|Year : 2016 | Volume
| Issue : 1 | Page : 136-139
Fourth ventricle epidermoid tumor: Radiologic findings
Abhijit Patil, Vilas Kulkarni, Guneet Singh, Preeti Sehrawat
Department of Radiodiagnosis, Padmashree Dr. D. Y. Patil Medical College, Hospital and Research Centre, Dr. D. Y. Patil Vidyapeeth, Pimpri, Pune, Maharashtra, India
|Date of Web Publication||22-Dec-2015|
3-B, Khalsa College Colony, Patiala - 147001, Punjab
Source of Support: None, Conflict of Interest: None
Fourth ventricle epidermoid cysts or pearly tumors are uncommon lesions which arise from epithelial remnants at the time of neural tube closure. They are benign extracerebral intra-dural lesions accounting for <2% of intracranial tumors out of which only 5-18% may occur in the fourth ventricle. Epidermoid cysts of the fourth ventricle occur very rarely, with few cases reported in the literature. We present a case of a pathological proven less common fourth ventricle epidermoid cyst.
Keywords: Epidermoid cyst, fourth ventricle, hydrocephalus, magnetic resonance imaging
|How to cite this article:|
Patil A, Kulkarni V, Singh G, Sehrawat P. Fourth ventricle epidermoid tumor: Radiologic findings. Med J DY Patil Univ 2016;9:136-9
| Introduction|| |
Epidermoid cysts or tumors, known as pearly tumors or cholesteatomas, are uncommon benign lesions that may arise in the spine or intracranially, and the intracranial type accounts or <2% of intracranial tumors. , They usually occur in the cerebellopontine angle or in the parasellar regions. Epidermoid cysts of the fourth ventricle occur very rarely representing only 5-18% of all intracranial epidermoid cysts.  They arise from ectodermal inclusion during neural tube closure in the 3 rd to 5 th week of embryogenesis and have an extremely slow linear growth rate.  Because of their avascular nature and composition with cholesterol in a solid crystalline state and keratin within the tumor epidermoid tumors typically have long T1 and T2 relaxation times and have no enhancement on postcontrast MR images. 
| Case Report|| |
A 27-year-old male patient presented with complaints of gradually progressive intermittent headache associated with slurring of speech and gait imbalance on the left side since 6-7 months. No history of any seizures/major illness.
Magnetic resonance (MR) imaging of the brain was performed with a superconducting 1.5-T MR system (Siemens Model Magnetom Avanto 1.5 Tesla) with a standard head coil. The examination demonstrated a well-defined large lobulated mass lying within the fourth ventricle and is measuring 6.0 cm (transversely) 4.7 cm (anterioposteriorly) and 5.9 cm (cranio-caudally). The mass was causing expansion of the fourth ventricle and seen to compress the brainstem anteriorly and cerebellum posteriorly. Superiorly, it was seen extending into the aqueduct and displacing the quadrigeminal plate posterosuperiorly and caudally extending to the obex at the level of the foramen magnum. The mass was insinuating through the foramen of Magendie and the foramina of Luschka. It was also seen effacing the cisterna magna and bilateral cerebellopontine angle cisterns.
The mass appeared heterogeneously hypointense on T1-weighted images [Figure 1] and fluid-attenuated inversion recovery (FLAIR) [Figure 2], hyperintense on T2 weighted images [Figure 3]a-c] with restriction on diffusion-weighted images (DWI) [Figure 4]a and b]. Patchy areas of free diffusion were also seen centrally as well as peripherally within the lesion. No evidence of blooming on gradient sequence [Figure 5] was seen to suggest hemorrhage or calcification. No significant enhancement of the tumor was seen in images obtained after intravenous administration of gadolinium contrast material [Figure 6]a and b].
|Figure 1: T1-weighted sagittal image showing heterogeneously hypointense large lobulated mass lying within the fourth ventricle causing expansion of the fourth ventricle, compressing the brainstem anteriorly and cerebellum posteriorly|
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|Figure 2: Fluid-attenuated inversion recovery axial image showing heterogeneously hypointense within the fourth ventricle causing expansion of the fourth ventricle|
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|Figure 3: a-c(Axial, coronal and sagittal): T2-weighted images showing predominantly hyperintense lesion within the fourth ventricle extending into the aqueduct and displacing the quadrigeminal plate posterosuperiorly and caudally extending to the obex at the level of the foramen magnum. The mass is insinuating through the foramen of Magendie (b) and the foramina of Luschka (a)|
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|Figure 4: a and b: Diffusion-weighted images (DWI) and apparent diffusion coefficient (ADC) images showing patchy areas of restriction on DWI with corresponding low values on ADC images|
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|Figure 6: a and b: (Axial, sagittal): Postcontrast images showing no significant postcontrast enhancement|
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Dilatation of the lateral and the third ventricles was seen with ballooning suggesting obstructive hydrocephalus. Subtle periventricular ooze was also seen.
Sub-occipital craniotomy with subtotal excision was done. On histology, the cyst contained keratinized debris with a capsule consisting stratified squamous epithelium compatible with a fourth ventricle epidermoid cyst.
| Discussion|| |
Epidermoid cysts are congenital slow-growing benign tumors that constitute 0.2-1.8% of primary intracranial neoplasms. And the fourth ventricle epidermoid represents only 5-18% of all intracranial epidermoid cysts. ,, Epidermoid cysts were first described in 1807 by an artist in a French medical school,  and the first full description was given by the French pathologist Cruveilhier in 1829.  It is hypothesized that they form between the 3 rd to 5 th week of embryonic development due to displacement of the epithelial remnants that persist after the neural tube closure. , Acquired epidermoid tumors may develop as a result of trauma which is uncommon in the brain.
Grossly, epidermoid cysts are typically well-defined lesions with an irregular nodular outer surface and a shiny appearance hence known as pearly tumors.  Microscopically, are composed of an outer capsule of connective tissue that surrounds a layer of keratinized stratified squamous epithelium and inner cystic fluid that usually includes desquamated epithelial cells composed mainly of keratin in concentric layers and cholesterol in a solid crystalline state. ,
Most intracranial epidermoid tumors are intra-dural tumors. The most common intracranial location for epidermoid tumors is the cerebellopontine angle cistern, which accounts for approximately 40-50% of cases.  Although there are only a few cases of epidermoid tumor in the fourth ventricle, this location is the second most common for an epidermoid tumor in the posterior fossa.  Another common location is the sellar and parasellar region. Less common locations include intraparenchymal locations (epidermoid tumors have been reported in all lobes of the cerebral hemispheres), the pineal gland, the thalamus, and the septum pellucidum.  These tumors may also be seen intrinsically within the brainstem.  In rare cases, they have been reported in other locations such as the lateral ventricles.  Ten percent of epidermoid tumors are extradural, located in the skull or spine. 
The clinical manifestations of epidermoid tumors usually relate to the mass effect of the tumor on adjacent structures. Patients with a fourth ventricle epidermoid cyst usually present with a longstanding headache, vertigo, walking difficulties, and/or mental impairment. , Hydrocephalus is not commonly seen with intracranial epidermoid tumors, possibly due to fissuring of the cyst wall and the ability of cerebrospinal fluid (CSF) to decompress into the surrounding periventricular structures and outlet foramina.  However, our case showed features of obstructive hydrocephalus which was an uncommon finding.
At imaging, the classic appearance of an epidermoid tumor is that of a CSF-like mass insinuating into the cisterns and encasing adjacent vessels and neural structures.  On computed tomographic (CT) scans, the typical appearance is that of a nonenhancing and hypo-attenuating extra-axial mass. Calcifications may be seen within these tumors in 10-25% of cases. MR imaging is the best modality for evaluating these tumors. Characteristically, they are either isointense or slightly hyperintense relative to CSF on T1- and T2-weighted images.
Most of the epidermoids have a typical appearance however their signal intensity may vary depending on the amounts of cholesterol and keratin within the tumor.  These tumors may rarely appear hyper-attenuated on CT scans and show high signal intensity on T1-weighted images and low signal intensity on T2-weighted images due to high protein content therefore also referred to as white epidermoids. 
The major differential diagnosis for a fourth ventricle epidermoid cyst is arachnoid cyst, dermoid cyst, and cystic neoplasms. Arachnoid cysts are less lobulated and follow the signal intensity patterns of CSF with all MR pulse sequences including FLAIR and DWI.  Dermoid cysts are also lined by stratified squamous epithelium as epidermoid cysts. However, they also have epidermal appendages such as hair follicles, sweat, and sebaceous glands. On imaging appear they appear as well-defined low attenuating (fat density) lobulated masses on CT scan and typically show hyperintense signal on T1-weighted images.  Cystic neoplasms such as cystic medulloblastoma and cystic ependymoma have a heterogeneous appearance on imaging due to varying degree of hemorrhage, calcification, and necrosis. The solid component of these lesions may show restriction on DWI and often show heterogeneous contrast enhancement. 
Gross total resection of these tumors is the definitive treatment to prevent recurrence. The primary surgical objective is to decompress the mass by evacuating the cyst contents and removing nonadherent portions of the tumor capsule; portions of the capsule adherent to vital structures should be left undisturbed.  Rarely, there could be leakage of cyst contents into the subarachnoid space which leads to secondary chemical meningitis.  The reported rate of recurrence of epidermoid tumors in literature is highly variable. Postsurgery excellent functional prognosis is usually achieved. Malignant transformation of an epidermoid cyst into a squamous cell carcinoma may occur but is extremely rare. Malignant transformation should be suspected when there are progressive neurologic symptoms with rapid growth and contrast enhancement on serial images. , Very rarely, there may even be leptomeningeal tumor dissemination.  Therefore, special note should always be made when any enhancement is seen on images of these tumors. Although benign cystic tumors may show some degree of associated enhancement, it has been suggested that surgery should focus on the resection and histologic analysis of the enhancing area when encountered. 
| Conclusion|| |
Fourth ventricle epidermoid tumors are rare benign slow-growing tumors that usually manifest as insinuating masses that can be accurately diagnosed with MR imaging. Their MR signal intensity characteristics are usually similar or slightly hyperintense relative to CSF on T1- and T2-weighted images, but these tumors are not uniformly hypointense on FLAIR images as CSF and show restricted diffusion on DWI. Although most of the epidermoids do not enhance, minimal rim enhancement may be seen in up to 25% of cases, and more conspicuous enhancement may indicate malignant transformation.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]