Clinical Radiology (! 992) 46, 237-242
Imaging of Orbitofrontal Cholesterol Granuloma C. A. R O W L A N D H I L L and I. F. M O S E L E Y
Department of Radiology, Moorfields Eye Hospital, London The radiological findings in 31 patients with a histologically proven orbitofrontal cholesterol granuloma are presented. Plain films and computed tomography (CT) both show a characteristic lytic lesion allowing a reasonably confident diagnosis to be made preoperatively, thus facilitating appropriate surgery. The most important differential diagnoses on clinicoradiological grounds are lacrimal gland carcinoma and dermoid cyst. On plain films cholesterol granulomas typically show constancy of site, lysis of the superior orbital margin, frequent extension into the frontozygomatic process and absent or minimal surrounding sclerosis. On CT ragged bone destruction with a soft tissue mass no denser than brain extending extraperiosteally into the orbit are the most typical features. MRI and other imaging modalities are discussed. Rowland Hill, C.A. & Moseley, I.F. (1992). Clinical Radiology 46, 237-242. Imaging of Orbitofrontal Cholesterol G r a n u l o m a
Accepted for Publication 14 May 1992
Cholesterol granulomas are osteolytic lesions characterized by granutomatous infiltration surrounding cholesterol crystals. They have been described in numerous sites in the skull and facial skeleton including the frontal and petrous temporal bones, maxilla and zygoma. Frontal bone lesions are relatively uncommon but occur in a particular, characteristic site immediately adjacent to the lacrimal fossa [1,2]. The plain film and computed tomography findings in 31 patients are described in detail. The radiology of some of the patients included in this series has been previously described [1], as have the clinical features [2].
P A T I E N T S AND M E T H O D S Over the period from 1974 to 1991, 31 patients who proved to have orbitofrontal cholesterol granuloma were referred to Moorfields Eye Hospital. O f these 20 had plain skull radiographs or t o m o g r a m s available for review, 21 had computed t o m o g r a p h y (CT) studies of adequate quality for inclusion and one was studied by magnetic resonance imaging (MRI). Plain film series typically comprised occipitofrontal, occipitomental and lateral projections and in some cases optic canal views were also available. Patients undergoing CT were examined on a wide variety of scanners. Sixteen of the patients had axial and coronal images: in 14 patients the latter were direct coronal images but in two cases the coronal images were reformatted. Fourteen examinations comprised contiguous 4 m m or 5 m m slices but seven included 2 m m or 1.5 m m sections. Twelve patients were studied only without contrast medium, three only after and six before and after intravenous injection. The single patient studied by M R I had Tl-weighted inversion recovery and T2-weighted spin echo sequences performed on a 0.3T Picker M R imager.
Correspondence to: Dr 1. F. Moseley, Department of Radiology, Moorfields Eye Hospital, City Road, London EC1V 2PD.
RESULTS Of the 31 patients, 28 were male; mean age at presentation was 43 years, range 25-68. The mean age of the three women was 44 years, range 40-50. A clear history of blunt trauma to the affected orbit was given by seven patients (23%). This occurred between 3 years and 1 month prior to the onset of symptoms. The commonest presenting symptom was proptosis which was described by 16 patients (58%). Other symptoms included diplopia, mild visual blurring, a dull ache and swelling or drooping of the upper eyelid. On examination all but one patient had measurable proptosis and in the majority there was a palpable mass in the upper temporal quadrant of the orbit.
Plain Films The 20 cases reviewed showed characteristic appearances (Fig. 1). All lesions were in the frontotemporal margin of the orbit, 10 on the right and 10 on the left. The maximum diameter of the lesion on the posteroanterior view ranged from 1.5 to 3.75 cm (mean 2.55 cm). All
Fig. 1 -Plain radiograph of a right sided orbitofrontal cholesterol granuloma. There is a well defined osteolytic lesion without surrounding sclerosis. The lucency extends into the zygomatic process of the frontal bone (arrow) as far as the frontozygomatic synostosis.
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(a)
minimal or no sclerosis and was either smooth and regular (10 cases) or slightly irregular (10 cases). In 16 cases there was clear extension into the zygomatic process of the frontal bone and in at least six of these extension to but never beyond the frontozygomatic synostosis. In eight patients the granuloma abutted the lateral margin of the ipsilateral frontal sinus and in two it appeared to extend into the sinus; both these lesions were more than 3 cm in transverse diameter. In no case were fragments or spicules of bone visible on the plain films. Two patients had postoperative plain films (Fig. 2). In one the residual abnormality was moderate sclerosis at the site of the excised lesion with no evidence of the previous erosion, while in the other a persistent 1.75 cm lucency with a 2 m m sclerotic border was seen; the defect in the superior orbital margin had decreased from 2.5 cm to 0.75 cm in diameter.
Computed Tomography
(b)
(c)
(d) Fig. 2 Two examples of plain film changes following surgery: Right sided lytic lesion (a) abutting and possibly extending into the frontal sinus (arrow). The lateral part of the superior orbital rim is eroded; (b) the same patient 1 year later after surgery. The lucency has been replaced by ill-defined sclerosis and the superior orbital rim has been restored. A left sided lesion (c) before and (d) 6 months after surgery. The lucent area has become smaller and there is partial restoration of the superior orbital margin. Note extension into the zygomatic process on the preoperative film.
consisted of a lucent defect with lysis of the superior orbital margin except in one case where the margin was thinned but intact. The lesions were well defined, except in three cases where the medial border abutting the frontal sinus was less clear cut. In all cases the margin showed
O f the 21 cases examined 13 were on the left and eight on the right. Where measurements could be made the maximum diameter of the lesion ranged from 2.25 to 3.2 cm (mean 2.8 cm). In 14 cases there was clear expansion of the dipl6e and in all cases there was bone destruction involving at least the orbital roof with a ragged outline to the surrounding bone (Fig. 3). In 11 patients there was apparent spiculation or fragmentation of bone suggesting an aggressive or neoplastic lesion (Fig. 4). Intraosseous extension to the frontozygomatic synostosis occurred in six cases but in some of the patients this was difficult to assess on the images available. It m a y have been much more frequent. In no case, however, did the synostosis appear to be transgressed. In seven patients the lesion reached the lateral margin of the ipsilateral frontal sinus and in two of these it extended into the sinus. Extraosseous spread into the orbit occurred in all cases and in all but two the intraorbital component of the lesion appeared at least as large as the intraosseous component. The lesion spread superiorly into the anterior cranial fossa in 10 cases and laterally into the temporal fossa in six (Fig. 5). In all but one case the globe was deviated inferiorly by the mass and proptosis was evident in 19. Medial (five cases) and lateral deviation (two cases) was less common and never marked. Slight flattening of the superior aspect of the globe was seen in 16 patients. In 15 patients the mass could be seen extending posterior to the globe. In most patients the lacrimal gland could not be distinguished on CT from the granuloma. There was often no plane of definition from the superior or lateral rectus muscles but the lesion always remained extraconal. The attenuation of the lesions was homogenous and approximately isodense with brain in all but two patients, in whom it was hypodense with no change after contrast enhancement. Measurements made in three patients showed the attenuation of the granuloma to range from 36 to 40 Hounsfield Units. There were no hyperdense lesions.
Magnetic Resonance The lesion showed strikingly higher signal than that of the intraorbital fat on both Tl-weighted inversion recovery and T2-weighted spin echo sequences (Fig. 6). The patient was also examined by CT and although the lesion
239
ORBITOFRONTAL CHOLESTEROL GRANULOMAS
(a)
(b)
(c) Fig. 3 - Three different cases showing typical CT features of cholesterol granuloma. (a) Direct coronal CT scan of the orbits showing an isointense (relative to brain) soft tissue mass markedly expanding the dip16e. The bony margins are very ragged and irregular in contrast to the plain film appearances of the same lesion (Fig. 1). The floor of the anterior cranial fossa is partially eroded (arrow). (b) Direct coronal CT showing marked inferior deviation of the globe by an intradipl6ic soft tissue mass which has extended into the orbit. There is extension into the zygomatic process (arrow). (c) Direct axial CT showing an isointense mass in the superotemporal quadrant of the orbit. The lateral bony margin of the lesion is irregular. The globe is displaced inferiorly.
was more readily apparent on MRI no useful additional information was gained from the M R study. In cases where full documentation was available for review, the correct diagnosis was made or thought to be the likeliest differential preoperatively in 60% of cases on the basis of clinical and radiological findings. The main alternative diagnosis was a dermoid cyst. DISCUSSION Orbitofrontal cholesterol granuloma is an uncommon lesion of unknown aetiology. On average over the last 17 years, 1.8 cases per year have been seen at this institution. This compares with approximately 2.5 cases per year of lacrimal gland carcinoma and 3.75 cases of pleomorphic adenoma of the lacrimal gland. Various terms have been used to describe cholesterol granuloma, including lipid granuloma, cholesteatoma, xanthomatosis, histiocytic granuloma, haematoma and chronic haematic cyst. These terms are either misleading or inaccurate and cholesterol granuloma is preferred. Histological appearances are highly specific, with cho-
lesterol clefts surrounded by foreign-body giant cells (Fig. 7). A crucial distinguishing feature from a dermoid is the absence of epithelial elements [3], which may explain why cholesterol granulomas so rarely recur after surgery. Earlier theories of the pathogenesis of cholesterol granuloma included a localized xanthomatosis and a histiocytosis X variant [4-6]. Cholesterol granulomas of the petrous bone have been studied more extensively and are thought to be related to impaired ventilation of aerated cavities resulting in mucosal oedema and haemorrhage [7,8]. Degradation of erythrocyte membranes results in deposition of cholesterol which subsequently crystallizes; the crystals then stimulate a granulomatous reaction. Clearly the initiating factors must be different in the lesions originating in nonpneumatized frontal bone. However, evidence of haemorrhage was present at surgery in all the cases described by McNab and Wright [2] whose composition overlaps with the present series, although the exact cause of haemorrhage is unclear. The frequency of a definite history of trauma is very variable, ranging from none of eleven cases [9], to up to one third of cases [2,3,10]. It is possible that the trauma may be mild and perhaps forgotten; the strong male preponderance in
240
CLINICAL RADIOLOGY
(a)
(b) Fig. 4 (a) Direct axial and (b) reformatted coronal CT showing fragments of bone around the periphery of the lesion. There is extensive destruction of the orbital roof with extension extradurally into the anterior cranial fossa.
Fig. 5 Direct coronal CT showing irregular erosion of the lateral orbital wall with extension into the temporal fossa. The lesion has also involved the lateral wall of the frontal sinus although the sinus remains fully aerated.
these and other reports and the high incidence of heavy manual occupations may reflect a traumatic aetiology. It has also been suggested that a dipl6ic anomaly may predispose to haemorrhage [3]. Cholesterol granulomas most commonly present with proptosis. Pain is not a marked feature but some patients complain o f a dull ache. Diplopia and blurred vision also occur. Surgical treatment involves aspiration of contents and stripping or curettage of the lining which is highly successful. One case in the current series recurred 2 years
after surgery and only one other possible recurrence has been reported in the literature [2,11]. Our series demonstrates that cholesterol granulomas have characteristic appearances on both plain radiographs and CT. The typical plain film appearance is of a well defined superotemporal osteolytic lesion with minimal or no surrounding sclerosis and a smooth or only slightly irregular border. Extension into the zygomatic process, as described by Lloyd [1] is frequent. At CT an isodense or hypodense, expanding lytic lesion produces ragged bone destruction and invariably extends extraperiosteally into the orbit, causing proptosis and inferior deviation of the globe in almost all cases. Extension into the anterior cranial and temporal fossae occurs less frequently. Bone spiculation or fragmentation may be seen in 50% of cases. The absence of this latter feature on plain films presumably reflects the superior contrast resolution of CT. Very similar appearances were described in a recent CT study of 11 patients in Holland [9] and in other reports [3,12,13]. Although in our series contrast enhancement was not observed in the five patients studied before and after contrast medium, enhancement has been reported in a single case [3]. Radiological differential diagnosis of a lytic lesion in the frontotemporal orbital margin includes lacrimal gland neoplasm, metastasis, dermoid or epidermoid cyst, aneurysmal bone cyst [14], eosinophilic granuloma [15], cystic ossifying fibroma, intradipl6ic meningioma [16], frontal sinus mucocoele and hydatid cyst. Carcinomas of the lacrimal gland, which together with dermoids repre-
241
ORBITOFRONTAL CHOLESTEROL GRANULOMAS
(~)
(a)
(b) Fig. 6 (a) Tl-weighted inversion recovery (TR 2100 ms, TI 500 ms) coronal MRI scan showing a markedly hyperintense mass in the superotemporal orbit which has eroded through the vault into the anterior cranial fossa and is displacing the frontal lobe. (b) T2-weighted •spin echo (TR 2000 ms, TE 80 ms) axial MRI showing signal hyperintensity.
sent the main differential diagnostic consideration on clinicoradiological grounds, but whose treatment is radically different, also cause irregular bone destruction with or without sclerosis. They may be denser than brain on CT, approximately one third containing calcification [17] and enhance with intravenous contrast medium. Dermoid cysts usually have a sclerotic border and do not extend into the zygomatic process [1]. On CT they may show a characteristic bony defect in the lateral orbital wall and two-thirds contain areas of low attenuation. Benign lacrimal gland tumours cause local pressure erosion with expansion of the lacrimal fossa. Cystic ossifying fibroma and eosinophilic granuloma characteristically have sclerotic margins. We encountered a frontal mucocoele which had several features suggestive of cholesterol granuloma except that it was hyperdense relative to brain, a feature not seen in any of the cholesterol granulomas in this or other reported series (Fig. 8). The single lesion studied by MRI showed a higher signal than intraorbital fat not only on T2 weighting but also on a heavily Tl-weighted inversion recovery sequence, reflecting the paramagnetic effects of haemoglobin degradation products. Similar appearances are reported by Fukuta and Jackson [13] in an orbital lesion and in studies of petrous bone lesions [18,19]. In one case [18] appearances were unchanged after intravenous gadolinium-DTPA. Few other lesions in the orbitofrontal region show similar M R characteristics; dermoid cysts may appear similar but more commonly give low signal on T1 weighting. However CT and plain
(b) Fig. 7 Photomicrographs of the wall of a cholesterol granuloma showing the characteristic arrangement of cholesterol clefts surrounded by a chronic inflammatory infiltrate including occasional giant cells. (Original magnification (a) x 100, (b) x 250.)
Fig. 8 Enhanced axial CT scan of a mucocoele extending into the orbit. It is hyperdense with respect to normal brain.
film appearances in combination could be expected to distinguish these entities. Cholesterol granulomas may be diagnosed with reasonable confidence on the basis of clinical and radiological data. Plain skull radiography shows a characteristic appearance with a very limited differential diagnosis. CT
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also has typical appearances and enables the surgeon to assess intraosseous and extraosseous spread preoperatively. Since surgery for lacrimal gland carcinoma is much more radical, awareness of the possibility of this benign lesion is very important, particularly as the initial impression of the CT appearance may be of an aggressive bonedestroying tumour. CT may also be helpful in assessing the other main differential diagnosis, a dermoid cyst. A role for three-dimensional CT for pre-surgical planning has been proposed [13] but this facility is not freely available. Limited experience with MRI shows that the lesion is well demonstrated but a role for M R I in management of these lesions is yet to be established; when the diagnosis is in doubt, however, the characteristic signal changes can be helpful. MRI would also be expected to delineate intracranial extension better than CT as well as defining intraorbital anatomy more clearly. The angiographic and radionuclide bone scan appearances of cholesterol granuloma have been reported [20,21] but are no longer likely to be of clinical relevance. Acknowledgements. We are grateful to Professor Alec Garner for providing Fig. 7 and to Mr John Wright whose patients comprise this series.
6 Nichols JVV. Cholesterol containing granuloma of the orbital wall. American-Journal of Ophthalmology 1956;41:234 247. 7 Beaumont GD. The effects of exclusion of air from pneumatised bones. Journal of Laryngology and Otology 1966;80:236 249. 8 Nager GT, Vanderveen TS. Cholesterol granuloma involving the temporal bone. Annals of Otology 1976;85:204-209. 9 Eijpe AA, Koornneef L, Verbeeten B Jr, Peeters FLM, Zonnefeld FW. Cholesterol granuloma of the frontal bone: CT diagnosis. Journal of Computer Assisted Tomography 1990; 14:914-917. 10 Ramsey GS, Laws HW, Pritchard JE, Elliot H. Post-traumatic granuloma of the bony orbit simulating tumour. Journal of the Canadian Medical Association 1948;59:206-211. 11 Pfeiffer RL, Nicholl RJ. Dermoids and epidermoids of the orbit.
Transactions 12
13 14 15
16 t7 18
REFERENCES 1 Lloyd GAS. Cholesterol granutoma of the facial skeleton. British Journal of Radiology 1986;59:481-485. 2 McNab AA, Wright JE. Orbitofrontal cholesterol granuloma. Ophthalmology 1990;97:28 32. 3 Parke DW, Font RL, Boniuk M, McCrary JA. 'Cholesteatoma' of the orbit. Archives of Ophthalmology 1982;100:612 616. 4 Knapp A. Xanthomatosis of the orbit: report of two cases. Archives of Ophthalmology 1934;11:141-147. 5 Hanbery JW, Rayport M. Unilateral exophthalmos due to orbitofrontal cholesterol granuloma. American Journal of Surgery 1955;89:1144 1162.
19 20
of
the
American Ophthalmological Society
1948;46:218-243. Elmaleh C, D'Hermies D, Barraco P, Pouliquen Y. Le choleste~itome de l'orbite: une etiologic rare de tumeur orbitaire. Journal Fran¢ais d'Ophtalmologie 1989;12:139 142. Fukuta K, Jackson IT. Epidermoid cyst and cholesterol granuloma of the orbit. British Journal of Plastic Surgery 1990;43:521-527. Johnson TE, Bergin DJ, McCord CD. Aneurysmal bone cyst of the orbit. Ophthalmology 1988;95:86 89. Jakobiec FA0 Trokel SL, Aron-Rosa D, Iwamoto T, Doyon D. Localised eosinophilic granuloma (Langerhans' cell histiocytosis) of the orbital frontal bone. Archives of Ophthalmology 1988;98:1814 1820. Halpin SFS, Britton JA, Wilkins P, Uttley D. Intradipl6ic meningioma: CT and MR appearance. Neuroradiology 1991;33:247-250. Lloyd GAS. Lacrimal gland tumours: the role of CT and conventional radiology. British Journal of Radiology 1981;54:1034-1038. Martin N, Sterkers O, Mompoint D, Julien N, Nahum H. Cholesterol granulomas of the middle ear cavities: MR imaging. Radiology 1989;172:521-525. Clifton AG, Phelps PD, Brookes GB. Cholesterol granuloma of the petrous apex. British Journal of Radiology 1990;63:724 726. Wright JE. Lipid containing granuloma of the frontal bone.
Transactions of the Ophthalmological Societies of the UK 1970;90:295 298. 21 Eugenidis N, Gessaga E, Chrzanowski R. Bone scan and angiography for orbitofrontal cholesterol granuloma. Neuroradiology 1980;19:93-94.
Imaging of Orbitofrontal Cholesterol Granuloma C. A. R O W L A N D H I L L and I. F. M O S E L E Y
Department of Radiology, Moorfields Eye Hospital, London The radiological findings in 31 patients with a histologically proven orbitofrontal cholesterol granuloma are presented. Plain films and computed tomography (CT) both show a characteristic lytic lesion allowing a reasonably confident diagnosis to be made preoperatively, thus facilitating appropriate surgery. The most important differential diagnoses on clinicoradiological grounds are lacrimal gland carcinoma and dermoid cyst. On plain films cholesterol granulomas typically show constancy of site, lysis of the superior orbital margin, frequent extension into the frontozygomatic process and absent or minimal surrounding sclerosis. On CT ragged bone destruction with a soft tissue mass no denser than brain extending extraperiosteally into the orbit are the most typical features. MRI and other imaging modalities are discussed. Rowland Hill, C.A. & Moseley, I.F. (1992). Clinical Radiology 46, 237-242. Imaging of Orbitofrontal Cholesterol G r a n u l o m a
Accepted for Publication 14 May 1992
Cholesterol granulomas are osteolytic lesions characterized by granutomatous infiltration surrounding cholesterol crystals. They have been described in numerous sites in the skull and facial skeleton including the frontal and petrous temporal bones, maxilla and zygoma. Frontal bone lesions are relatively uncommon but occur in a particular, characteristic site immediately adjacent to the lacrimal fossa [1,2]. The plain film and computed tomography findings in 31 patients are described in detail. The radiology of some of the patients included in this series has been previously described [1], as have the clinical features [2].
P A T I E N T S AND M E T H O D S Over the period from 1974 to 1991, 31 patients who proved to have orbitofrontal cholesterol granuloma were referred to Moorfields Eye Hospital. O f these 20 had plain skull radiographs or t o m o g r a m s available for review, 21 had computed t o m o g r a p h y (CT) studies of adequate quality for inclusion and one was studied by magnetic resonance imaging (MRI). Plain film series typically comprised occipitofrontal, occipitomental and lateral projections and in some cases optic canal views were also available. Patients undergoing CT were examined on a wide variety of scanners. Sixteen of the patients had axial and coronal images: in 14 patients the latter were direct coronal images but in two cases the coronal images were reformatted. Fourteen examinations comprised contiguous 4 m m or 5 m m slices but seven included 2 m m or 1.5 m m sections. Twelve patients were studied only without contrast medium, three only after and six before and after intravenous injection. The single patient studied by M R I had Tl-weighted inversion recovery and T2-weighted spin echo sequences performed on a 0.3T Picker M R imager.
Correspondence to: Dr 1. F. Moseley, Department of Radiology, Moorfields Eye Hospital, City Road, London EC1V 2PD.
RESULTS Of the 31 patients, 28 were male; mean age at presentation was 43 years, range 25-68. The mean age of the three women was 44 years, range 40-50. A clear history of blunt trauma to the affected orbit was given by seven patients (23%). This occurred between 3 years and 1 month prior to the onset of symptoms. The commonest presenting symptom was proptosis which was described by 16 patients (58%). Other symptoms included diplopia, mild visual blurring, a dull ache and swelling or drooping of the upper eyelid. On examination all but one patient had measurable proptosis and in the majority there was a palpable mass in the upper temporal quadrant of the orbit.
Plain Films The 20 cases reviewed showed characteristic appearances (Fig. 1). All lesions were in the frontotemporal margin of the orbit, 10 on the right and 10 on the left. The maximum diameter of the lesion on the posteroanterior view ranged from 1.5 to 3.75 cm (mean 2.55 cm). All
Fig. 1 -Plain radiograph of a right sided orbitofrontal cholesterol granuloma. There is a well defined osteolytic lesion without surrounding sclerosis. The lucency extends into the zygomatic process of the frontal bone (arrow) as far as the frontozygomatic synostosis.
238
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(a)
minimal or no sclerosis and was either smooth and regular (10 cases) or slightly irregular (10 cases). In 16 cases there was clear extension into the zygomatic process of the frontal bone and in at least six of these extension to but never beyond the frontozygomatic synostosis. In eight patients the granuloma abutted the lateral margin of the ipsilateral frontal sinus and in two it appeared to extend into the sinus; both these lesions were more than 3 cm in transverse diameter. In no case were fragments or spicules of bone visible on the plain films. Two patients had postoperative plain films (Fig. 2). In one the residual abnormality was moderate sclerosis at the site of the excised lesion with no evidence of the previous erosion, while in the other a persistent 1.75 cm lucency with a 2 m m sclerotic border was seen; the defect in the superior orbital margin had decreased from 2.5 cm to 0.75 cm in diameter.
Computed Tomography
(b)
(c)
(d) Fig. 2 Two examples of plain film changes following surgery: Right sided lytic lesion (a) abutting and possibly extending into the frontal sinus (arrow). The lateral part of the superior orbital rim is eroded; (b) the same patient 1 year later after surgery. The lucency has been replaced by ill-defined sclerosis and the superior orbital rim has been restored. A left sided lesion (c) before and (d) 6 months after surgery. The lucent area has become smaller and there is partial restoration of the superior orbital margin. Note extension into the zygomatic process on the preoperative film.
consisted of a lucent defect with lysis of the superior orbital margin except in one case where the margin was thinned but intact. The lesions were well defined, except in three cases where the medial border abutting the frontal sinus was less clear cut. In all cases the margin showed
O f the 21 cases examined 13 were on the left and eight on the right. Where measurements could be made the maximum diameter of the lesion ranged from 2.25 to 3.2 cm (mean 2.8 cm). In 14 cases there was clear expansion of the dipl6e and in all cases there was bone destruction involving at least the orbital roof with a ragged outline to the surrounding bone (Fig. 3). In 11 patients there was apparent spiculation or fragmentation of bone suggesting an aggressive or neoplastic lesion (Fig. 4). Intraosseous extension to the frontozygomatic synostosis occurred in six cases but in some of the patients this was difficult to assess on the images available. It m a y have been much more frequent. In no case, however, did the synostosis appear to be transgressed. In seven patients the lesion reached the lateral margin of the ipsilateral frontal sinus and in two of these it extended into the sinus. Extraosseous spread into the orbit occurred in all cases and in all but two the intraorbital component of the lesion appeared at least as large as the intraosseous component. The lesion spread superiorly into the anterior cranial fossa in 10 cases and laterally into the temporal fossa in six (Fig. 5). In all but one case the globe was deviated inferiorly by the mass and proptosis was evident in 19. Medial (five cases) and lateral deviation (two cases) was less common and never marked. Slight flattening of the superior aspect of the globe was seen in 16 patients. In 15 patients the mass could be seen extending posterior to the globe. In most patients the lacrimal gland could not be distinguished on CT from the granuloma. There was often no plane of definition from the superior or lateral rectus muscles but the lesion always remained extraconal. The attenuation of the lesions was homogenous and approximately isodense with brain in all but two patients, in whom it was hypodense with no change after contrast enhancement. Measurements made in three patients showed the attenuation of the granuloma to range from 36 to 40 Hounsfield Units. There were no hyperdense lesions.
Magnetic Resonance The lesion showed strikingly higher signal than that of the intraorbital fat on both Tl-weighted inversion recovery and T2-weighted spin echo sequences (Fig. 6). The patient was also examined by CT and although the lesion
239
ORBITOFRONTAL CHOLESTEROL GRANULOMAS
(a)
(b)
(c) Fig. 3 - Three different cases showing typical CT features of cholesterol granuloma. (a) Direct coronal CT scan of the orbits showing an isointense (relative to brain) soft tissue mass markedly expanding the dip16e. The bony margins are very ragged and irregular in contrast to the plain film appearances of the same lesion (Fig. 1). The floor of the anterior cranial fossa is partially eroded (arrow). (b) Direct coronal CT showing marked inferior deviation of the globe by an intradipl6ic soft tissue mass which has extended into the orbit. There is extension into the zygomatic process (arrow). (c) Direct axial CT showing an isointense mass in the superotemporal quadrant of the orbit. The lateral bony margin of the lesion is irregular. The globe is displaced inferiorly.
was more readily apparent on MRI no useful additional information was gained from the M R study. In cases where full documentation was available for review, the correct diagnosis was made or thought to be the likeliest differential preoperatively in 60% of cases on the basis of clinical and radiological findings. The main alternative diagnosis was a dermoid cyst. DISCUSSION Orbitofrontal cholesterol granuloma is an uncommon lesion of unknown aetiology. On average over the last 17 years, 1.8 cases per year have been seen at this institution. This compares with approximately 2.5 cases per year of lacrimal gland carcinoma and 3.75 cases of pleomorphic adenoma of the lacrimal gland. Various terms have been used to describe cholesterol granuloma, including lipid granuloma, cholesteatoma, xanthomatosis, histiocytic granuloma, haematoma and chronic haematic cyst. These terms are either misleading or inaccurate and cholesterol granuloma is preferred. Histological appearances are highly specific, with cho-
lesterol clefts surrounded by foreign-body giant cells (Fig. 7). A crucial distinguishing feature from a dermoid is the absence of epithelial elements [3], which may explain why cholesterol granulomas so rarely recur after surgery. Earlier theories of the pathogenesis of cholesterol granuloma included a localized xanthomatosis and a histiocytosis X variant [4-6]. Cholesterol granulomas of the petrous bone have been studied more extensively and are thought to be related to impaired ventilation of aerated cavities resulting in mucosal oedema and haemorrhage [7,8]. Degradation of erythrocyte membranes results in deposition of cholesterol which subsequently crystallizes; the crystals then stimulate a granulomatous reaction. Clearly the initiating factors must be different in the lesions originating in nonpneumatized frontal bone. However, evidence of haemorrhage was present at surgery in all the cases described by McNab and Wright [2] whose composition overlaps with the present series, although the exact cause of haemorrhage is unclear. The frequency of a definite history of trauma is very variable, ranging from none of eleven cases [9], to up to one third of cases [2,3,10]. It is possible that the trauma may be mild and perhaps forgotten; the strong male preponderance in
240
CLINICAL RADIOLOGY
(a)
(b) Fig. 4 (a) Direct axial and (b) reformatted coronal CT showing fragments of bone around the periphery of the lesion. There is extensive destruction of the orbital roof with extension extradurally into the anterior cranial fossa.
Fig. 5 Direct coronal CT showing irregular erosion of the lateral orbital wall with extension into the temporal fossa. The lesion has also involved the lateral wall of the frontal sinus although the sinus remains fully aerated.
these and other reports and the high incidence of heavy manual occupations may reflect a traumatic aetiology. It has also been suggested that a dipl6ic anomaly may predispose to haemorrhage [3]. Cholesterol granulomas most commonly present with proptosis. Pain is not a marked feature but some patients complain o f a dull ache. Diplopia and blurred vision also occur. Surgical treatment involves aspiration of contents and stripping or curettage of the lining which is highly successful. One case in the current series recurred 2 years
after surgery and only one other possible recurrence has been reported in the literature [2,11]. Our series demonstrates that cholesterol granulomas have characteristic appearances on both plain radiographs and CT. The typical plain film appearance is of a well defined superotemporal osteolytic lesion with minimal or no surrounding sclerosis and a smooth or only slightly irregular border. Extension into the zygomatic process, as described by Lloyd [1] is frequent. At CT an isodense or hypodense, expanding lytic lesion produces ragged bone destruction and invariably extends extraperiosteally into the orbit, causing proptosis and inferior deviation of the globe in almost all cases. Extension into the anterior cranial and temporal fossae occurs less frequently. Bone spiculation or fragmentation may be seen in 50% of cases. The absence of this latter feature on plain films presumably reflects the superior contrast resolution of CT. Very similar appearances were described in a recent CT study of 11 patients in Holland [9] and in other reports [3,12,13]. Although in our series contrast enhancement was not observed in the five patients studied before and after contrast medium, enhancement has been reported in a single case [3]. Radiological differential diagnosis of a lytic lesion in the frontotemporal orbital margin includes lacrimal gland neoplasm, metastasis, dermoid or epidermoid cyst, aneurysmal bone cyst [14], eosinophilic granuloma [15], cystic ossifying fibroma, intradipl6ic meningioma [16], frontal sinus mucocoele and hydatid cyst. Carcinomas of the lacrimal gland, which together with dermoids repre-
241
ORBITOFRONTAL CHOLESTEROL GRANULOMAS
(~)
(a)
(b) Fig. 6 (a) Tl-weighted inversion recovery (TR 2100 ms, TI 500 ms) coronal MRI scan showing a markedly hyperintense mass in the superotemporal orbit which has eroded through the vault into the anterior cranial fossa and is displacing the frontal lobe. (b) T2-weighted •spin echo (TR 2000 ms, TE 80 ms) axial MRI showing signal hyperintensity.
sent the main differential diagnostic consideration on clinicoradiological grounds, but whose treatment is radically different, also cause irregular bone destruction with or without sclerosis. They may be denser than brain on CT, approximately one third containing calcification [17] and enhance with intravenous contrast medium. Dermoid cysts usually have a sclerotic border and do not extend into the zygomatic process [1]. On CT they may show a characteristic bony defect in the lateral orbital wall and two-thirds contain areas of low attenuation. Benign lacrimal gland tumours cause local pressure erosion with expansion of the lacrimal fossa. Cystic ossifying fibroma and eosinophilic granuloma characteristically have sclerotic margins. We encountered a frontal mucocoele which had several features suggestive of cholesterol granuloma except that it was hyperdense relative to brain, a feature not seen in any of the cholesterol granulomas in this or other reported series (Fig. 8). The single lesion studied by MRI showed a higher signal than intraorbital fat not only on T2 weighting but also on a heavily Tl-weighted inversion recovery sequence, reflecting the paramagnetic effects of haemoglobin degradation products. Similar appearances are reported by Fukuta and Jackson [13] in an orbital lesion and in studies of petrous bone lesions [18,19]. In one case [18] appearances were unchanged after intravenous gadolinium-DTPA. Few other lesions in the orbitofrontal region show similar M R characteristics; dermoid cysts may appear similar but more commonly give low signal on T1 weighting. However CT and plain
(b) Fig. 7 Photomicrographs of the wall of a cholesterol granuloma showing the characteristic arrangement of cholesterol clefts surrounded by a chronic inflammatory infiltrate including occasional giant cells. (Original magnification (a) x 100, (b) x 250.)
Fig. 8 Enhanced axial CT scan of a mucocoele extending into the orbit. It is hyperdense with respect to normal brain.
film appearances in combination could be expected to distinguish these entities. Cholesterol granulomas may be diagnosed with reasonable confidence on the basis of clinical and radiological data. Plain skull radiography shows a characteristic appearance with a very limited differential diagnosis. CT
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also has typical appearances and enables the surgeon to assess intraosseous and extraosseous spread preoperatively. Since surgery for lacrimal gland carcinoma is much more radical, awareness of the possibility of this benign lesion is very important, particularly as the initial impression of the CT appearance may be of an aggressive bonedestroying tumour. CT may also be helpful in assessing the other main differential diagnosis, a dermoid cyst. A role for three-dimensional CT for pre-surgical planning has been proposed [13] but this facility is not freely available. Limited experience with MRI shows that the lesion is well demonstrated but a role for M R I in management of these lesions is yet to be established; when the diagnosis is in doubt, however, the characteristic signal changes can be helpful. MRI would also be expected to delineate intracranial extension better than CT as well as defining intraorbital anatomy more clearly. The angiographic and radionuclide bone scan appearances of cholesterol granuloma have been reported [20,21] but are no longer likely to be of clinical relevance. Acknowledgements. We are grateful to Professor Alec Garner for providing Fig. 7 and to Mr John Wright whose patients comprise this series.
6 Nichols JVV. Cholesterol containing granuloma of the orbital wall. American-Journal of Ophthalmology 1956;41:234 247. 7 Beaumont GD. The effects of exclusion of air from pneumatised bones. Journal of Laryngology and Otology 1966;80:236 249. 8 Nager GT, Vanderveen TS. Cholesterol granuloma involving the temporal bone. Annals of Otology 1976;85:204-209. 9 Eijpe AA, Koornneef L, Verbeeten B Jr, Peeters FLM, Zonnefeld FW. Cholesterol granuloma of the frontal bone: CT diagnosis. Journal of Computer Assisted Tomography 1990; 14:914-917. 10 Ramsey GS, Laws HW, Pritchard JE, Elliot H. Post-traumatic granuloma of the bony orbit simulating tumour. Journal of the Canadian Medical Association 1948;59:206-211. 11 Pfeiffer RL, Nicholl RJ. Dermoids and epidermoids of the orbit.
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REFERENCES 1 Lloyd GAS. Cholesterol granutoma of the facial skeleton. British Journal of Radiology 1986;59:481-485. 2 McNab AA, Wright JE. Orbitofrontal cholesterol granuloma. Ophthalmology 1990;97:28 32. 3 Parke DW, Font RL, Boniuk M, McCrary JA. 'Cholesteatoma' of the orbit. Archives of Ophthalmology 1982;100:612 616. 4 Knapp A. Xanthomatosis of the orbit: report of two cases. Archives of Ophthalmology 1934;11:141-147. 5 Hanbery JW, Rayport M. Unilateral exophthalmos due to orbitofrontal cholesterol granuloma. American Journal of Surgery 1955;89:1144 1162.
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