinate process lies the infundibulum, connecting theostia of the maxillary and ethmoidal sinuses to the hiatussemilunaris (Figs. 3 and 4). Mucociliary drainage from themaxillary sinuses courses superiorly, through the ostia andposterior infundibulum to the hiatus semilunaris, and eventu-ally into the middle meatus.

The hiatus semilunaris is bounded superiorly by the bullaethmoidalis, laterally by the bony orbit, inferiorly by the uncin-ate process, and medially by the middle meatus. It accom-modates multiple anterior ethmoidal ostia, and the singlemaxillary sinus ostium, to form the final segment of drainagefrom these sinuses. A superior extension of the hiatus semi-lunaris communicates with the sinus lateralis, the space be-tween the posterior wall of the ethmoidal bulla and the basallamella, providing drainage of this area and the middle eth-moidal air cells.

The bulla ethmoidalis, usually consisting of a single variableair cell, projects inferomedially over the hiatus semilunaris ina rounded fashion. The relationships of these three lateralwall structures are such that a channel is formed, linking thefrontal, anterior and middle ethmoidal, and maxillary sinusesto the middle meatus. This connecting channel is collectivelyreferred to as the ostiomeatal unit (OMU) (Figs. 3 and 4). Insummary, mucociliary drainage of the sinuses eventuallymerges into two common pathways, allowing division intotwo anatomic and functional groups [2]. The first group(frontal, anterior ethmoidal, middle ethmoidal, and maxillarysinuses) drains into the middle meatus, around the ethmoidalbulla (the OMU) (Fig. i B). This region is frequently involvedby inflammatory disease. The second group (posterior eth-moidal and sphenoidal sinuses), draining into the sphenoeth-moidal recess and superior meatus (Fig. i B), is less frequentlyaffected by inflammatory processes.

The nasal septum, easily identified on both axial and coronalCT, extends the entire length of the nasal cavity (Figs. 2 and4). The anterior portion is composed of cartilage, whereas theposterior portion is osseous, formed mainly by the vomer andthe perpendicular plate of the ethmoid bone. The interfrontalseptum anteriorly and the intersphenoidal septum posteriorlydo not always lie in the same plane as the nasal septum. Thisis an important anatomic consideration for endoscopic sur-geons.

Two important anatomic relationships between the para-nasal sinuses and adjacent structures must be mentioned.Awareness of the intimate relationship between the internalcarotid artery and the sphenoidal sinus is important for un-derstanding the potentially devastating complications of in-flammatory disease or endoscopy (Fig. 2). Bulging of the

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Fig. 2.-Axial CT scan obtained with inter-mediate windows shows sphenoethmoidal re-cesses (white dots) and proximity of carotid ca-nals (C) to lateral wall of sphenoidal sinus (5).Note also proximity of optic nerve (ON) to pos-terior ethmoidal (E) and sphenoldal sinuses. NS= nasal septum, arrowheads = sphenoethmoidalplate.

Fig. 3.-Line diagram of normal ostiomeatalunit Small arrowheads = basal lamella, large ar-rowhead = cribriform plate, dots = uncinate proc-

- *:#{149}#{149} -;: #{149}I,,. r

Fig. 4.-Coronal CT scan shows normal ostlo-meatal unit. Curved arrows = maxillary ostium,dots = infundibulum, straight arrows = middlemeatus, arrowheads = nasal septum.

AJR:159, October 1992 OSTIOMEATAL UNIT AND ENDOSCOPIC SURGERY 85i

ess.

carotid artery into the sphenoidal sinus is seen in 65-72% ofpatients [3-5]. The thin bone separating the artery from thesinus is less than 1 mm in 66% of patients, less than 0.5 mmin 88% of patients, and completely absent in 4-8% of cases[4, 5].

The location of the optic canal and nerve is an additionalimportant anatomic consideration. Because of the location ofthe distal canal opening, in 75% of cases the nerve will beclose to both the sphenoidal and ethmoidal sinuses [6] (Fig.2). During its course, the optic nerve bulges into the supero-lateral sphenoidal sinus wall, forming the optic eminence. Athin bony partition is present in 70-78% of patients [5, 7],and complete bony dehiscence is present in 3.6-4% of cases[5,8].

Anatomic Variations

The middle meatus and lateral nasal wall are subject towide normal variations that must be distinguished from path-ologic changes. These variations may, themselves, be theunderlying cause of recurrent sinus disease. However, thereis a lack of consensus among investigators with respect tothe prevalence and clinical significance of these variations, asthey have been encountered with similar frequency in patientsbeing scanned for sinus-related problems, as well as thoseundergoing evaluation for non-sinus-related problems [9].The more common variations can be divided into four groups,depending on the structures involved: middle turbinate bone,uncinate process, ethmoidal bulla, and nasal septum.

Middle Turbinate Variations

Concha bullosa.-The middle turbinate bone is usually athin plate of bone. When this plate becomes pneumatized byextension of the anterior (55%) or posterior (45%) ethmoidal

air cells, the air cell created is referred to as concha bullosa[9] (Fig. 5A). The reported prevalence of concha bullosaranges from 4% to 80%, depending on criteria for pneumati-zation and differences in study populations. True conchabullosa (pneumatization of both the vertical lamellar and infe-nor bulbous portions) is reported in 4-i 5.7% ofthe population[9, i 0]. If the definition is broadened to include any degree ofmiddle turbinate pneumatization, the prevalence increases to34% [1 1]. The highest prevalence (80%) is found in patientswith chronic sinusitis [1 2]. For this reason, some suggest thatconcha bullosa may be a contributing factor in the pathogen-esis of sinus inflammatory disease, although others do notshare this view [9]. Stammberger and Wolf [1 3] and Lidovand Som [i 4] reported that concha bullosa can, when suffi-ciently large, produce signs and symptoms by encroachingon the infundibulum. Concha bullosa may also contain polyps,cysts, pyoceles, or mucoceles.

Paradoxically curved middle turbinate bone.-Normally, theconvexity of the middle turbinate bone is directed medially,toward the nasal septum. When paradoxically curved, theconvexity is directed laterally, toward the lateral sinus wall(Fig. SB). A 26.i % prevalence of paradoxically curved middleturbinates has been reported [9]. Although no studies relatethis variation to sinus disease, it is a presumed etiologic factorbecause of the deformity and obstruction or alteration ofnasal passage air flow dynamics, especially when associatedwith other variations [i3].

Uncinate Variations

Deviation of the uncinate tip.-The superior aspect of theuncinate tip may deviate laterally, medially, or anteriorly outof the meatus, appearing as a second middle turbinate bone[i 3, iS]. When deviated medially, it comes into contact withand compromises the middle meatus. When deviated laterally,

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Fig. 5.-A, Coronal CT scan shows pneumatl-zation of middle turbinate bones bilaterally (con-cha bullosa), much greater on left (asterisk) thanon right. Also note nasal septal deviation, whichnarrows right middle meatus.

B, Coronal CT scan reveals paradoxically lat-erally curved middle turbinate bones bilaterally(dots). Also note pneumatization of right uncinatetip (arrow).

C, Coronal CT scan shows large Halle cells (H)projecting downward along roofs of maxillary si-nuses. Concha bullosa is seen bilaterally (aster-lsks). Sinuses, at this time, are clear.

D, Coronal CT scan shows evidence of eth-moidal bullae (asterisks) bilaterally without cvi-dence of associated sinus disease. Normal rela-tionship to ostiomeatal unit (dots) is well visualizedbilaterally.

it may encroach on the hiatus semilunaris and infundibulum,impeding drainage and ventilation of the anterior ethmoidal,frontal, and maxillary sinuses. The exact prevalence of thesevariations and their relation to sinus disease have not beendetermined.

Pneumatized uncinate tip (uncinate bulla).-The exactmechanism by which uncinate pneumatization (Fig. SB) oc-curs is not known. It has been proposed that this process isdue to growth of agger nasi cells into the most anterosuperiorregion of the uncinate process [9]. Studies reveal a prevalenceof 0.4-2.5% [9]. This variation has been implicated in narrow-ing of the infundibulum, producing impaired sinus ventilation[16].

Ethmoidal Variations

Halle cells-According to Kennedy and Zinreich [i 7], Hallecells, ethmoidal air cells that project inferiorly to the ethmoidalbulla into the floor of the orbit in the region of the maxillarysinus ostium, are encountered in 1 0% of the population (Fig.SC). However, Bolger et al. [9] defined Halle cells as any aircells located beneath the ethmoidal bulla, lamina papyracea,or orbital floor. Using this criteria, they reported a prevalenceof 45%. Although they found no significant difference in the

prevalence of Halle cells between patients scanned for chronicsinus disease and patients scanned for nonsinus reasons,Stammberger and Wolf [1 3] consider the presence of thesecells as another predisposing factor for recurrent maxillarysinusitis.

Large ethmoidal bulla.-The ethmoidal bulla can be soextensively pneumatized that it completely fills the sinus ofthe middle turbinate bone (Fig. SD). Stammberger and Wolf[1 3] reported that an enlarged ethmoidal bulla may contributeto sinus disease by obstructing the infundibulum or middlemeatus or by being primarily diseased and filled with pus,cysts, or polyps. The exact prevalence of an enlarged eth-moidal bulla is not known.

Agger nasi cells.-Agger nasi cells, the most constantethmoidal air cells, lie below the frontal sinus, inferolateral tothe lacrimal sinus, and represent pneumatization of the lacri-mal bone by extension of the anterior ethmoidal cells [i 0].They are located anterior and superior to the insertion of themiddle turbinate bone, along the lateral nasal wall [1 3] (Fig.iA). In anatomic dissection, the prevalence of the agger nasicell varies from 1 0% [18] to 89% [1 9]. Because of theirlocation near the lacrimal sac, involvement of these cells bysinus disease can lead to ocular symptoms. These cells mayprovide access to the frontal sinus and recess during endos-copy.

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AJR:159, October 1992 OSTIOMEATAL UNIT AND ENDOSCOPIC SURGERY 853

Nasal Septum Variations

Nasalseptaldeviation.-Normally, the structures that makeup the nasal septum are aligned to form a straight wall,extending from the cribriform plate superiorly to the hardpalate inferiorly (Fig. 4). At the junction of the nasal cartilageand vomer, acute bowing and deviation of the septum occurin 20% of the population [20]. When severe, the deviatedseptum may compress the middle turbinate bone laterally,narrowing the middle meatus and causing obstruction, sec-ondary inflammation, and infection (Fig. SA). When it is asso-ciated with swollen membranes, there is additional obstruc-tion to the normal flow of mucus from the sinuses.

Imaging Techniques

Radiologic evaluation is directed toward assessing the pa-tency of the maxillary sinus ostium, ethmoidal infundibulum,hiatus semilunaris, and middle meatus. Plain radiographs,widely available and inexpensive, provide insufficient detail toallow surgical planning. MR, with its excellent soft-tissuedetail, does not adequately depict the osseous sinus wallsand ostia. CT, because of its superb soft-tissue and bonedetail, remains the best technique for evaluating the presenceand extent of sinonasal disease before endoscopy.

The coronal plane provides the best demonstration of theOMU and simulates the plane seen by the endoscopist. Forscanning, the patient is prone with the head hyperextendedto ensure that free fluid layers along the maxillary sinus floorand does not falsely obliterate the OMU. Unenhanced 3- toS-mm-thick contiguous slices are obtained. Although originallyobtained with soft-tissue algorithms but filmed with soft-tissueand bone windows, our recent experience, as well as that ofothers [21 ], suggests that a single set of images obtained inbone algorithm and filmed with intermediate windows is suf-ficient in most instances. Contrast material, administered viaa bolus drip technique, is used only when assessing forcomplications of inflammatory disease. Occasionally, exten-sive dental amalgams may require thin-section axial scanningwith reformation in the coronal plane. Uncooperative patientsand those who are unable to maintain their head in hyperex-tension can also be examined in the axial plane. Imaging isbest performed after treatment of an acute process, so thatareas of residual disease, most likely responsible for recurringproblems, can be fully assessed [22, 23].

Endoscopic Surgery Techniques

Anterior rhinoscopy and indirect nasopharyngoscopy yieldlittle information regarding the middle meatus and the OMU[24]. Paranasal sinus endoscopy now permits accurate, directvisualization of the entire nasal cavity, middle meatus, OMU,and sphenoethmoidal recess. It can be performed as a purelydiagnostic procedure or as a therapeutic procedure (func-tional) to clear obstructed sinus ostia. Functional endoscopicsinus surgery is usually reserved for patients in whom medicalmanagement fails and who have OMU disease shown by CTand/or diagnostic endoscopy [23]. A fundamental knowledge

of endoscopic techniques is necessary for meticulous CTevaluation.

For diagnostic endoscopy, a 4.0-mm, 0#{176}and 30#{176}illumi-nated endoscope or a 2.7-mm, 30#{176}and 70#{176}illuminated en-doscope is used [24]. The endoscope is passed along thefloor of the nose while the septum, inferior meatus andturbinate bone, middle turbinate bone, and nasopharynx areevaluated. The instrument is then rolled over the inferiorturbinate bone into the posterior aspect of the middle meatusand drawn anteriorly as the ethmoidal bulla, hiatus semilu-naris, and OMU are evaluated [24]. Cultures and mucosalbiopsy specimens can be obtained, or antibiotics can beadministered, if indicated.

Currently, two functional endoscopic surgical approachesare used [1 8, 25]. Both are based on the conjecture that onceaeration of the sinuses is reestablished and normal drainageis restored, the mucosa will return to its prediseased state.The Wigand procedure, the more extensive and less com-monly used of the two, begins posteriorly with a sphenoido-tomy and proceeds anteriorly to the frontal recess. It involvesa total sphenoethmoidectomy and a supramiddle turbinateantrostomy to create surgical drainage of the ipsilateral si-nuses into the nose. The Messerklinger procedure begins atthe ethmoidal bulla and moves anteriorly to the frontal recessor posteriorly to the posterior ethmoidal and sphenoidal si-nuses, depending on the location of disease. This procedure,considered the true functional endoscopic surgical approach,relieves obstruction to the normal pathway of mucociliarydrainage.

Advantages of functional endoscopic surgery over moreconventional surgical techniques include (1 ) absence of skinor mucous membrane incisions and accompanying removalof intervening bone, (2) unparalleled visualization of the si-nuses of the lateral nasal wall, (3) more accurate diagnosis ofmalformations or obstructing masses producing refractorysinusitis, and (4) precise localization and removal of the siteof disease with mucosal preservation and restoration of nor-mal mucociliary drainage [1 8]. Endoscopy is limited in itsability to show frontal sinuses and recesses, maxillary sinusesand ostia, ethmoidal bullae, and posterior ethmoidal andsphenoidal sinuses. CT is, therefore, a complementary pro-cedure that ensures complete evaluation of changes causedby inflammatory paranasal sinus disease.

Inflammatory Sinus Diseases

Acute Sinusitis

Although occasionally due to a pure viral infection, acutesinusitis usually results from a bacterial superinfection, mostcommonly Streptococcus pneumoniae, Haemophllus influen-zae, and Staphylococcus aureus. A single sinus is typicallyinvolved, usually a maxillary sinus. When the frontal, eth-moidal, or sphenoidal sinuses are independently or addi-tionally acutely involved, risk of regional complications isincreased, and aggressive treatment is required. The radio-logic hallmark of acute sinusitis is the air-fluid level. Alterna-tively, CT findings may be limited to nonspecific, smooth or

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854 LAINE AND SMOKER AJR:159, October 1992

polypoid mucosal thickening. If the sinus ostium becomesobstructed, complete opacification may result.

Chronic Sinusitis

Chronic sinusitis is diagnosed clinically when the patienthas either persistent inflammation or repeated bouts of acuteinflammation. Anaerobes are more frequently implicated inchronic than in acute sinusitis [26]. CT may show mucosalthickening or opacification, but the hallmark of chronic sinus-itis is osseous thickening of the sinus wall, representingremodeling and new bone formation in response to persistentinflammation [26] (Fig. 6). The prevalence of complicationswith chronic sinusitis is increased, including mucous retentioncysts, polyps, and mucoceles. Although CT permits evalua-tion of the complications of chronic sinusitis, more importantlyit shows the pathologic changes responsible for the chronicdisease (e.g., obstructed ostium, apical tooth abscess). Inaddition to inflammatory disease, occasionally tumors may beresponsible for recurrent disease. MR evaluation has beenshown to be useful in this regard. Most sinus tumors, exceptneuromas and minor salivary gland tumors, are homogeneousand have intermediate signal intensity on T2-weighted im-ages, as compared with the inhomogeneous high signal inten-sity of most inflammatory tissue [27].

Allergic Sinusitis

Allergic disease, a systemic process with a tendency forsymmetric sinus involvement and pansinusitis [28], affects10% of the population. CT often shows bilateral mucoperios-teal polypoid thickening of the sinus and turbinate membranes(Fig. 7). Air-fluid levels are typically absent unless associatedacute bacterial superinfection occurs. Polypoid thickening ismore often seen with allergic disease than with bacterialinfection [29], resulting from persistent membrane hyperpla-sia.

Fungal Sinusitis

Although uncommon, a variety of fungal diseases involvethe sinonasal cavities. Mucor and Aspergillus, both part of

the normal respiratory flora, are the pathogens most com-monly encountered. Although radiologically similar, they canfrequently be differentiated clinically. Mucormycosis, an ag-gressive, highly invasive disease, occurs mainly in an immu-nocompromised or diabetic (50-75%) host. Aspergillus, how-ever, can produce infection in otherwise healthy persons bycolonization of a paranasal sinus. An allergic form of asper-gillosis has also been described, associated with asthma andrecurrent nasal polyps. Invasive aspergillosis occurs primarilyin immunocompromised persons and progresses, like mucor-mycosis, to produce necrosis, vascular thrombosis, and intra-cranial extension. Initially, both cause nodular mucoperiostealthickening, which eventually coalesces to opacity an entiresinus (Fig. 8). Multiple focal areas of bone destruction, occur-ring in later stages, may mimic an aggressive tumor. However,in contrast to tumors, areas of bone thickening and sclerosismay also be detected (Fig. 8). Regions of high density withinthe opacified sinus on CT are highly suggestive of fungalinfection [30-33] (Fig. 8A). These dense concretions may bethe result of the combination of metal ions and calcium saltsknown to occur in fungal mycetomas. Recent studies [32]suggest that MR may be more specific than CT for diagnosingfungal sinusitis. The presence of ferromagnetic metallic ionsproduces a hypointensity on Ti- and T2-weighted images(Fig. 8C). In addition, MR more effectively shows the multipleintracranial complications of fungal diseases such as cavern-ous sinus thrombosis, arterial involvement, and skull baseinfection [34, 35].

Granulomatous Sinusitis

A variety of diseases can produce granulomatous changesin the sinonasal cavities. Actinomycosis, syphilis, tuberculosis,and sarcoidosis have all been reported [29], but Wegenersgranulomatosis and midline granuloma are most familiar. We-geners granulomatosis, a small-vessel necrotizing vasculitis,includes involvement of the sinuses, tracheobronchial tree,and kidneys. Midline granuloma, thought to be a lymphore-ticular disease, has recently been described, and is beingreported with increasing frequency in cocaine users [36].Granulomatous diseases initially involve the nasal cavity and

Fig. 6.-Chronic sinusitis. Axial CT scan showstotal opacification of left maxillary sinus withmarked thickening of lamina dura (arrowheads)compared with normal right sinus wall.

Fig. 7.-Polypoid disease. Coronal unenhancedCT scan shows complete opacificatlon of rightmaxillary sinus with nearly complete opacificationof left maxillary sinus. Mucosal thickening of tur-binate bone and nasal passage (dots) contributesto obstruction. Biopsy revealed polypoid muco-periosteal thickening.

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Fig. 8.-Fungal sinusitis.A and B, Axial CT scans show soft tissue filling right maxillary, ethmoidal, and sphenoidal sinuses. Lesion is heterogeneous; increased density is

suggestive of fungal infection with calcium and/or metals contained within mycetoma. Lamina dura of right maxillary sinus is slightiy thickened comparedwith left, indicative of chronic disease (arrowheads, A). However, at higher level, there is evidence of sinus expansion and osseous destruction involvingboth right lateral ethmoidal wall and right posterolateral sphenoidal sinus wall (arrowheads, B).

C, Coronal contrast-enhanced Ti-weighted MR image reveals heterogeneous enhancement of lesion. Areas of marked hypolntensity (asterisks)represent signal void effects of calcium and metals contained within mycetoma. This appearance on MR images is highly suggestive of fungal disease.

AJR:159, October1992 OSTIOMEATAL UNIT AND ENDOSCOPIC SURGERY 855

Fig. 9.-Mucocele. SagittalTi-weighted MR im-age shows a mass within frontal sinus that hasexpanded the sinus and is isointense with mucosalmembranes.

Fig. iO.-Mucocele. Coronal Ti-weighted MRimage shows mass occupying ethmoidal sinuswith bony expansion of lateral walls. Mass is hy-perintense relative to mucosal membranes and,when compared with mass seen in Fig. 9, exem-plifies variable appearance of mucoceles on MRimaging.

septum primarily and the paranasal sinuses secondarily [37].Although Wegeners granulomatosis may cause extensivebone loss, without an associated mass [38], CT generallyshows bulky, bilateral soft-tissue nodules lining the mucosaof the nasal cavity and septum. Advanced cases involvedestruction of the cartilaginous nasal septum and osseousstructures.

Local Complications of Sinusitis

Inflammatory polyp-Mucous membrane hyperplasia fromchronic inflammation is thought to be the underlying cause ofinflammatory polyps. The hyperplasia is usually allergic inorigin, most commonly located in the nasal cavity or maxillarysinus. CT typically shows a homogeneous soft-tissue mass.When severe, polyps may cause obstruction, leading to in-

spissated secretions and expansion of sinus walls. At thispoint, they may resemble tumors, and distinction on CTbecomes difficult. As mentioned, MR has been shown to aidin this differential diagnosis [27].

Mucous retention cyst-Mucous retention cyst, a benignlesion commonly occurring in the maxillary sinus floor, repre-sents inflammatory obstruction of a seromucinous gland ofthe sinus mucosal lining. CT typically shows a homogeneous,dome-shaped, non-gravity-dependent soft-tissue mass withsharply defined margins.

Mucocele.-Mucoceles result from obstruction or septatedsequestration of a portion of a sinus cavity. These collectionsresult not only from inflammation but also from posttraumaticor neoplastic obstruction. The sinus fills with secretions, andeventually benign expansion occurs. Sixty percent of muco-celes occur in the frontal sinus, 30% in the ethmoidal sinus,and 10% in the maxillary sinus [37]. Sphenoidal mucoceles

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are rare. CT shows a low-density, nonenhancing mass thatfills or expands the sinus. On both Ti - and T2-weighted MRimages the signal varies considerably, from hypointense tohyperintense depending on the concentration of water, pro-tein, and mucus [39, 40] (Figs. 9 and 10). An enhancing rimwith heterogeneous density suggests a mucopyocele, aninfected mucocele [38, 41].

Regional Complications of Sinusitis

Regional complications may result from frontal, ethmoidal,or sphenoidal sinusitis. In particular, in one study, ethmoidalsinusitis was the cause of acute orbital inflammation in 75%of patients [42]. These infections may travel via an extensivesystem of valveless veins through the thin, occasionally de-hiscent lamina papyracea. Orbital cellulitis, subperiosteal ab-scess, retrobulbar abscess, or optic neuritis may result. Dis-tinction between postseptal abscess and cellulitis, usuallypossible on CT scans, is important, as treatment protocolswill differ (Fig. 1 1). Cellulitis is characterized on CT by diffuse,homogeneously increased density and treated medically. Onthe other hand, abscesses characteristically have a centrallow-density area on CT and usually require both externalethmoidectomy and prolonged antibiotic therapy. Involvement

of the intraconal space (orbital phlegmon) typically is mani-fested as an increased density of the retrobulbar fat (dirtyfat).

An additional complication of sinus inflammation is regionalosteomyelitis, most commonly involving the frontal bone[26]. Infection can spread hematogenously, via diploic veins,or by direct extension. Extensive therapy is required. Frontalosteomyelitis, termed Potts puffy tumor, causes lytic destruc-tion of the frontal bone associated with an extracranial soft-tissue mass [43].

Intracranial Complications of Sinusitis

Intracranial complications of sinusitis, commonly due toextension of frontal, ethmoidal, or sphenoidal disease, includemeningitis, subdural and epidural empyema, brain abscess,and venous sinus thrombosis. Spread of infection can occuralong several routes: (1 ) hematogenous, (2) perineural, (3)retrograde thrombophlebitis, or (4) direct inoculation (traumathrough an infected sinus) [26]. Complete head CT withcontrast enhancement or MR examination is required whenintracranial complications are suspected, as the infection maylocalize in areas distant from the primary infection.

Fig. 1 1.-Orbital complications of inflammatorysinus disease.

A, Axial contrast-enhanced CT scan shows ahypointense postseptal collection containing airadjacent to opacified left ethmoidal air cells. Thissubperiosteal abscess required surgical interven-tion. Note marked edema of left medial rectusmuscle (dots). Preseptal cellulitis (asterisk) andslight proptosis are also apparent.

B, Axial contrast-enhanced CT scan in a differ-ent patient shows homogeneously increased den-sity involving both pro- and postseptal space ofright orbit. There is also a suggestion of slightproptosis and cellulitis. This case resolved withmedical management alone.

Fig. i2.-Cystic fibrosis.A and B, Axial (A ) and coronal (B) CT scans

show heterogeneous, polypoid opacification ofparanasal sinuses and nasal cavity. Thickening ofmaxillary sinus lamina dura indicates chronic,long-standing disease (arrowheads, A ). There ispressure erosion of medial wall of left maxillarysinus and expansion of left nasal cavity. Ethmoidalsinuses are expanded bilaterally, left greater thanright. Note pressure erosion of lamina paparyceain several areas bilaterally.

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AJR:159, October 1992 OSTIOMEATAL UNIT AND ENDOSCOPIC SURGERY 857

Syndromes

Systemic syndromes in which sinusitis is a component areinfrequent but well described. The syndromes most frequentlyencountered are Kartageners syndrome (immotile-cilia syn-drome) and cystic fibrosis (mucoviscidosis). The primary de-fect in Kartageners syndrome is a functionally inefficientcentral core of epithelial cell cilia that leads to inspissatedsinus secretions [44]. Cystic fibrosis, on the other hand, is aninherited disorder involving a fundamental dysfunction of ex-ocrine glands that results in the secretion of thick, tenaciousmucus [45].

Although the causes of these syndromes differ, their CTappearances are similar. Almost universal opacification of alldeveloped paranasal sinuses occurs. The secretions are fre-quently dense, reflecting the chronic inspissated state, withvariable concentrations of mucoproteins and fluid. When thedisease is long-standing or associated with polyps, sinusenlargement can occur, leading to bone remodeling and facialdeformity (Fig. 12).

Summary

Endoscopic paranasal sinus surgery is consistently gainingmomentum in the diagnosis and treatment of sinus disease.Otolaryngologists are now capable of visualizing and treatingall sinus drainage passages on an outpatient basis. High-resolution CT has become an important complementary pro-cedure to sinus endoscopy. The normal anatomy and varia-tions of sinus structure, as well as pathologic appearancesand complications of sinus disease, need to be well under-stood by the radiologist to provide optimal patient care.

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