Intracranial dermoid cysts are congenital, rare and slow growing tumors derived from ectopic epithelial cells with an incidence of 0.04-0.7 of intracranial tumors. Although their nature is benign, they can cause significant morbidity through compression of neurovascular structures and rarely, rupture into subarachnoid space. Transient vasospasm due to mass effect or disseminated fat droplets lead to cerebral ischemia and subsequent motor and/or sensory hemisyndrome. We report an 18_year_old man presented with right side hemiparesis and paresthesia that radiologic investigations revealed a large suprasellar dermoid cyst and fat droplets in left sylvian fissure and subarachnoid space. Surgical resection done for him and pathological examinations confirmed the diagnosis.
Key words: Intracranial, dermoid, rupture, transient vasospasm
Introduction
Intracranial dermoid cysts are rare, congenital and usually benign lesions that consisting 0.04-0.7% of intracranial tumors (1). They may cause focal neurologic deficit through compression of adjacent neurovascular structures or rarely rupture, although they are usually asymptomatic and detected accidentally (2). Ruptured dermoid cysts and presence of fat droplets in subarachnoid space and ventricular system may cause chemical meningitis, hydrocephalous, vasospasm and cerebral ischemia (3). In this report, we present a ruptured intracranial dermoid cyst, manifesting as a cerebral ischemia with right side hemiparesis.
Case Report
An 18_year_old man presented with right upper extremity weakness and paresthesia since 1 week prior to admission. His symptoms progressed over 2 days and involved right lower extremity and mouth; then, paresthesia subsided and became restricted to his right hand but weakness continued. He had history of one unprovoked seizure in childhood; his past medical history was otherwise unremarkable. On presentation, muscle bulk was normal. The right arm muscle tone was normal; muscle strength was 4+/5 in right deltoid, biceps, and triceps and 2/5 in right wrist extensors and flexors. In addition, the right leg muscle tone was normal, but muscle strength was 3/5 in proximal and distal muscles. He had right side hyperreflexia and babinski sign; examination was otherwise unremarkable. Brain CT scan revealed a suprasellar lesion including a large low density area and small area of high density. In addition, CT scan demonstrated numerous low attenuation areas of fat density within inter hemispheric fissure, left sylvian fissure and left side subarachnoid space (Figure 1). Brain MRI showed a mass with high signal intensities on T1W, T2W but without evidence of acute infarction on DWI sequences. In addition, there were hyper-intense areas in the inter hemispheric fissure, left sylvian fissure and left side subarachnoid spaces (Figure 2). Patient’s clinical history and imaging findings steered us towards the diagnosis of ruptured dermoid cyst. He underwent right pterional craniotomy and excision of the mass. The patient’s postoperative course was uneventful with improvement of weakness. Pathological investigations confirmed the diagnosis of demoid cyst (Figure 3).
Discussion
Intracranial dermoid cysts are congenital lesions that emerge from the inclusion of ectodermal elements at the time of neural tube closure between 3rd and 5th weeks of embryogenesis(4). They are usually seen in the midline, most commonly infratentorial, either in the 4th ventricle cavity or in the vermis; outside the suprasellar region, supratentorial dermoid cysts are rare (5,6). Posterior fossa dermoids typically present in the first decade of life as a result of compression effect on the fourth ventricle followed by hydrocephalus, while supratentorial dermoids often presents in the second or third decades of life(7). Dermoid inclusion cysts have thick wall coated by stratified squamous epithelium and contain sweat and sebaceous glands, as well as hair follicles and teeth, although some individuals may have not all of the ectodermal components (8). They are benign, slow growing tumors usually detected accidentally; however, they may cause focal neurologic deficits as a result of encasement of adjacent neurovascular structures and rarely, rupture(2). The rupture is usually spontaneous, even though it may follow closed head injury or surgery (9,10). Stendel et al. (11), hypothesized that glandular secretions, increased by age dependent hormonal changes, may lead to fast enlargement and rupture; although, Lunardi and Missori (12) described that movements of head and brain pulsations promote rupture of cysts by their hammer-like effects. Rupture of dermoid cysts with ensuing dissemination of intracystic keratin and cholesterol breakdown products can cause a wide variety of symptoms (13). In addition, symptoms usually do not appear at the time of rupture but may be delayed from 3 months to 6.5 years after rupture, because the irritative effects of the spilled contents require time to evolve(7). The most common clinical presentation of ruptured dermoid cysts are headache (32.6%) followed by seizure (26.5%), cerebral ischemia with sensory and/or motor hemisyndrome (16.3%) and aseptic meningitis (8.2%) (14). Short term vasospasm can lead to local cerebral ischemia with a consequent transient neurologic deficits (15). The pathophysiology behind transient vasospasm and cerebral ischemia is not clearly understood; hypotheses have implicated rapidly growing cysts exerting mass effect on adjacent vessels and subsequent vasospasm and cerebral ischemia (11) as well as localized inflammatory arterial reaction followed by transient vasospasm (16). The case presented involved a spontaneously ruptured intracranial dermoid cyst causing transient vasospasm with subsequent cerebral ischemia. Imaging features of intracranial dermoid tumors on brain CT scans and MRI are virtually diagnostic (17). On CT scans, dermoid cysts can have mixed densities and occasionally, enhance following contrast administration. The intracystic fat components and disseminated fat droplets are seen as hypodense, whereas calcifications in the wall are hyperdense(17). On MRI scans, dermoid will be hyperintense on T1-weighted imaging, and heterogenous on T2-weighted imaging as a consequence of different components in the cyst such as bones, cartilage and calcifications (9,17). The fat content of dermoid cyst varies widely. If the internal fat content is relatively low, the lesion will seem as a cerebrospinal fluid (CSF)-like signal intensity. In such cases fat will appear hypersignal as compared to CSF on fluid attenuation inversion recovery (FLAIR) images, and therefore, can be differentiated from CSF containing arachnoid cyst (18). When a dermoid cyst ruptures, fat droplets floating within the nondependent portions of the ventricular system and/or subarachnoid space appear as hypodense on CT or hyperintense on T1W images (17). Although the imaging appearances of dermoid tumors are characteristic, several other intracranial lesions must be considered in the differential diagnosis, such as epidermoids, teratomas, lipomas, cystic craniopharyngioma and arachnoid cysts (7,9,17). Intradural dermoid cysts are four to nine times less common than epidermoids (7). Epidermoid and dermoid cysts both usually present as sharply defined, low density or intensity mass lesions with no contrast enhancement on CT and MRI (19); although, the location of epidermoid is more variable than dermoid cyst and shows greater deviation from midline (7). Differentiation between dermoid and epidermoid cysts may be prognostically important, because after complete or near total resection of dermoid cysts the recurrence is rare, contrary to epidermoids (20). Teratomas may contain fat that manifest as similar as dermoids but they usually enhance following contrast administration. Lipomas can be differentiated from dermoids based on their smooth borders and typical midline locations (9). Cystic craniopharyngiomas and arachnoid cysts can be distinguished from dermoids according to signal characteristics and presence of fat in dermoids seen on FLAIR sequences (7). Recurrence is rare in totally resected dermoids but is more common if there are retained portions of the tumor wall. Rare reports describe malignant transformation into squamous cell carcinoma in retained remnants of a dermoid tumor (4,17). Diffusion-weighted imaging helps to detect tumor remnants or re-growth after resection by showing hyperintensity due to high keratin content; thus, this protocol should be used for preoperative diagnostics and during follow-up period (21).
Conclusion
Intracranial dermoid tumor is a rare, congenital and usually benign neoplasm. Headache, seizure and motor and/or sensory hemisyndrome are the most common symptoms of dermoid. Transient vasospasm due to mass effect or localized inflammatory arterial reaction following rupture plays an important role in cerebral ischemia and subsequent motor and/or hemisyndrome. Radiographic features of fat containing lesion and calcification with mass effect are helpful for diagnosis of dermoid tumor. Physicians should be familiar with these characteristic findings, because the mortality and morbidity are reduced with early diagnosis and proper management.
