High Resolution CT with Image Reformation in Maxillofacial Pathology

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1 3 1 High Resolution CT with Image Reformation in Maxillofaial Pathology Mihael N. rant-zawadzki1 Hideyo Minagi 1 Mihael P. Federle 1 Lee D. Rowe 2 Twenty-four patients with maxillofaial pathology were examined with omputed tomography (CT) using thin ( mm) setions allowing omputer reformation of images in multiple planes. Eight patients also had pluridiretional tomography. The patients inluded 14 with faial trauma, four with aute paranasal sinus infetions, and six with suspeted neoplasms. High resolution CT with reformations allowed thorough evaluation of faial trauma. Frature sites were orretly identified, as were the relation of fragments to vital strutures. The form of strutural faial alteration was easily assessed, optimizing the presurgial plan for reonstrution. In addition, CT allowed simultaneous evaluation of assoiated brain injury. In aute infetious proesses and neoplasms, CT defined the extent of involvement and direted the type of therapy. In both situations, aurate assessment of bony destrution permitted definitive planning for bony debridement in infetion and helped in the differentiation of benign from malignant proesses in neoplasia. Density determination also allowed differentiation of neoplasti soft tissue from inspissated muus within obstruted sinuses. Experiene suggests that CT an be the definitive imaging method in the diagnosis of omplex maxillofaial pathology when suffiient evaluation is unavailable from plain films. It was superior to thin-setion pluridiretional tomography in several instanes. This artile appears in the January / February 1982 issue of JNR and the Marh 1982 issue of JR. Reeived pril 9,1981 ; aepted after revision ugust 7, Presented at the annual meeting of the merian Soiety of Neuroradiology, Chiago, pril Department of Radiology, University of California, San Franiso Shool of Mediine, San Franiso General Hospital, San Franiso, C ddress reprint requests to M. rant-zawadzki. 2 Departm ent of Otolaryngology, Uni ve rsity of California, San Franiso Shool of Mediine, San Franiso General Hospital, San Franiso, C JNR 3:31-37, January / February / 82/ $00.00 merian Roentgen Ra y Soiety oth onventional and omputed tomography (CT) an provide important radiologi informati on for evaluation of maxillofaial path ology. The inherently superior ontrast resolution of CT has establi shed it as th e method of hoie in the staging of maxillofaial neoplasm and in the evaluati on of hroni in fl ammatory proesses in th e paranasal sinuses [1-5]. However, the spati al resolution of CT has lagged behind th at of pluridiretional tomography until reently [6]; thus CT has had limited use in th e evalu ati on of maxill ofaial trauma in wh ih visualization of bony detail is important. reent report from this institution suggested th at third generati on CT has th e potential for supplanting onventional tomography in the evalu ation of faial trauma [7]. Sine th at report, further advanements in CT tehnology have allowed very thin setion sanning, thus improving spatial resolution. In addition, newer software pakages all ow great flexibility of data manipulation permitti ng image reformati on in multiple pl anes and reg ion-of-interest density analysis. These refinements have expanded the potential utility of CT in maxillofaial trauma and other pathology. We report our early experi ene with this enhaned apability of CT sanning. Subjets and Methods We examined 24 patients w ith maxillofa ial abnormalities. ll CT sans were perform ed on a General Eletri 8800 sanner, using either 1.5 mm ontiguous seti o ns, or 5.0 mm setions spaed 3.0 mm apart produing a 2.0 mm overl ap o f adjaent sans. Image reformation in multiple planes was performed via prototype software pakage supplied by the G.E. Corporation.

2 32 RN1-Z WDZKI ET L. JNR:3, January/ February 1982 Fig. 1.- Tripod frature of right maxilla., Sequential axial CT setions. Posteroinferior separation of zygoma from right maxill a (large arrow); fratures of zygomati arh, frontozygomati suture (urved arrow), and medial orbital wall (small arrows)., Coronal reformation verifies tripod frature with posteroinferior displaement of malar eminene. C, Soft-tissue window setting. No herni ation of the inferior retus musle (arrow). Fourteen patients were evaluated for faial traum a, two of whom were speifiall y studied for erebrospinal fluid (CSFl rhinorrhea several months after injury. Four patients were examined for aute infetion; six others were evaluated for suspeted tumors. Five of th e trauma patients, one of the infetion pati ents, and two of the tumor pati ents also had studies with pluridiretional tomography using mm setions. The onventi onal tomograms were retrospetively reviewed independently by one of us (H. M.l, and findings were ompared to the original interpretati on of the CT study. We attempted to evaluate th e on tri bution of th e diagnosti inform ati on obtained by CT to the th erapeuti approah and linial outome in eah ase. Results Trauma ute blunt trauma to the fae in nine patients resulting in omplex fratures was studied by CT. CT identified tripod fratures in seven patients. It showed th e assoiated orbital floor fratures in all seven, and in three signifiant inferior retus herni ati on was depi ted (two of whom had diplopia). In one patient, these findings were superimposed on a omplex Le Fort II frature; both omponents of the injury were read il y diagnosed. CT also showed multifoal maxi ll ary sinus fratures, nasal fratures, and medial orbital blowout fratures in these patients. Multiplanar im age reformation in ombination with thin axial uts was espeiall y valuable. It all owed three-dimensional display of bony distrations and the resulting displaement of the malar eminene in tripod fratures (fig. 1). Wh en the zygomati arh showed no frature or on ly a single, nondisplaed one, the displaement of the malar eminene was mini mal. In another patient, expeted posterior displaement of the mid fae in the Le Fort II injury was minimal, as the usual pterygoid frature omponent was absent (fig. 2). Subtle orbital floor fratures were best seen on im age reformations in a plane defined by the inferior retus musle. Herni ation of that musle, when present, was best seen in a plane perpendi ular to its ourse (fig. 3). CT fully evaluated omplex fratures of th e superior orbital rim region involving frontal and ethmoid sinuses in two additional patients and in the patient with a Le Fort II / tripod frature mentioned above. Reformations of axial im ages again proved useful. Impingement on the superior retus musle was delineated in two, while in one ase ompression of the globe by fragments aounting for ophthalmoplegia was defined. These findings were diffiult to asertain on axial uts alone. Two of these three patients with frontal sinus fratures also had distration of the posterior wall, seen on both axial (Fig. 2) and sagittally reformatted images. Gunshot injury was thoroughly evaluated with CT in three patients. Loation of bu ll et and bone fragments, assoiated bony disruptions, and intraranial penetration were easy to appreiate. The integ rity of any struture lying in the pl ane originally sanned (axial) was best evaluated on reformations perpendiular to it. Two patients were speifially studied for CSF rhinorrhea several months after blunt faial trauma. The first had meningitis. xial 1.5 mm uts showed no definite abnormality. However, sagittal and oronal reformations revealed a 5.0 mm defet in the fovea ethmoidali s with an assoiated

3 JNR:3, January / February 1982 REFORMTTED CT OF MXILLOFCIL PTHOLOGY 33 Fig. 2.-Le Fort II frature after blunt faial trauma., Seleted axial CT setions. Fratures of in ferior orbital rim s at in fraorbital foramen level bilaterally, minimally displ aed maxillary wall fratures elsewh ere (arrows ), and medial orbital wall disruptions harateristi of Le Fort II injury. ssoiated right subdural hematoma (arrowheads ) and posterior wall frontal sinus frature., Coronal reformation. Fratures (arrows ). More posterior reform ations (not shown) found no pterygoid fratures, possibly aounting for relative lak of posterior displaement of mid fae. 8 enephaloele (fig. 4). Surgery orreted the defet. The seond patient had an inonlusive radionulide searh for a CSF fistula and negative pluridiretional tomography. CT metrizamide study suggested posterior ethmoid CSF leak. This study and persistent rhinorrhea prompted surgial exploration; no obvious defet was seen in the dura of the ribriform plate. lthough the region was paked with musle at surgery, CSF rhinorrhea reurred 2 months later and neessitated shunting of CSF from the subarahnoid spae into the peritoneum. Early in our experiene, five of the trauma group patients had pluridiretional tomography in addition to CT. In this small group, CT provided as muh as or more information than did the onventional tomographi study. In addition to defining more faial (espeially maxillary) fratures than onventional tomograhy, CT showed a temporal bone frature not seen with pluridiretional tomograhy in one ase and ruled out a lesser sphenoid wing frature suspeted on pluridiretional tomography in another. CT did miss one nondisplaed horizontal frature of the lateral pterygoid plate whih was seen with polytomograhy in a patient with tripod frature. CT defined brain parenhyma hematomas in two patients and a subdural hematoma (fig. 2) in a third, information unsuspeted linially and unavailable from onventional radiography. Infetion Four patients had aute sinusitis. Two developed fulminant maxillary sinusitis after tooth extration. The first had a CT study that defined maxillary antral wall dehisene at several sites indiating osteomyelitis. Image reformations revealed dehisene of the orbital floor and extension of the proess into the lower retroorbital spae (fig. 5), informati on not definitely supplied by axial uts alone. These findings preeded ophthalmoplegia whih developed th e next day and led th e surgeon to a speifi explorati on and drainage of this region and th e adjaent ethmoid ell s, allowing rapid linial improvement. The seond pati ent had a draining sinus from his lateral orbital border. CT defined extension of a maxillary infetion into the right superior ethmoid sinus and dehisene of the lateral floor of this sinus with ommuniation into the orbital roof. Coronal image reformation best showed the lateral spread aross the roof of th e orbit, explaining the drainage at the lateral anthus. third patient developed pansinusitis during a 2 week intensive-are-unit hospitalization after abdominal trauma; CT defined the involvement and helped rule out intrarani al extension as a ause of his waning mental status. Th e fourth patient showed signs of a mild maxillary sinusitis. Pl ain film s revealed a molar tooth in the maxill ary antrum. CT defined an infeted bony yst ontaining the tooth with erosion of the maxillary walls and orbital floor by this proess (fig. 6). n infeted dentigerous yst was found at surgery. Removal was greatly failitated by knowledge of extension into th e infratemporal fossa and orbital floor. Tumors Si x patients were studied for maxillofaial neoplasms. Two had aggressive arinomas of the paranasal sinuses. Extension of th ese neoplasms into orbital and intrarani al spaes was thoroughly demonstrated with multipl anar image reformation. ony destrution was easily assessed. One patient was studied for an intranasal mass. tomographi study in this patient showed diffuse opaifiati on within the nose and paranasal sinuses. CT density measure-

34 RNT-ZWDZKI ET L. JNR :3, January / Febru ary 1982 o Fig. 3. - 0 rbital frature with inferior retus herniation., Sequential axial CT setions.

4 34 RNT-ZWDZKI ET L. JNR :3, January / Febru ary 1982 o Fig rbital frature with inferior retus herniation., Sequential axial CT setions. Fratures of nose (large arrow), lateral maxillary antral wall, and lam ina papyraea (urved arrow). Inferi or retu s musle in left maxillary antrum (small arrows) suggests herniation. S, Reformation along plane of inferi or retus mu sle verifies its depression. C, Plane truly orthogonal to this musle disloses extent of orbital floor displaement. D, Conventional tomograms. Orbital fl oor frature with inferior displaement of soft tissues. ment revealed that th e maxillary " soft tissue" measured 20 Hounsfi eld units (H) below the nasal soft tissue (fig. 7). This suggested blokage of sinus drainage rather than antral tumor extension ; the lak of obvious bony destrution also supported a benign inflammatory disorder. Surgery verified all ergi polyposis. One patient had a parotid tumor assessed with CT. one destrution and extension medial to the mandible was ruled out. noth er patient had a glabellar tumor. CT showed no evidene of bony destrution, but delineated extension of thi s tumor into the medial orbit, where image reformations proved that the growth displaed (but did not involve) the globe and penetrated the nasal-larim al dut ausing its expansion. iopsy showed a benign mesenhymal tumor. The final patient was a woman with a hard mass felt in the superior medial orbit. CT demonstrated soft-tissue density arising from the ethmoid sinus bulging into the orbit. ony thinning and apparent erosion was noted. Differentiation between malignant and beni~n proess ould not be made. muoele was found at surgery. Disussion The diagnosti usefulness of maxillofaial CT depends on the type of disease. In major faial trauma, not only is the delineation of fratures important, but a three-dimensional understanding of gross strutural alterations is desirable for proper osmeti reonstrution. CT image reformation into oronal and sagittal planes was useful in this respet; reformation along planes ontaining strutures suh as the

5 JNR:3, January/ February 1982 REFORMTTED CT OF MXILLOFCIL PTHOLOGY 35, ~t::..._ ~. ' J~ $ ~. Fig. 4.- Traumati CSF fi stut a with meningitis., Contiguous 1.5-mm-thi k axiat CT setions through ethmoid region. Only minimal right anterior ethmoid opaifiation (arrows ). Coronal () and sag ittal (not shown) reformations through ethmoid roof in this reg ion depi ted bony defe t and assoiated small enephaloele. C, Conventional tomog raphi study obtained initially. Soft tissue in right ethmoids and erosion of ethmoid roof. Fig. 5.-Sinus infetion and osteomyelitis after tooth extration., Sequential axial CT setions. Multifoal bone resorption of maxillary antrum fl oor and wall s., Coronal reformation. Destru tion of orbital fl oor and extension of inflammation in to retroorbital fat (arrows ). C, Conventional tomographi study 1 day before CT. Maxillary sinus and ethmoid opaifiation seen; bony involvement suggested. Orbital findings on CT atually preeded linial development of ophthalmoplegia by 8 hr and altered surgial treatm ent (see text).

36 RNT-ZWDZKI ET L. JNR:3, Jan uary I February 1982 Fig. 5.-Dentigerous yst in maxillary sinus., Tooth-shaped density near maxill ary roof (arrow)., xial CT setion.

6 36 RNT-ZWDZKI ET L. JNR:3, Jan uary I February 1982 Fig. 5.-Dentigerous yst in maxillary sinus., Tooth-shaped density near maxill ary roof (arrow)., xial CT setion. Cystli ke struture (arrows) expands maxillary antrum, eroding its posterior wall. C, Reformation along midsag ittal orbital plane shows extent of yst to level of orbital floor. Surgery ve rified dentigerous yst. Fig ll ergi polyps suggesting neoplasm; soft-tissue mass protruding out of nares., Conventional tomogram. Opaifiation of nasal and maxillary antral avities; evidene of bony erosion was equivoal., xial CT setions. Soft ti ssue within nose and maxillary antra extends into ethmoids. Thikening of maxillary antrum wall s suggested hroni proess; no bony erosion was noted. Density analysis revealed CT numbers with in maxillary antrum to be 25 units less than those of nasal soft tissue, suggesting obstruti on of sinuses, rather than tum or invasion. iopsy dislosed allergi polyp. opti nerve or inferior retus musle was speifially helpful. In addition, rapid evaluation of damage to vital strutures, suh as the globe and opti nerve, or assoiated brain injury is ru ial and is diretly obtained through the superior ontrast resolution of CT. urate early diagnosis is vital, beause delayed ompli ations of unreognized injury suh as diplopia, mu oele, osmeti disfigurement, and meningitis are serious and diffiult to treat. Further, the omplex faial skeleton requires a tehnique with high spatial resolution for evaluating subtle but important disruptions in its framework when plain films are equivoal. CT offers ertain advantages over pluridiretional tomography in regard to gross bone trauma and soft tissue injury. To reonstru t a three-dimensional image from onventional tomograhi uts in two projetions oneptually is diffiult. Pati ent positioning affets interpretation of arhitetural derangements, sine rotation may simulate strutural displaement. Multipliity of frag ments in gross trauma an ause " ghost" artifats due to superimposition of blurred images onto the plane of setion lead ing to oasional misinterpretation of fratures with onventional tomography [7, 8]. Diret visualization of soft-tissue strutures is the forte of omputed tomography. In our earlier experiene, one-third of patients with maxillofaial trauma had assoiated intraranial findings [7] that CT reognized. Of our urrent 14 patients with trauma, five had findings of some importane relating to the intraranial ontents (hematoma, enephaloele, frontal sinus-brain ommuniation). Subtle faial trauma tests CT sensitivity. The ability of CT to detet orbital floor, maxillary, and ethmoid wall fratures (some missed with pluridiretional tomography) in our series shows that thin setion CT shows even subtle fratures. Image reformation in planes perpendiular to that of the bone in question (e.g. orbital floor, fovea-ethmoidalis) are key to the diagnosis. Yet the tehnique has its limits. Thus, thin frature:;; in the plane being sanned may be missed when insuffiient distration exists to visualize them on axial or reformatted images. lso, patient motion detrats from image spatial resolution, espeially on image reformations. Short tube-ooling intervals are needed for rapid sequene sanning and are allowed with low milliampere settings without loss of resolution in bony strutures, although some

JNR :3, January/ Febru ary 1982 REFORMTTED CT OF MXILLOFCIL PTHOLOGY 37 loss of soft-tissue resolution ours. Yet in none of our ases did these minor limitations affet either therapy or linial outome.

7 JNR :3, January/ Febru ary 1982 REFORMTTED CT OF MXILLOFCIL PTHOLOGY 37 loss of soft-tissue resolution ours. Yet in none of our ases did these minor limitations affet either therapy or linial outome. The savings in radiation dosage offered with CT are appreiable. single 1.5 mm setion at a 320 m setting with a 3 se pulse width delivers about 4 rad (0.04 Gy) at the entrane site in the patient's fae (in our experiene, the amperage and pulse width settings an be even lower without signifiant loss of bone resolution). Setions 5 mm thik with 3.0 mm spaing result in 2.0 mm of overlap. This tehnique doubles the speed of the study while allowing suffiient resolution on image reformation for aurate diag nosis. Even with this overlap tehnique, total radiation dosage to any setion of the patient's fae is less than 9 rad (0.09 Gy) [9]. Total examination time in our patients varied from 20 to 40 min depending on the number of setions needed to over the region of interest, and the amperage/ pulse-width seleted. In ontrast, a onventional set of 4-mm-thik faial tomograms in two projetions neessitates up to 15 uts in eah of the two planes. Sine radiation passes through all anatomi layers of the head irrespetive of whih layer is in fous, a dose of about 30 rad (0.3 Gy) to the faial region an result [6]. In younger individuals, radiation onsiderations might be a fator in preferring omputed tomography. The usefulness of CT in faial infetion and neoplasia rests mainly on its ability to delineate extent of the proess into various anatomi ompartments, to detet bony destrution, and to provide densitometri analysis. In all three areas, CT IS uniquely valuable by virtue of its superior ontrast resolution and its multiplanar viewing apability [10]. However, mirosopi infiltration into surrounding ti s sues will still ause errors in assessment of tumor and infetion extension. lso, extremely thinned bony strutures may be falsely assumed to be eroded due to density averag ing of adjaent soft tissues in the tomographi setion, as in our muoele patient. Further, some tumors may have areas of nerosis; thus, density measurement alone for differentiating neoplasti soft tissue from inspissated muus within a sinus may not be dependable. On the basis of this early experiene, our urrent approah to the evaluation of maxillofaial disease involves CT as the first diagnosti method after plain films. Not all patients with trauma or other maxillofaial pathology need a tomographi study for thorough evaluation, but we find CT espeiall y helpful in evaluating omplex faial trauma where two or three different ategories of frature oexist. Diret visualization of inferior retus herniation helps th e thorough diagnosis and surgial approah to patients with orbital blow-out injuries as well. lthough image reformation is urrently tedious, software pakages that automatially reformat axial images into any hosen plane at a designated distane interval are now beoming avail able. This should greatly redue the amount of omputer interation required. We urrently reserve pluridiretional tomography for suh fine detail work as orbital foramen views and inner ear evaluation. It is possible that further innovations in CT tehnology will obviate onventional pluridiretional tomography in these appli ations as well. REFERENCES 1. Parsons C, Hodson N. Computed tomography of paranasal sin us tumors. Radiology 1979;132: Forbes WStC, Fawitt R, Isherwood I, et al. Computed tomography in the diagnosis of diseases of the paranasal sinuses. Clin Radiol 1978;29 : Takahashi M, Tamakawa Y, Shindo M, et al. Computed tomography of th e paranasal sin uses and th eir adjaent strutures. Comput Tomogr 1977;1 : Hesseli nk JR, Weber L, New PFJ, Davis KR, Roberson GH, Taveras JM. Evalu ation of muoeles of the parana sal sin uses with omputed tomography. Radiology 1979; 133: Som PM, Shugar JM. ntral muoeles: a new look. J Comput ssist Tomogr 1980;4 : Maue-Dikson W, Trefl er M, Dikson DR. Comparison of dosimetry and image quality in omputed and onventional tomography. Radiology 1979;131 : Rowe LD, Miller E, rant-zawadzki M. Computed tomography in maxillofaial trauma. Laryngosope 1981 ;91 : Christensen EE, Curry III TS, Nunnally J. n introdution to th e physis of diagnosti radiology. Phi ladelphia: Lea & Febiger, 1973 : Pentl ow KS. Dosimetry in omputed tomog raphy. In: Newton GH, Potts DG, eds. Radiology of the skull and brain: tehnial aspets of omputed tomography. SI. Loui s: Mosby, 1981 : Hesselink JR, New PFJ, Davis KR, et al. Computed tomography of the paranasal sinuses and fae: II. Pathologial anatomy. J Comput ssist Tomogr 1978;2 :

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