Eur Radiol (2002) 12:2726–2729 DOI 10.1007/s00330-002-1359-5

C. Neugroschl P. David N. Sadeghi A. Soebert B. Pirotte S. Rorive D. Balériaux

Received: 7 August 2001 Revised: 27 December 2001 Accepted: 4 January 2002 Published online: 8 May 2002 © Springer-Verlag 2002 C. Neugroschl (✉) · P. David · N. Sadeghi D. Balériaux Department of Neuroradiology, Hôpital Erasme, Université Libre de Bruxelles, 808 Route de Lennik, 1070 Brussels, Belgium e-mail: [email protected] Tel.: +32-2-5554325 Fax: +32-2-5553994 A. Soebert Department of Neurology, Hôpital Bracops, Rue Docteur Huet 79, 1070 Brussels, Belgium

NEURO

Unusual CT features of dermoid cyst in the posterior fossa

B. Pirotte Department of Neurosurgery, Hôpital Erasme, Université Libre de Bruxelles, 808 Route de Lennik, 1070 Brussels, Belgium S. Rorive Department of Histology, Hôpital Erasme, Université Libre de Bruxelles, 808 Route de Lennik, 1070 Brussels, Belgium

Abstract A dermoid cyst of the posterior fossa in a 73-year-old man is reported. The presentation of the cyst was unusual because of the age of the patient, the spontaneously hyperdense aspect of the mass on CT,

Introduction Intracranial dermoid tumors are rare congenital lesions of the brain that account for 0.04–0.6% of all intracranial tumors [1, 2]. Intracranial dermoid cysts usually become symptomatic during the third decade with a slight male predilection [3]. We report a case of dermoid tumor in the posterior fossa discovered in a 73-year-old man with an unusual dense appearance on CT, high signal intensity on T1weighted MR images and low heterogeneous signal intensity on T2-weighted images. On gadolinium-enhanced T1weighted images, a partial rim enhancement was present.

Case report A 73-year-old man presented with a 1-month history of vertigo and instability. Since the first episode of dizziness, the patient complained of gait disturbance. More recently, the symptoms had

the partial rim enhancement of the lesion, and the presence of perilesional edema. On pathologic examination, the cyst contained small amount of fat, hairs, necrosis, and small areas of hemorrhage. The amount of hemorrhage found could not explain the spontaneous hyperdensity of the lesion found on CT. The hyperdensity may be related to high protein content of the lesion. Keywords Dermoid cyst · Brain · Intracranial · MRI

worsened. The clinical and neurological examinations were suggestive of vermian ataxia with gait deviation towards the right side. Non-enhanced brain CT scan showed a heterogeneous spontaneously hyperdense mass in the posterior fossa which had been considered as a lesion with associated hemorrhage. Some calcifications were present around the lesion and no low-intensity areas suggesting fat could be detected on CT (Fig. 1). On the basis of these CT findings, our differential diagnoses were cavernous angioma or giant aneurysm. On pre-contrast T1-weighted MR images, the lesion was lobulated with well-delineated borders and showed mixed signal intensity, markedly high signal intensity in the major part of the lesion, moderate to iso-signal intensity in some parts and scattered foci of low signal intensity (Fig. 2a). After administration of gadolinium, there was a partial rim enhancement (Fig. 2b). On T2-weighted images, the lesion was heterogeneous with large areas of low signal. High signal intensity area corresponding to mild edema surrounded the mass (Fig. 3). Magnetic resonance angiography and conventional angiography were performed and excluded the diagnosis of giant aneurysm or a highly vascularized tumor. The retained diagnosis before surgery was therefore an expansive lesion with hemorrhage including cavernoma vs hemorrhagic neoplasm.

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Fig. 1a, b A 73-year-old man with history of gait instability. Axial CT images without contrast injection show a heterogeneous mass in the posterior fossa with partially high-attenuating foci. Some peripheral calcifications are present (a). No low intensity areas suggesting fat can be detected

At surgery, total resection of the lesion was performed. The tumor was well capsulated and contained yellowish debris, some hemorrhage and crisp material with hair, and necrotic tissue (Fig. 4). Histologic examination of the cyst revealed characteristic features of a dermoid cyst consisting of stratified squamous epithelium, hair follicles, keratin necrotic tissue, cholesterol deposits, hemosiderin macrophages, and focal calcifications. The patient had a good postoperative recovery with total disappearance of the symptoms.

Fig. 2 a Axial non-enhanced T1-weighted image at the level of the posterior fossa. A well-lobulated mass shows heterogeneity with markedly high signal intensity in the right part of the lesion suggesting hemosiderin deposits due to intratumoral hemorrhage. b Axial T1-weighted image after gadolinium injection shows a partial peripheral enhancement of the lesion

Discussion Dermoid cysts are rare congenital malformative tumors usually located in the suprasellar, parasellar regions, and posterior fossa where most present either as midline le-

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Fig. 3 Axial T2-weighted MR image. The lesion appears heterogeneous with large areas of low signal. A high-intensity rim is surrounding the lesion corresponding to mild edema

sions between the cerebellar hemispheres or within the fourth ventricle [1, 3]. Dermoid lesions are slow-growing tumors and may become quite large before producing symptoms; however, symptoms from intracranial dermoids usually arise in the third decade of life, consisting of neural dysfunction caused by raised intracranial pressure or by obstructive hydrocephalus [4, 5]. A classical com-

Fig. 4 Gross pathology of the cyst. The mass has been opened to display its cheesy contents and hair

plication is caused by rupture of the cyst and spillage of the fatty material into the cerebrospinal fluid [6, 7]. The age of our patient was atypical for the diagnosis of dermoid cyst. Dermoid cysts classically contain skin adnexal structures such as hair follicles as well as sebaceous and sweat glands. Liquid secretions and products of these dermal appendages result in an oily mixture that contains lipid metabolites [8]; therefore, their most typical aspect is the presence of a low-density mass on CT, allowing an easy radiologic diagnosis of dermoid cyst containing lipids. In our patient there was no fatty tissue attenuation on CT and the amount of hemorrhage found at pathologic examination could not explain the spontaneous hyperdensity on CT. Hyperdense dermoid cysts have been reported but are uncommon [9, 10]. The dense appearance could be explained by a combination of high protein concentration and high viscosity of the cyst [9] or by intra-tumoral hemorrhage [10]. On MR imaging, dermoid cysts typically appear hyperintense on T1-weighted sequences, with variable signal on T2-weighted sequences that ranges from hypointense to inhomogeneously hyperintense [11]. Enhancement following contrast administration is uncommon; however, MR findings of dermoid cyst are variable. Smith et al. [11] reported the MR findings in seven patients with pathologically proven ruptured dermoid cyst: the mass was hypointense on T1-weighted images and inhomogeneously hyperintense on T2-weighted images in all cases. The content of those lesions was mostly keratin and cerebrospinal fluid with fewer lipids or liquefied cholesterol. In our patient, T1-weighted MR images were more typical, but the amount of cholesterol found at histology was too low to explain a significant increase

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in signal intensity especially since the CT aspect was not concordant with lipid deposits. The hyperdensity on CT and the hypersignal on MR T1-weighted images could be explained by the high protein content of the necrotic tissue within the lesion. In other tumors, such as craniopharyngiomas, some authors reported high protein concentration responsible for an increase in signal intensity on T1-weighted images [12]. Other unusual findings in our patient were the partial rim enhancement and the perilesional edema suggesting a slow-growing tumor.

Conclusion The age of the patient, the hyperdense aspect of the lesion on CT, and the presence of a rim enhancement made the radiologic diagnosis of a dermoid cyst difficult in this case. The dense appearance of the lesion on CT in our patient was not related to hemorrhage but rather to a high-protein concentration of the lesion.

References 1. Lunardi P, Missori P (1991) Supratentorial dermoid cysts. J Neurosurg 75:262–266 2. Rubin G, Scienza R, Pasqualin A, Rosta L, Da Pian R (1989) Craniocerebral epidermoids and dermoids. Acta Neurochir 97:1–16 3. Wilms G, Casselman J, Demaerel P et al. (1991) CT and MRI of ruptured intracranial dermoids. Neuroradiology 33:149–151 4. Gao P-Y, Osborn AG, Smirniotopoulos JG, Harris CP (1992) Epidermoid tumor of the cerebellopontine angle. Am J Neuroradiol 13:863–872

5. Miller NR, Epstein MH (1975) Giant intracranial dermoid cyst. Case report and review of the literature on intracranial dermoids and epidermoids. Can J Neurol Sci 2:127–134 6. Oursin C, Wetzel SG, Lyrer P, Bachli H, Stock KW (1999) Ruptured intracranial dermoid cyst. J Neurosurg Sci 43:217–-221 7. Nagele T, Klose U, Grodd W, Opitz H, Schick F, Steinbrecher A, Voigt K (1996) Three-dimensional chemical shift-selective MRI of a ruptured intracranial dermoid cyst. Neuroradiology 38:572–574 8. Smith AS (1989) Myth of the mesoderm: ectodermal origin of dermoids. Am J Neuroradiol 10:449 9. Drolshagen LF, Standefer M (1991) Dense dermoid cyst of the posterior fossa. Am J Neuroradiol 12:317

10. Mamata H, Matsumae M, Yanagimachi N, Matsuyama S, Takamiya Y, Tsugane R (1998) Parasellar dermoid tumor with intra-tumoral hemorrhage. Eur Radiol 8:1594–1597 11. Smith AS, Benson JE, Blaser SI et al. (1991) Diagnosis of ruptured intracranial dermoid cyst: value of MR over CT. Am J Neuroradiol 12:175–180 12. Ahmadi J, Destian S, Apuzzo MLJ, Segall HD, Zee C (1992) Cystic fluid in craniopharyngiomas: MR imaging and quantitative analysis. Radiology 182:783–785