Neuro-radiology
Neuroradiology (1991) 33:349-351
9 Springer-Verlag 1991
Extradural epidermoid tumor of the frontal bone Ph. D e m a e r e l I , G. Wilms I , M. L a m m e n s 3, B. Nuttin 2, Ch. Plets 2, and A . L. Baert I Departments of 1 Radiology, 2 Neurosurgery, and 3 Neuropathology, University Hospitals K.U. Leuven, Leuven, Belgium Received: 15 December 1990
Summary. T h e r a d i o l o g i c findings in a case of a n e x t r a d u ral d i p l o i c e p i d e r m o i d t u m o r ( E T ) o f the f r o n t a l b o n e , e x a m i n e d with p l a i n X rays, C T a n d M R I , a r e r e p o r t e d . A h e a d injury with t r a u m a t i c inclusion o f e p i d e r m i s c o u l d h a v e b e e n t h e origin o f t h e tumor. This r e p o r t stresses t h e i m p o r t a n c e o f t h e p l a i n skull X r a y in t h e diagnosis of e x t r a d u r a l ET.
K e y words: E p i d e r m o i d cyst - M R i m a g i n g - B r a i n tumors
E p i d e r m o i d cysts are r a r e b e n i g n t u m o r s o f e c t o d e r m a l origin first d e s c r i b e d b y C r u v e i l h i e r in 1829 [2] a n d cons i d e r e d to o r i g i n a t e f r o m inclusions of e p i t h e l i a l cells d u r -
Fig.la, b. Skull X ray film. a Anteroposterior and b lateral projection show an osteolytic polylobular area with well-defined sclerotic (arrows) margins. The lesion is expansile and in close contact with the left orbit and frontal sinus
Fig. 2 a, b. CT scan. a Axial CE CT reveals a hypodense area with central isodense material. Erosions of outer and inner table are clear, as well as compression of the left frontal lobe. b Frontal CE CT shows the extent of the tumor
350
Fig. 3a-c. MRI. a SE axial T1 (600/15), b proton density (2500/22) and c T2WI (2500/90) demonstrate the typical signal intensities of an epidermoid tumor
Fig.& aBiopsy of the cyst wall showing the keratinized squamous epithelium (HE, 460 x ). b Cyst content composed of keratinous lamellae and cholesterol crystals (HE, 460 x )
ing the closure of the neural tube. Their incidence varies between 0.3 and 1.8% of intracranial tumors [1]. Posttraumatic epidermoid tumors have also been described [1, 3]. These tumors can be intra- or extradural. The extradural intradiploic epidermoid cysts have a typical appearance on the plain skull X ray. CT and MRI may be useful as additional examinations. We report a case of frontal extradural epidermoid cyst, examined by plain X rays of the skull, CT and MRI.
Case report A 41-year-old man presented with a severe headache. H e complained of a smooth, painless swelling of the left forehead. The mass increased in volume with sneezing and coughing.
His past medical history revealed a head injury 30 years ago at the same site as the present swelling. A plain skull X ray showed a polylobular osteolytic lesion of the left frontal bone with well defined sclerotic margins (Fig. 1). Erosion of both the inner and the outer table were seen. A contrast enhanced (CE) CT confirmed a large hypodense lesion in the left frontal bone without CE. A slightly hyperdense structure was observed in the cavity (Fig. 2). The lesion extended towards but was separate from the frontal sinus. On MRI the tumor appeared moderately hypointense on the SE T l W I (600/15), hyperintense on the proton density images (2500/22) and strongly hyperintense on the T2WI (2500/90) (Fig. 3). The differential diagnosis included (muco)pneumatocoele and epidermoid cyst.
351 Based on the clinical presentation the preferential diagnosis was (muco)pneumatocoele. At operation a white smooth mass was found firmly adherent to the dura mater, compressing the intracranial structures, but separated from the frontal sinus. The cyst, about 4 cm diameter and 2 cm thickness, was lined by simple stratified squamous keratinized epithelium (Fig. 4 a). Its flaky content was composed of multiple lamellae of keratinous material and cholesterol crystals (Fig. 4 b). The final diagnosis was epidermoid tumor.
Discussion Primary epidermoid tumors (ET) are rare benign, congenital neoplasm resulting from migration abnormalities of epithelial cells [1]. Macroscopically they appear as white smooth tumors. Microscopically they are outlined by a thin capsule of stratified keratinized squamous epithelium. Desquamation results in production of keratin and cholesterin [4, 5]. These primary E T can be differentiated in intra- and extradural lesions. The former show a predilection for the cerebellopontine angle and the parapontine region and constitute 75% of the primary E T [6]. The extradural lesions are usually found in the diploe and the scalp. The intradural lesions are characterized by a very slow evolution and may reach a considerable size at the time of diagnosis. The extradural lesions have a characteristic roentgenologic pattern and a typical clinical presentation of headache and a painless subcutaneous swelling. It is generally accepted that E T may also follow injury due to inclusion of epidermis. These secondary E T are histologically identical to the primary [1, 3, 7]. The head injury in our patient, 30 years ago, with traumatic inclusion of epidermis, could be the origin of the tumor, but there can be no certainty about this. Complications of E T are rare and include abscess formation, extradural hematoma and malignant degeneration [3]. Radiological studies are the cornerstone of their preoperative evaluation and especially in cases of intradural E T the CT and M R appearance are thought to be important in the diagnosis [9, 10]. In our case the plain X ray of the skull was pathognomonic. A typical roundish and polylobular bone erosion with well defined sclerotic margins was visualised. C E CT and MRI confirmed this diagnosis but in absence of the
plain skull X ray a correct diagnosis would have been less easy. In contrast to the MRI, it was possible to identify the mass separately from the frontal sinus on CT. On the other hand, the signal intensities on MRI were rather typical of ET. As described in the literature, the signal intensities on SE, T1 and T2 weighted images are due to the chemical state of cholesterin appearing as cholesterol crystals [6, 9, 20]. MRI is superior to CT in defining the anatomical limits and in differentiating E T from arachnoid cysts. On CT and MRI it was difficult to exclude a mucocoele.
Acknowledgements. The authors thank Mrs. L. Van Roey and Ms. D. Kiraly for technical assistance.
References 1. Rubin G, Scienza R, Pasqualin A, Rosta L, Da Pian R (1989) Craniocerebral epidermoids and dermoids. Acta Neurochir (Wien) 97:1-16 2. Cruveilhier J (1989) Cholest~atomes. Anatomie pathologique du corps humain. Paris, Bailliere 1,2:planche 6 3. Gros C, Vlahovitch B, Massaheb G, Roilgen A (1961) Kystes 6pidermoides intra-rachidiens par greffe 6pith61iale apr~s ponctions lombaires. Neurochirurgie 7:163-165 4. Vion-Dury J, Vincentelli F, Jiddane M, Van Bunnen Y, Rumeau C, Grisoli K Salomon G (1987) MR imaging of epidermoid cysts. Neuroradiology 29:333-338 5. Russel D, Rubinstein LJ (1989) Pathology of tumours of the nervous system, 5th edn. Edward Arnold, London Baltimore, pp 693-695 6. Olson JJ, Berk DW, Crawford SC, Menezes AH (1987) Comparative evaluation of intracranial epidermoid tumors with CT and MRI. Neurosurgery 21:357-361 7. Toglia JU, Netsky MG, Alexander E (1965) Epiderrnoid tumors of the cranium. J Neurosurg 23:384-393 8. Yanay Y, Tsuyi R, Ohmori S, Tatara N, Kabota S, Nagashima C (1985) Malignant change in an intradiploic epidermoid. Neurosurgery 16:252-256 9. Steffey D J, De Filipp GJ, Spera T, Gabrielsen TO (1988)MR imaging of primary epidermoid tumors. JCAT 12:438-440 10. Tampieri D, Melanson D, Ethier R (1989)MR imaging of epidermoid cysts. AJNR 10:351-356 Prof. Dr. G. Wilms Department of Radiology University Hospitals K.U. Leuven Herestraat 49 B-3000 Leuven Belgium
Neuroradiology (1991) 33:349-351
9 Springer-Verlag 1991
Extradural epidermoid tumor of the frontal bone Ph. D e m a e r e l I , G. Wilms I , M. L a m m e n s 3, B. Nuttin 2, Ch. Plets 2, and A . L. Baert I Departments of 1 Radiology, 2 Neurosurgery, and 3 Neuropathology, University Hospitals K.U. Leuven, Leuven, Belgium Received: 15 December 1990
Summary. T h e r a d i o l o g i c findings in a case of a n e x t r a d u ral d i p l o i c e p i d e r m o i d t u m o r ( E T ) o f the f r o n t a l b o n e , e x a m i n e d with p l a i n X rays, C T a n d M R I , a r e r e p o r t e d . A h e a d injury with t r a u m a t i c inclusion o f e p i d e r m i s c o u l d h a v e b e e n t h e origin o f t h e tumor. This r e p o r t stresses t h e i m p o r t a n c e o f t h e p l a i n skull X r a y in t h e diagnosis of e x t r a d u r a l ET.
K e y words: E p i d e r m o i d cyst - M R i m a g i n g - B r a i n tumors
E p i d e r m o i d cysts are r a r e b e n i g n t u m o r s o f e c t o d e r m a l origin first d e s c r i b e d b y C r u v e i l h i e r in 1829 [2] a n d cons i d e r e d to o r i g i n a t e f r o m inclusions of e p i t h e l i a l cells d u r -
Fig.la, b. Skull X ray film. a Anteroposterior and b lateral projection show an osteolytic polylobular area with well-defined sclerotic (arrows) margins. The lesion is expansile and in close contact with the left orbit and frontal sinus
Fig. 2 a, b. CT scan. a Axial CE CT reveals a hypodense area with central isodense material. Erosions of outer and inner table are clear, as well as compression of the left frontal lobe. b Frontal CE CT shows the extent of the tumor
350
Fig. 3a-c. MRI. a SE axial T1 (600/15), b proton density (2500/22) and c T2WI (2500/90) demonstrate the typical signal intensities of an epidermoid tumor
Fig.& aBiopsy of the cyst wall showing the keratinized squamous epithelium (HE, 460 x ). b Cyst content composed of keratinous lamellae and cholesterol crystals (HE, 460 x )
ing the closure of the neural tube. Their incidence varies between 0.3 and 1.8% of intracranial tumors [1]. Posttraumatic epidermoid tumors have also been described [1, 3]. These tumors can be intra- or extradural. The extradural intradiploic epidermoid cysts have a typical appearance on the plain skull X ray. CT and MRI may be useful as additional examinations. We report a case of frontal extradural epidermoid cyst, examined by plain X rays of the skull, CT and MRI.
Case report A 41-year-old man presented with a severe headache. H e complained of a smooth, painless swelling of the left forehead. The mass increased in volume with sneezing and coughing.
His past medical history revealed a head injury 30 years ago at the same site as the present swelling. A plain skull X ray showed a polylobular osteolytic lesion of the left frontal bone with well defined sclerotic margins (Fig. 1). Erosion of both the inner and the outer table were seen. A contrast enhanced (CE) CT confirmed a large hypodense lesion in the left frontal bone without CE. A slightly hyperdense structure was observed in the cavity (Fig. 2). The lesion extended towards but was separate from the frontal sinus. On MRI the tumor appeared moderately hypointense on the SE T l W I (600/15), hyperintense on the proton density images (2500/22) and strongly hyperintense on the T2WI (2500/90) (Fig. 3). The differential diagnosis included (muco)pneumatocoele and epidermoid cyst.
351 Based on the clinical presentation the preferential diagnosis was (muco)pneumatocoele. At operation a white smooth mass was found firmly adherent to the dura mater, compressing the intracranial structures, but separated from the frontal sinus. The cyst, about 4 cm diameter and 2 cm thickness, was lined by simple stratified squamous keratinized epithelium (Fig. 4 a). Its flaky content was composed of multiple lamellae of keratinous material and cholesterol crystals (Fig. 4 b). The final diagnosis was epidermoid tumor.
Discussion Primary epidermoid tumors (ET) are rare benign, congenital neoplasm resulting from migration abnormalities of epithelial cells [1]. Macroscopically they appear as white smooth tumors. Microscopically they are outlined by a thin capsule of stratified keratinized squamous epithelium. Desquamation results in production of keratin and cholesterin [4, 5]. These primary E T can be differentiated in intra- and extradural lesions. The former show a predilection for the cerebellopontine angle and the parapontine region and constitute 75% of the primary E T [6]. The extradural lesions are usually found in the diploe and the scalp. The intradural lesions are characterized by a very slow evolution and may reach a considerable size at the time of diagnosis. The extradural lesions have a characteristic roentgenologic pattern and a typical clinical presentation of headache and a painless subcutaneous swelling. It is generally accepted that E T may also follow injury due to inclusion of epidermis. These secondary E T are histologically identical to the primary [1, 3, 7]. The head injury in our patient, 30 years ago, with traumatic inclusion of epidermis, could be the origin of the tumor, but there can be no certainty about this. Complications of E T are rare and include abscess formation, extradural hematoma and malignant degeneration [3]. Radiological studies are the cornerstone of their preoperative evaluation and especially in cases of intradural E T the CT and M R appearance are thought to be important in the diagnosis [9, 10]. In our case the plain X ray of the skull was pathognomonic. A typical roundish and polylobular bone erosion with well defined sclerotic margins was visualised. C E CT and MRI confirmed this diagnosis but in absence of the
plain skull X ray a correct diagnosis would have been less easy. In contrast to the MRI, it was possible to identify the mass separately from the frontal sinus on CT. On the other hand, the signal intensities on MRI were rather typical of ET. As described in the literature, the signal intensities on SE, T1 and T2 weighted images are due to the chemical state of cholesterin appearing as cholesterol crystals [6, 9, 20]. MRI is superior to CT in defining the anatomical limits and in differentiating E T from arachnoid cysts. On CT and MRI it was difficult to exclude a mucocoele.
Acknowledgements. The authors thank Mrs. L. Van Roey and Ms. D. Kiraly for technical assistance.
References 1. Rubin G, Scienza R, Pasqualin A, Rosta L, Da Pian R (1989) Craniocerebral epidermoids and dermoids. Acta Neurochir (Wien) 97:1-16 2. Cruveilhier J (1989) Cholest~atomes. Anatomie pathologique du corps humain. Paris, Bailliere 1,2:planche 6 3. Gros C, Vlahovitch B, Massaheb G, Roilgen A (1961) Kystes 6pidermoides intra-rachidiens par greffe 6pith61iale apr~s ponctions lombaires. Neurochirurgie 7:163-165 4. Vion-Dury J, Vincentelli F, Jiddane M, Van Bunnen Y, Rumeau C, Grisoli K Salomon G (1987) MR imaging of epidermoid cysts. Neuroradiology 29:333-338 5. Russel D, Rubinstein LJ (1989) Pathology of tumours of the nervous system, 5th edn. Edward Arnold, London Baltimore, pp 693-695 6. Olson JJ, Berk DW, Crawford SC, Menezes AH (1987) Comparative evaluation of intracranial epidermoid tumors with CT and MRI. Neurosurgery 21:357-361 7. Toglia JU, Netsky MG, Alexander E (1965) Epiderrnoid tumors of the cranium. J Neurosurg 23:384-393 8. Yanay Y, Tsuyi R, Ohmori S, Tatara N, Kabota S, Nagashima C (1985) Malignant change in an intradiploic epidermoid. Neurosurgery 16:252-256 9. Steffey D J, De Filipp GJ, Spera T, Gabrielsen TO (1988)MR imaging of primary epidermoid tumors. JCAT 12:438-440 10. Tampieri D, Melanson D, Ethier R (1989)MR imaging of epidermoid cysts. AJNR 10:351-356 Prof. Dr. G. Wilms Department of Radiology University Hospitals K.U. Leuven Herestraat 49 B-3000 Leuven Belgium
