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Aneurysmal bone cysts in the cranial vault and base of skull
Surg Neurol 1985;23:193-8
193
Aneurysmal Bone Cysts in the Cranial Vault and Base of Skull L. C a l l i a u w , M . D . , H . R o e l s , M . D . , a n d J. C a e m a e r t ,
M.D.
Department of Neurosurgery and Neuropathology, University Hospital of Ghent, Belgium
Calliauw L, Roels H, Caemaert J. Aneurysmal bone cysts in the cranial vault and base of skull. Surg Neurol 1985;23:193-8.
Three cases of aneurysmal bone cyst of the skull are reported. The localization in the base of the skull (two cases) is extremely rare and simulates a space-occupying intracerebral lesion. The clinical and microscopic findings, and their significance for the differential diagnosis f r o m malignant brain tumors, are described. KEY WORDS: Aneurysmal bone cyst; Cranial vault; Base of skull; Benign skull neoplasm
From the group o f giant cell tumors o f bone, Jaff6 [4] separated out the group of aneurysmal bone cysts. Those lesions have a specific behavior, a typical roentgenologic picture, and well-defined microscopic features. They occur generally in the metaphysial area of the tubular bones o f the extremities; 9 0 % of patients are under the age o f 20 yr. In neurosurgical patients they can be found in the vertebral column, but are nevertheless rare. The differential diagnosis between aneurysmal bone cyst o f the vertebrae and giant cell tumor has to be made because giant cell tumors show a malignant evolution in 10% of cases, whereas aneurysmal bone cysts are benign lesions and recurrence is only seen after incomplete removal. The distinctive conditions o f both lesions have been extensively described by Verbiest [14-16]. Localization o f aneurysmal bone cysts in the bones of the skull has rarely been mentioned. In the literature, 44 cases o f localization in the calvarian bones have been described, most frequently in the r o o f o f the orbit (11 cases) and in the occipital bone (13 cases). The temporal, frontal, and parietal bones have also been affected [1,2,4,6,8-10,12,13]. In only three cases was the base of the skull involved [3,11,17]. A special case is case 11 in the series o f Verbiest (benign tumors involving the cervical spine) [ 16]. H e r e
Address reprint requests..to: L. Calliauw, M.D., Neurosurgical Department, Akademisch Ziekenhuis, De Pintelaan 185, 9000 Ghent, Belgium. © 1985 by Elsevier Science Publishing Co., Inc.
the tumor was situated in the right and medial portion of the atlas and extended into the right posterior cranial fossa with destruction of the right atlanto-occipital joint. After a successful operation the patient had to be reoperated upon after 6 yr. T h e r e was tumor growth in the left suboccipital region with destruction of the left atlanto-occipital joint and growth into the occipital bone (margin of the foramen magnum). Although in this case the tumor is not exclusively intracranial, the problem of operability and prognosis is very similar. Most authors agree that aneurysmal bone cysts in the skull are readily recognizable pathological entities and that radical surgical removal is easily possible. However, in cases with localization in the base of the skull, diagnosis and treatment present particular difficulties and for this reason a description is given of three cases seen in our clinic--one case with localization in the cranial vault and two cases with localization in the base o f the skull.
Localization in the Cranial Vault Case 1 A 2-month-old boy was admitted to the neurosurgical clinic in October 1981. H e was born normally and at that time there was no swelling on the head. Twentyfour hours after birth a swelling started in the right parietal region that increased rapidly in size. At the time of admission it measured 4 cm in diameter and protruded 2 cm from the head. Neurological examination was negative. X-ray films of the skull revealed a lesion with a "blow-out" appearance (Figure 1). It was delimited by a thin shell o f bone; osseous septa could not be distinguished. Computed tomography was not performed and at operation the lesion was exposed by a horseshoe-shaped skin flap. The outer shell of bone was removed and tissue, appearing like old blood, was aspirated. Granulation tissue was easily peeled from the medial wall of the cyst. The inner wall was then clean but some troublesome bleeding was encountered, indicating a pathologic vascularization in that region. After careful hemostasis, the scalp wound was closed. The postoperative course was uneventful. 0090-3019/85/$3.30
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well vascularized. The degree of vascularization increased toward the lumen of the cyst. The wall was covered by fibrin and red blood cells. The stroma also contained red blood cells and iron-loaded histiocytes (Figure 2). The pathologic diagnosis was that of an aneurysmal bone cyst.
Localization in the Base of the Skull
Case 2
Figure 1. Case I. Skull film, right lateral view, showing the "blow-out" appearance.
The patient was seen 2 yr after the operation. The head circumference was 48.5 cm and on palpation the cranial vault was normal.
Microscopicfindings. The wall o f the cyst was thick and was composed o f collagen-rich fibrous tissue, which was
A 36-year-old man had two epileptic seizures 6 months before he was admitted in October 1981. T h r e e weeks before admission he began to suffer from deafness in the left ear, followed soon by left facial palsy and sensory loss in the three branches of the left trigeminal nerve. There was no history of prior trauma to his head.
Examination. The patient had a left infranuclear facial palsy and a hypoesthesia in the entire distribution of the left trigeminal nerve. T h e r e was a marked hypoacusia in the left ear. The tendon reflexes were increased in both arms and legs; on the right side a positive Babinski's sign was found. T h e r e was also a slight dys-
Figure 2. Case 1. Photomicrograph of the wall of the cyst. The wall is covered by fibrin and red blood cells (H&E stain: × 64~.
Cranial Aneurysmal Bone Cysts
Surg Neurol 1985;23:193-8
195
metria in the right arm. Plain roentgenograms of the skull were entirely normal. Computed tomography (Figure 3) confirmed the presence of an expanding lesion in the left fossa temporalis; there was a displacement of the left lateral ventricle to the right and the lesion appeared as a multiloculated lesion. The periphery was hyperdense; after contrast medium injection this high density enhanced. In the center, areas of low density were separated by septa; after contrast medium injection they remained unchanged. The diagnosis of malignant brain tumor was made on the basis of this picture.
Operation. A large left-sided temporal craniotomy was made. Under the temporal lobe a large encapsulated mass was seen extradurally. After opening o f the capsule it appeared that the lesion was made o f cystic cavities filled with old blood. The contents of these cysts were aspirated. The surface o f the base of the skull was eroded and this extended to the ala magna o f the sphenoid bone; the sphenoid sinuses were not open. T h e foramen spinosum and foramen ovale were eroded. In the cavities of the tumor was granular tissue, which was removed. The bone flap, with a normal aspect, was replaced.
Figure 3. Case 2. Computed tomography scan (alter contrast medium injection). Note the picture of a multiloculated lesion within the center and areas of low density separated by septa.
Figure 4. Case 2. Photomicrograph of the wall of the cyst. Numerous multinuclear giant cells are seen ~H&E stain," x 64~.
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The postoperative course was uneventful. After 3 mo there were signs of reinnervation of the facial nerve. On the last examination, 2.5 years after the operation, the hypoesthesia in the distribution o f the left trigeminal nerve had disappeared, but the patient remained deaf in the left ear and there was still weakness o f the muscles innervated by the left facial nerve.
Microscopicfindings. T h e lesion was formed of a number of cavernous vascular spaces. T h e biopsy showed the thick wall o f the cyst, which contained red blood cells, numerous multinucleated giant cells, and fibroblasts. Because o f the great number o f osteoclasts, the lesion in some places simulated a giant cell tumor. In other places, however, the wall was lined by flat endothelial like cells, and a thin layer o f fusiform fibroblasts (Figure 4). The National Council for Bone Tumours, after reexamination, confirmed the diagnosis o f aneurysmal bone cyst. T h e r e was no evidence here of any preexisting vascular malformation. Case 3 A 19-year-old woman began in January 1982 to have pain in the left temporal region. By the time she was admitted to the department o f ophthalmology there was a slight exophthalmia on the left side and she began to complain of diplopia. Neurological examination revealed no other abnormalities. On the left side there was a limitation of extraocular movements. Results o f the examination of the fundus were normal. Roentgenograms of the skull and orbit showed no abnormalities. The computed tomography scan (Figure 5) showed a mass lesion in the anterior part o f the left fossa temporalis with destruction o f the upper part of the orbit. This lesion enhanced after contrast medium injection; this enhancement was diffuse and it was impossible to ascertain if the lesion was multiloculated. A subsequent arteriogram o f the left common carotid and external carotid arteries demonstrated a mass lesion in the anterior part o f the temporal fossa; there was no vascular blush or visible supply from the external carotid artery. At the operation the squama o f the left temporal bone was eroded and the anterior part of the temporal fossa was filled with a tense extradural mass. The capsule was opened and straw-colored fluid was aspirated. The lesion was situated in the ala magna of the sphenoid bone and had destroyed the upper part of the orbit. Grayish, granular tissue was removed from the wall of the cavity. The postoperative course was uneventful. The patient was last seen 1.5 yr after the operation. At that time she had no complaints. The exophthalmia had disappeared and the ocular movements were normal.
Calliauw et al
Histological examination. The wall of the cyst was composed of fibrous tissue that was in some places very rich in vessels, which were infiltrated by histiocytes that frequently contained hemosiderin. The presence of some multinuclear giant cells of the osteoclastic type was noted. The underlying bone showed signs of remodeling and reaction with osteoblastic activity, swollen osteocytes, and some osteoclastic activity (Figure 6). Discussion The aneurysmal bone cyst described in our first patient is the usual clinical presentation of this nonneoplastic dysplasia. It was an externally visible lump, tender to palpation, and sometimes painful. Untreated it may attain impressive size. As both the inner and outer tables of the skull may be involved, a variable degree o f intracranial mass effect can be associated. Cases with choked disks and symptoms of compression of the brain occasionally occur. Even a rupture into the brain parenchyma of the temporal lobe, giving rise to an intracerebral hemorrhage, has been described [5]. The term aneurysmal, proposed by Jaff~ [4], has no meaning other than to imply the x-ray appearance of a "blow-out." This blow-out can occur suddenly, as seen in our case. In no other description in the literature-except for the patient with the intracerebral hemorr h a g e - c o u l d we find such a clear-cut sudden onset. This onset is in favor of the vascular nature o f the preexisting lesion. The fact that such a vascular lesion is never seen on selective arteriograms or at operation can be attributed to the obliteration of the vessels of that lesion when the blow-out occurs. Serial radiographs could perhaps permit a better understanding of the etiology and usual course of these cysts. In analogy, according to Mirra [7], who studied the aneurysmal bone cysts in the metaphyses of long bones, these cysts go through three phases that could be described as the incipient, midphase, and stabilization phases. The small, lytic lesions o f the incipient phase have not been recognized in the bones o f the skull, nor they have been confused with other entities. Our case 1 is an example of a cyst in the midphase of d e v e l o p m e n t - - a rapidly destructive growth phase. Within several weeks the lesion reached a maximal size with the classic blow-out features. The bone was tremendously expanded and in the periostal region there was no bony circumscription at that time. At operation blood and serosanguinous fluid were found. It seems that trauma was not a precipitating agent. T h e r e is no difficulty in making a radical surgical removal when these cysts are situated in the calvarian bones. As already mentioned, recurrence is not seen after radical removal.
Cranial Aneurysmal Bone Cysts
Figure 5. Case 3. Computed tomography scan (after contrast medium injection). Note the mass lesion in the anterior part of the left fossa temporalis.
Surg Neurol 1985;23:193-8
197
In our cases 2 and 3 the cysts were in the base of the skull. They were probably in the stabilization phase and growing slowly. Throughout their development they simulated an expanding cerebral lesion and we expected to find a malignant brain tumor at operation. Considering retrospectively the examination done before the operation, we found nothing to avoid this misdiagnosis. Plain roentgenograms of the skull mostly fail here to disclose abnormalities and only after the operation did we notice some suggestive alterations. Serial cerebral angiography indicated only the expanding lesion. Sometimes there is a slight increase in density in the venous phase but no vascular blush in the lesion; mostly these lesions are avascular. Occasionally larger arteries leading to the cyst are found, indicating an increase in blood supply, but all this is not typical and in general the diagnosis of brain tumor is suggested. Aneurysmal bone cysts have rarely been studied by computed tomography (only three cases to the best of our knowledge). Sometimes the multiloculated aspect,
t
¸iii Figure 6. Case 3. Photomicrograph of the wall of the cyst. The fibrous tissue is very rich in vessels," some multinuclear giant cells are noted (H&E stain," x 64).
198
Surg N e u r o l 1985;23:193-8
with low-density cavities and enhancement o f other parts, can be suggestive but our experience is too little to ascertain n o w that the computed tomography scan is highly reliable for a preoperative diagnosis. Complete removal o f these cysts from the base o f the skull is impossible. The operation consists o f aspiration o f the contents and curettage o f the cavities. The number o f cases is too small and our postoperative observation too short to determine the o u t c o m e o f our patients. In analogy with skeletal aneurysmal bone cysts, treated only by simple curettage, we have to consider a recurrence rate o f 21%. In the five cases o f aneurysmal bone cysts involving the cervical spine, Verbiest saw o n e recurrence (the already mentioned case 11 with extension into the posterior cranial fossa). Therefore, the belief that aneurysmal bone cysts of the skull are easily removable is limited to those cysts localized in the cranial vault.
Dr. Michielsen, Dr. Van Vuchelen, and Dr. De Groef of the Department of Histopathology, St. Jans-Hospital in Brugge, Belgium, provided great help by making the histological diagnosis in case 1.
References 1. Cassotto A, Carcangiu ML, Orvieto P, et al. Kyste An6vrismal cr~nien. Neurochirurgie 1981;27:197-200. 2. Constantini FE, Iraci G, Benedetti A, et al. Aneurysmal bone cyst as an intracranial space-occupying lesion: case report. J Neurosurg 1966;255:205-7.
Calliauw et al
3. Delorit GJ, Summers GW. Aneurysmal bone cyst of the sphenoid sinus. Trans Am Acad Ophthalmol Otolaryngo11975;80:438-43. 4. Jaff6 HL. Tumors and tumorous conditions of the bones and joints. Philadelphia, Lea & Febiger, 1958:54-62. 5. Keuskamp PA, Horoupian DS, Fein JM. Aneurysmal bone cyst of the temporal bone presenting as a spontaneous intracerebral hemorrhage: case report. Neurosurgery 1980;7:166-170. 6. Luccarelli G, Fornari M, Savoiardo M. Angiography and computerized tomography in the diagnosis of aneurysmal bone cyst of the skull. J Neurosurg 1980;53:113-6. 7. Mirra JM. Bone tumors. Diagnosis and treatment. Philadelphia, Lippincott, 1980. 8. Mufti SM. Aneurysmal bone cyst of the skull. J Neurosurg 1978;49:730-3. 9. O'Gorman AM, Kirkham TH. Aneurysmal bone cyst of the orbit with unusual angiographic features. AJR 1976;126:896-9. 10. Rao KVC, Rao BS, Reddy CP, et al. Aneurysmal bone cyst of the skull. J Neurosurg 1977;47:633-6. 11. Revuelta M, Jos VL, Trujillo F, et al. Dos casos raros de tumor de la base del craneo: osteoclastoma y quiste oseo aneurismatico. Rev Esp Otoneurooftalmol Neurocir 1975;33:19-23. 12. Scharfetter F. Eine aneurysmatische Knochenzyste des Os occipitale mit den neurologischen Zeichen eines Kleinhirntumors. Schweiz Arch Neurol Psych 1966;98:40-7. 13. Turgay Bilge, Oguzhan Coban, Beghan Ozden, et al. Aneurysmal bone cysts of the occipital bone. Surg Neurol 1983;20:227-30. 14. Verbiest H. Giant-cell tumours and aneurysmal bone cysts of the spine. J Bone Joint Surg 1965;47:699-713. 15. Verbiest H. Lesions of the cervical spine: a critical review. In: Carrea R (ed). Neurological surgery, international congress series 433. Amsterdam, Excerpta Medica, 1978:374-83. 16. Verbiest H. Tumors involving the cervical spine. In: Cervical Spine Research Society (ed). The cervical spine. Philadelphia, Lippincott, 1983:430-77. 17. Yee RD, Cogan DC, Thorp TR, et al. Optic nerve compression due to aneurysmal bone cyst. Arch Ophthalmol 1977 ;95:2176-9.
193
Aneurysmal Bone Cysts in the Cranial Vault and Base of Skull L. C a l l i a u w , M . D . , H . R o e l s , M . D . , a n d J. C a e m a e r t ,
M.D.
Department of Neurosurgery and Neuropathology, University Hospital of Ghent, Belgium
Calliauw L, Roels H, Caemaert J. Aneurysmal bone cysts in the cranial vault and base of skull. Surg Neurol 1985;23:193-8.
Three cases of aneurysmal bone cyst of the skull are reported. The localization in the base of the skull (two cases) is extremely rare and simulates a space-occupying intracerebral lesion. The clinical and microscopic findings, and their significance for the differential diagnosis f r o m malignant brain tumors, are described. KEY WORDS: Aneurysmal bone cyst; Cranial vault; Base of skull; Benign skull neoplasm
From the group o f giant cell tumors o f bone, Jaff6 [4] separated out the group of aneurysmal bone cysts. Those lesions have a specific behavior, a typical roentgenologic picture, and well-defined microscopic features. They occur generally in the metaphysial area of the tubular bones o f the extremities; 9 0 % of patients are under the age o f 20 yr. In neurosurgical patients they can be found in the vertebral column, but are nevertheless rare. The differential diagnosis between aneurysmal bone cyst o f the vertebrae and giant cell tumor has to be made because giant cell tumors show a malignant evolution in 10% of cases, whereas aneurysmal bone cysts are benign lesions and recurrence is only seen after incomplete removal. The distinctive conditions o f both lesions have been extensively described by Verbiest [14-16]. Localization o f aneurysmal bone cysts in the bones of the skull has rarely been mentioned. In the literature, 44 cases o f localization in the calvarian bones have been described, most frequently in the r o o f o f the orbit (11 cases) and in the occipital bone (13 cases). The temporal, frontal, and parietal bones have also been affected [1,2,4,6,8-10,12,13]. In only three cases was the base of the skull involved [3,11,17]. A special case is case 11 in the series o f Verbiest (benign tumors involving the cervical spine) [ 16]. H e r e
Address reprint requests..to: L. Calliauw, M.D., Neurosurgical Department, Akademisch Ziekenhuis, De Pintelaan 185, 9000 Ghent, Belgium. © 1985 by Elsevier Science Publishing Co., Inc.
the tumor was situated in the right and medial portion of the atlas and extended into the right posterior cranial fossa with destruction of the right atlanto-occipital joint. After a successful operation the patient had to be reoperated upon after 6 yr. T h e r e was tumor growth in the left suboccipital region with destruction of the left atlanto-occipital joint and growth into the occipital bone (margin of the foramen magnum). Although in this case the tumor is not exclusively intracranial, the problem of operability and prognosis is very similar. Most authors agree that aneurysmal bone cysts in the skull are readily recognizable pathological entities and that radical surgical removal is easily possible. However, in cases with localization in the base of the skull, diagnosis and treatment present particular difficulties and for this reason a description is given of three cases seen in our clinic--one case with localization in the cranial vault and two cases with localization in the base o f the skull.
Localization in the Cranial Vault Case 1 A 2-month-old boy was admitted to the neurosurgical clinic in October 1981. H e was born normally and at that time there was no swelling on the head. Twentyfour hours after birth a swelling started in the right parietal region that increased rapidly in size. At the time of admission it measured 4 cm in diameter and protruded 2 cm from the head. Neurological examination was negative. X-ray films of the skull revealed a lesion with a "blow-out" appearance (Figure 1). It was delimited by a thin shell o f bone; osseous septa could not be distinguished. Computed tomography was not performed and at operation the lesion was exposed by a horseshoe-shaped skin flap. The outer shell of bone was removed and tissue, appearing like old blood, was aspirated. Granulation tissue was easily peeled from the medial wall of the cyst. The inner wall was then clean but some troublesome bleeding was encountered, indicating a pathologic vascularization in that region. After careful hemostasis, the scalp wound was closed. The postoperative course was uneventful. 0090-3019/85/$3.30
194
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Calliauw et al
well vascularized. The degree of vascularization increased toward the lumen of the cyst. The wall was covered by fibrin and red blood cells. The stroma also contained red blood cells and iron-loaded histiocytes (Figure 2). The pathologic diagnosis was that of an aneurysmal bone cyst.
Localization in the Base of the Skull
Case 2
Figure 1. Case I. Skull film, right lateral view, showing the "blow-out" appearance.
The patient was seen 2 yr after the operation. The head circumference was 48.5 cm and on palpation the cranial vault was normal.
Microscopicfindings. The wall o f the cyst was thick and was composed o f collagen-rich fibrous tissue, which was
A 36-year-old man had two epileptic seizures 6 months before he was admitted in October 1981. T h r e e weeks before admission he began to suffer from deafness in the left ear, followed soon by left facial palsy and sensory loss in the three branches of the left trigeminal nerve. There was no history of prior trauma to his head.
Examination. The patient had a left infranuclear facial palsy and a hypoesthesia in the entire distribution of the left trigeminal nerve. T h e r e was a marked hypoacusia in the left ear. The tendon reflexes were increased in both arms and legs; on the right side a positive Babinski's sign was found. T h e r e was also a slight dys-
Figure 2. Case 1. Photomicrograph of the wall of the cyst. The wall is covered by fibrin and red blood cells (H&E stain: × 64~.
Cranial Aneurysmal Bone Cysts
Surg Neurol 1985;23:193-8
195
metria in the right arm. Plain roentgenograms of the skull were entirely normal. Computed tomography (Figure 3) confirmed the presence of an expanding lesion in the left fossa temporalis; there was a displacement of the left lateral ventricle to the right and the lesion appeared as a multiloculated lesion. The periphery was hyperdense; after contrast medium injection this high density enhanced. In the center, areas of low density were separated by septa; after contrast medium injection they remained unchanged. The diagnosis of malignant brain tumor was made on the basis of this picture.
Operation. A large left-sided temporal craniotomy was made. Under the temporal lobe a large encapsulated mass was seen extradurally. After opening o f the capsule it appeared that the lesion was made o f cystic cavities filled with old blood. The contents of these cysts were aspirated. The surface o f the base of the skull was eroded and this extended to the ala magna o f the sphenoid bone; the sphenoid sinuses were not open. T h e foramen spinosum and foramen ovale were eroded. In the cavities of the tumor was granular tissue, which was removed. The bone flap, with a normal aspect, was replaced.
Figure 3. Case 2. Computed tomography scan (alter contrast medium injection). Note the picture of a multiloculated lesion within the center and areas of low density separated by septa.
Figure 4. Case 2. Photomicrograph of the wall of the cyst. Numerous multinuclear giant cells are seen ~H&E stain," x 64~.
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The postoperative course was uneventful. After 3 mo there were signs of reinnervation of the facial nerve. On the last examination, 2.5 years after the operation, the hypoesthesia in the distribution o f the left trigeminal nerve had disappeared, but the patient remained deaf in the left ear and there was still weakness o f the muscles innervated by the left facial nerve.
Microscopicfindings. T h e lesion was formed of a number of cavernous vascular spaces. T h e biopsy showed the thick wall o f the cyst, which contained red blood cells, numerous multinucleated giant cells, and fibroblasts. Because o f the great number o f osteoclasts, the lesion in some places simulated a giant cell tumor. In other places, however, the wall was lined by flat endothelial like cells, and a thin layer o f fusiform fibroblasts (Figure 4). The National Council for Bone Tumours, after reexamination, confirmed the diagnosis o f aneurysmal bone cyst. T h e r e was no evidence here of any preexisting vascular malformation. Case 3 A 19-year-old woman began in January 1982 to have pain in the left temporal region. By the time she was admitted to the department o f ophthalmology there was a slight exophthalmia on the left side and she began to complain of diplopia. Neurological examination revealed no other abnormalities. On the left side there was a limitation of extraocular movements. Results o f the examination of the fundus were normal. Roentgenograms of the skull and orbit showed no abnormalities. The computed tomography scan (Figure 5) showed a mass lesion in the anterior part o f the left fossa temporalis with destruction o f the upper part of the orbit. This lesion enhanced after contrast medium injection; this enhancement was diffuse and it was impossible to ascertain if the lesion was multiloculated. A subsequent arteriogram o f the left common carotid and external carotid arteries demonstrated a mass lesion in the anterior part o f the temporal fossa; there was no vascular blush or visible supply from the external carotid artery. At the operation the squama o f the left temporal bone was eroded and the anterior part of the temporal fossa was filled with a tense extradural mass. The capsule was opened and straw-colored fluid was aspirated. The lesion was situated in the ala magna of the sphenoid bone and had destroyed the upper part of the orbit. Grayish, granular tissue was removed from the wall of the cavity. The postoperative course was uneventful. The patient was last seen 1.5 yr after the operation. At that time she had no complaints. The exophthalmia had disappeared and the ocular movements were normal.
Calliauw et al
Histological examination. The wall of the cyst was composed of fibrous tissue that was in some places very rich in vessels, which were infiltrated by histiocytes that frequently contained hemosiderin. The presence of some multinuclear giant cells of the osteoclastic type was noted. The underlying bone showed signs of remodeling and reaction with osteoblastic activity, swollen osteocytes, and some osteoclastic activity (Figure 6). Discussion The aneurysmal bone cyst described in our first patient is the usual clinical presentation of this nonneoplastic dysplasia. It was an externally visible lump, tender to palpation, and sometimes painful. Untreated it may attain impressive size. As both the inner and outer tables of the skull may be involved, a variable degree o f intracranial mass effect can be associated. Cases with choked disks and symptoms of compression of the brain occasionally occur. Even a rupture into the brain parenchyma of the temporal lobe, giving rise to an intracerebral hemorrhage, has been described [5]. The term aneurysmal, proposed by Jaff~ [4], has no meaning other than to imply the x-ray appearance of a "blow-out." This blow-out can occur suddenly, as seen in our case. In no other description in the literature-except for the patient with the intracerebral hemorr h a g e - c o u l d we find such a clear-cut sudden onset. This onset is in favor of the vascular nature o f the preexisting lesion. The fact that such a vascular lesion is never seen on selective arteriograms or at operation can be attributed to the obliteration of the vessels of that lesion when the blow-out occurs. Serial radiographs could perhaps permit a better understanding of the etiology and usual course of these cysts. In analogy, according to Mirra [7], who studied the aneurysmal bone cysts in the metaphyses of long bones, these cysts go through three phases that could be described as the incipient, midphase, and stabilization phases. The small, lytic lesions o f the incipient phase have not been recognized in the bones o f the skull, nor they have been confused with other entities. Our case 1 is an example of a cyst in the midphase of d e v e l o p m e n t - - a rapidly destructive growth phase. Within several weeks the lesion reached a maximal size with the classic blow-out features. The bone was tremendously expanded and in the periostal region there was no bony circumscription at that time. At operation blood and serosanguinous fluid were found. It seems that trauma was not a precipitating agent. T h e r e is no difficulty in making a radical surgical removal when these cysts are situated in the calvarian bones. As already mentioned, recurrence is not seen after radical removal.
Cranial Aneurysmal Bone Cysts
Figure 5. Case 3. Computed tomography scan (after contrast medium injection). Note the mass lesion in the anterior part of the left fossa temporalis.
Surg Neurol 1985;23:193-8
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In our cases 2 and 3 the cysts were in the base of the skull. They were probably in the stabilization phase and growing slowly. Throughout their development they simulated an expanding cerebral lesion and we expected to find a malignant brain tumor at operation. Considering retrospectively the examination done before the operation, we found nothing to avoid this misdiagnosis. Plain roentgenograms of the skull mostly fail here to disclose abnormalities and only after the operation did we notice some suggestive alterations. Serial cerebral angiography indicated only the expanding lesion. Sometimes there is a slight increase in density in the venous phase but no vascular blush in the lesion; mostly these lesions are avascular. Occasionally larger arteries leading to the cyst are found, indicating an increase in blood supply, but all this is not typical and in general the diagnosis of brain tumor is suggested. Aneurysmal bone cysts have rarely been studied by computed tomography (only three cases to the best of our knowledge). Sometimes the multiloculated aspect,
t
¸iii Figure 6. Case 3. Photomicrograph of the wall of the cyst. The fibrous tissue is very rich in vessels," some multinuclear giant cells are noted (H&E stain," x 64).
198
Surg N e u r o l 1985;23:193-8
with low-density cavities and enhancement o f other parts, can be suggestive but our experience is too little to ascertain n o w that the computed tomography scan is highly reliable for a preoperative diagnosis. Complete removal o f these cysts from the base o f the skull is impossible. The operation consists o f aspiration o f the contents and curettage o f the cavities. The number o f cases is too small and our postoperative observation too short to determine the o u t c o m e o f our patients. In analogy with skeletal aneurysmal bone cysts, treated only by simple curettage, we have to consider a recurrence rate o f 21%. In the five cases o f aneurysmal bone cysts involving the cervical spine, Verbiest saw o n e recurrence (the already mentioned case 11 with extension into the posterior cranial fossa). Therefore, the belief that aneurysmal bone cysts of the skull are easily removable is limited to those cysts localized in the cranial vault.
Dr. Michielsen, Dr. Van Vuchelen, and Dr. De Groef of the Department of Histopathology, St. Jans-Hospital in Brugge, Belgium, provided great help by making the histological diagnosis in case 1.
References 1. Cassotto A, Carcangiu ML, Orvieto P, et al. Kyste An6vrismal cr~nien. Neurochirurgie 1981;27:197-200. 2. Constantini FE, Iraci G, Benedetti A, et al. Aneurysmal bone cyst as an intracranial space-occupying lesion: case report. J Neurosurg 1966;255:205-7.
Calliauw et al
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