HEAD AND NECK RADIOLOGY

Sino-orbital osteoma with osteoblastoma-like features:case reports

Zeynep Yazici & Bulent Yazici & Ulviye Yalcinkaya &

Gokhan Gokalp

Received: 18 July 2011 /Accepted: 17 October 2011 /Published online: 15 November 2011# Springer-Verlag 2011

Abstract Most of the orbital osteomas arise from theadjacent paranasal sinuses. Some of them may containosteoblastoma-like areas and may be misdiagnosed asosteoblastoma, both radiologically as well as histopatholog-ically. Sino-orbital osteomas with osteoblastoma-like featuresshow a typical radiological appearance. They have a distinctzonal pattern, in which less dense osteoblastoma-like areas arelocated at the base of the lesion and dense mature bone islocated at the periphery. These broad-based bone lesions alsohave a tendency for extracavitary polypoid growths from theparanasal sinus into the adjacent orbit. We report here the CTand MR imaging findings of three cases with sino-orbitalosteoma with osteoblastoma-like features.

Keywords Orbit . Osteoma . Osteoblastoma . Computedtomography .Magnetic resonance imaging

Introduction

Osteomas are benign, slowly growing, bone-forming neo-plasms. In the craniofacial region, they are most common in

the paranasal sinuses and usually asymptomatic until theyextend out of the sinus and/or obstruct the sinus drainage.Most of the orbital osteomas arise from the adjacent paranasalsinuses. Although asymptomatic, small paranasal sinusosteomas are relatively common; sino-orbital osteomas arerare and have been published in a few reports [1–3].

These tumors are histologically divided into ivory,mature, and mixed types depending on the proportions ofdense lamellar bone and fibrous stroma; some osteomasmay contain the osteoblastoma-like areas [4, 5]. Osteomaswith osteoblastoma-like features may have a differentradiographic appearance from that of other osteomas andmay be misinterpreted as osteoblastomas. Such a misdiag-nosis may mislead the bone pathologist who requires closecollaboration with the radiologist in order to arrive atdiagnostic impressions, and as a result of this, someosteomas may be reported both radiologically and histo-pathologically as osteoblastoma [4].

Here, we present the imaging findings of three caseswith sino-orbital osteoma with osteoblastoma-like features.As far as we know, there is no report describing the CT andMR imaging features of sino-orbital osteomas withosteoblastoma-like features in the radiologic literature.

Case reports

Case 1

A 12-year-old boy was admitted with diplopia for 3 weeks. Hehad slight pain around the right orbit. There were proptosis,inferior globe displacement, and restriction of upward gaze onthe same side, without visual deficit. The CT scan demon-strated a bone mass measured 20×26×19 mm in size(Fig. 1a). The mass originated from the ethmoidal sinus

Z. Yazici (*) :G. GokalpDepartment of Radiology, Medical Faculty, Uludag University,Gorukle Campus,Bursa 16059, Turkeye-mail: zyazici@uludag.edu.tr

B. YaziciDepartment of Ophthalmology, Medical Faculty,Uludag University,Bursa, Turkey

U. YalcinkayaDepartment of Pathology, Medical Faculty, Uludag University,Bursa, Turkey

Neuroradiology (2012) 54:765–769DOI 10.1007/s00234-011-0973-9

and extended into the orbit and frontal sinus in a polypoidfashion. It displayed a cauliflower-like growth without bonedestruction. The inner part of the mass had a ground-glassappearance, and the outer part was like compact bone. OnMRI, both T1- and T2-weighted images showed signal voidof the densely osseous portion of the mass, which also didnot enhance after contrast agent administration (Fig. 1b–d).The portion of the mass with ground-glass appearance on CTdemonstrated low signal intensity on both T1- and T2-weighted images and was enhanced slightly on post-contrastimages. The mass was completely removed via medialorbitotomy. Histopathologically, the lesion showedosteoblastoma-like areas, which were composed of anasto-mosing trabeculae of woven bone rimmed by osteoblasts andosteoclasts (Fig. 2). The interosseous stroma was loosely

textured and composed of fibroblasts and numerous thin-walled, often ectatic, vessels. Dense mature bone wasobserved at the lesion periphery. These histopathologicalfindings together with those of imaging led to the diagnosisof osteoma with osteoblastoma-like features. In a follow-upperiod of 14 months, clinical and radiological examinationsrevealed no recurrent disease.

Case 2

A 15-year-old boy presented with right orbital pain for2 months. The clinical findings included proptosis, lateraldisplacement of the globe, and restriction of inward gaze.The CT scan revealed a fronto-ethmoidal mass measuring30×28×28 mm (Fig. 3). This broad-based, cauliflower-like

Fig. 1 Case 1. a Axial CT scanshows a cauliflower-like bonemass of the paranasal sinusextending into the right orbitalcavity. The inner part withground-glass appearance of themass is sharply demarcated fromthe outer part of dense bone.Fat-suppressed T2-weightedaxial (b) and non fat-suppressedT1-weighted coronal (c) MRimages show dark signal inten-sity of the densely osseous por-tion of the mass. The portion ofthe mass with ground-glassappearance on CT demonstrateslow signal intensity on bothimages. d Enhanced T1-weighted coronal MR imagereveals the enhancement of theinner part of the mass

Fig. 2 Photomicrographs of the histologic specimen of case 1(hematoxylin & eosin, ×100). a Osteoblastoma-like area of the lesiondemonstrating the interanastomosing trabeculae of woven bonerimmed by osteoblasts (arrow) and osteoclasts (arrowhead). The

interosseous stroma contains fibroblasts and thin-walled vascularchannels. b Mature cortical bone component of the lesion. c Theimage shows the transition of osteoblastoma-like area (black asterisk)to mature cortical bone (white asterisk)

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mass originated from the frontal sinus and had a centrifugalextension into the adjacent orbit and ethmoidal sinus. Nobone destruction was evident. Of the mass, the innerportion had ground-glass density, and the outer portionhad compact bone density. The patient had no MR imaging.The mass was completely removed through orbitotomy.Histopathological examination revealed dense mature bonewith osteoblastoma-like areas, which was consistent withosteoma with osteoblastoma-like features. The patient hasbeen followed up for 26 months. Clinical and radiologicalexaminations showed no recurrent disease.

Case 3

A 26-year-old man presented with proptosis and slight painin the right eye for 3 months. There was restriction oflateral gaze without visual deficit. The CT scan demon-strated a bone mass measuring 28×24×28 mm arising fromthe ethmoidal sinus (Fig. 4). The mass had a cauliflower-like appearance with exophytic growth into the orbit andslightly into the frontal sinus. The density of the mass wasground-glass-like at the base and compact bone-like at theperiphery. No bone destruction was seen. The portion of themass with ground-glass appearance on CT showed lowsignal intensity on both T1- and T2-weighted MR images

and homogeneous enhancement on post-contrast images(Fig. 5). The dense osseous area was signal void on all MRimages. Histopathological diagnosis of the mass that wascompletely removed through orbitotomy was osteoma withosteoblastoma-like features. After a 12-month follow-up,the lesion did not recur clinically or radiologically.

Discussion

The radiographic appearance of the ivory osteoma, which isthe classical type of the osteomas, is similar to lesionscomposed of predominantly very dense bone with onlysmall lucent areas at most [4]. In the mature-type osteomas,less dense areas with appearance similar to that of thefibrous matrix are seen adjacent to the areas of very densebone. Some osteomas can contain large osteoblastoma-likeareas, and these lesions have been designated as osteomaswith osteoblastoma-like features because of their differenthistological and radiological characteristics [5].

In their descriptive study, McHugh et al. histologicallyreviewed 45 paranasal sinus osteomas from a period of22 years and observed osteoblastoma-like areas in 17 (38%)of the cases [4]. Only 12 of 45 lesions involved the orbit,and seven of these sino-orbital lesions had osteoblastoma-

Fig. 3 Case 2. Axial (a) andcoronal (obtained in prone posi-tion) (b) CT scans show a bonemass originating from the rightfrontal sinus and extending tothe right orbital cavity andethmoidal sinus. The inner por-tion of the mass has ground-glass density and the outer por-tion, a compact bone density

Fig. 4 Case 3. Axial (a), coronal (b), and sagittal (c) CT scans show abroad-based bony mass arising from the ethmoidal sinus andextending into the right orbit. The portion of the mass with ground-

glass appearance is located at the attachment site to the bone of originand those with compact bone density, at the periphery of the mass

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like areas. Microscopically, the osteoblastoma-like areas arecomposed of interanastomosing woven bone trabeculaelined by osteoblasts and osteoclasts and associated with aninterosseous fibrous stroma containing numerous smallvessels.

Osteoblastoma-like areas typically are located at thetumor base, i.e., at the site of attachment to the bone oforigin, and surrounded partially by a peripheral densemature bone [4]. The radiologic appearance of the lesioncorrelates well with the histological features. On CT scans,osteoblastoma-like areas appear as ground-glass areas andperipheral zones as compact cortical bone. Peripheral densebone is signal void, and the osteoblastoma-like area ishypointense on both T1- and T2-weighted MR images.Osteoblastoma-like areas homogeneously enhance aftercontrast media administration. The lesion has acauliflower-like appearance with exophytic growth fromthe paranasal sinuses into the adjacent orbit.

We think that CT images better delineate the true natureof the lesion than MR images. On MR images, the signalvoid peripheral zone of the lesion may not be distinguishedfrom the air within the paranasal sinuses and can causeconfusion in diagnosis without corresponding CT images.

In McHugh et al.'s series, 62% of paranasal sinusosteomas arose in the frontal sinus and 24% in the ethmoidsinus [4]. The patient ages range from 12 to 70 years(median age, 37 years). Similar to the study population

overall, tumors with osteoblastoma-like features occurredmost frequently in the frontal and ethmoid sinuses (59%and 44%, respectively) with a similar median age.

Osteoblastomas are less common than osteomas in thecraniofacial region and very rarely affect the orbit. Theyfrequently occur in the mandible and maxilla [6, 7].Radiographically, osteoblastomas usually appear as a mixedlytic and blastic mass; the intra-lesional mineralization maybe minimal or extensive, but is greatest centrally [6]. Mostosteoblastomas have a peripheral rind of sclerotic bone [6,7]. These tumors usually produce bone remodeling andexpansion of the host bone. However, osteomas withosteoblastoma-like features have heavily ossified areasand tend to form cauliflower-like extracavitary growth.There are about 25 published cases of primary osteoblas-toma of paranasal sinuses in the literature [4, 8, 9]. Asstated by McHugh et al., some of them may actuallyrepresent osteomas with osteoblastoma-like features basedon their radiographic illustrations [8, 9].

Fibrous dysplasia and ossifying fibroma can be includedin the radiological differential diagnosis of osteoma withosteoblastoma-like features. Both lesions are expansiletumors. The density of the fibrous dysplasia is determinedby the proportion of mineralized to fibrous tissue andusually shows homogeneous ground-glass appearance. Thecharacteristic CT appearance of the ossifying fibroma is awell-defined mass with a thin sclerotic margin. In the center

Fig. 5 MR images of case 3.On T1-weighted (a) and T2-weighted axial (b) and T1-weighted coronal (c) MRimages, the portion of the masswith ground-glass appearanceon CT shows low signal inten-sity and the dense osseous por-tion, dark signal intensity. dEnhanced T1-weighted coronalMR image reveals enhancementof the inner portion of the mass

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of the lesion, there is often a patchy pattern of osteoblasticand osteolytic areas.

Osteoid osteoma histopathologically cannot be distin-guished from osteoblastoma. The main differential diag-nostic criterion of osteoid osteoma with osteoblastoma isthe size of the lesion. Lesions greater than 2 cm areclassified as osteoblastoma. Osteoid osteomas of thecraniofacial bones are exceptionally uncommon [6]. Theirclassic radiological presentation is a lucent nidus surroundedby a zone of reactive sclerosis. They do not show polypoidextracavitary growths. Furthermore, osteoid osteomas arecharacterized with a distinctive pain pattern.

Osteomas extending into the orbit can cause symptomssuch as globe displacement, restriction of eye movement,visual changes, pain, and ptosis. McHugh et al. reportedthat, as compared with the other types of osteomas,osteomas with osteoblastoma-like features caused visualsymptoms more often, and the duration of symptoms priorto presentation was slightly shorter [4]. Regarding size,osteomas with osteoblastoma-like features tended to beslightly larger than those without. The authors noted thatosteomas with osteoblastoma-like features were three timesmore common in men than the other osteomas, whichoccurred equally in both sexes. The median age was similarbetween the two groups (37 versus 39 years) [4]. Our threepatients were also men, and their ages were 12, 15, and26 years.

If they are symptomatic, osteomas are treated with surgicalexcision. In our cases, the lesions were removed viaorbitotomy. A cleavage plane between the lesion and thenormal bone can be achieved by striking on its parts adjacentto the bone with hammer and chisel. Following this procedure,if the tumor is too large to be removed from the surgicalopening, it can be drilled into pieces. We did not observe anyresidual tumor or recurrence in our three cases after surgeryduring mean 17-month follow-up period. In McHugh et al.'sseries, osteomas with osteoblastoma-like features were more

often incompletely excised; conversely, clinical recurrenceswere less common [4].

In conclusion, osteoma with osteoblastoma-like featuresmay not be distinguished histopathologically from osteo-blastoma in the absence of radiographic correlation. Thedistinctive radiological features of the osteoma withosteoblastoma-like features are the distinct zonal pattern,in which less dense osteoblastoma-like areas are locatedat the base of the lesion and dense mature bone is locatedat the periphery, and the tendency for extracavitarypolypoid growths.

Conflict of interest We declare that we have no conflict of interest.

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