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Neuroradiology Case of the Week

Case 92

Jennifer Nadeau and P-L Westesson MD, PhD, DDS

Clinical Presentation: A 56-year-old female presents with acute onset of headache and altered speech in December 2002. Patient was found to have a "pie in the sky" defect on the right consistent with a left-sided lesion. No significant contributory medical history

Radiological Findings:  The lesion is isointense to the brain on T1 and T2 and enhances intensely. It is a well-defined, nodular, intraventricular mass in the region of the trigone of the lateral ventricle.

Diagnosis: Atypical fibroblastic intraventricular meningioma

Discussion: Meningiomas are the most common nonglial primary brain tumor and the most common intracranial extra-axial neoplasm in adults. They account for approximately 15% of all intracranial neoplasms. The tumors arise from arachnoid cells of the tela choroidea or from cell rests within stroma of the choroids plexus.
     Intraventricular meningiomas without dural attachment is rare with an incidence of 0.5-3% of all intracranial meningiomas. 77.8% occur within the lateral ventricular trigone, 15.6% in the third ventricle and 6.6% in the fourth ventricle. These tumors are typically silent until they become large enough to block that portion of the ventricular system causing trapping and dilation of the more distal portions.
     Unenhanced and enhanced CT and MRI are the most accurate method of diagnosis. Meningiomas typically show increased density on CT scan, with smooth margins and are well circumscribed. Contrast enhancement is present and homogenous in most cases, but can be central or ring like due to the absence of a blood-brain barrier in meningioma capillaries. Hydrocephalus produced by lateral intraventricular meningiomas is typically localized to the ipsilateral trigone and temporal horn. On MRI, these tumors usually are hypo to isointense on T1-weighted images and iso- to hyperintense on T2 weighted images relative to cortex.
     Intraventricular meningiomas can show significant heterogeneity and extensive edema. It is therefore important to take into consideration the location of the lesion and the age of the patient when trying to differentiate from the more common choroids plexus papillomas. The papilloma is more commonly found in the lateral ventricle in children and in the fourth ventricle in adults. Further, papillomas typically have a magnitude of hydrocephalus out of proportion for the tumor size from CSF overproduction and tend to have irregular borders.
     The approach to treatment is surgical most often through a parietal temporal approach. Common objective for treatment is to minimize the occurrence of postoperative deficits related to the vicinity of visual, motor, or speech cortices as well as the optic radiations. Conformal radiation therapy can be used for residual tumor.

References:

1. Atlas MD, S. Magnetic Resonance Imaging of the Brain and Spine; 3rd Edition. Lippincott, Williams & Wilkins Co. Philadelphia: 2002; 723-725, 627, 631-632.
2. Couillard MD, P. et al. Microsurgical removal of an intraventricular meningioma with ultrasound guidance, and balloon dilation of operative corridors: case report and technical note. Surgical Neurology. 45(2):155-60, 1996 Feb.
3. Nakamura MD, M. et al. Intraventricular meningiomas: a review of 16 cases with reference to the literature. Surgical Neurology. 59(6):491-503; discussion 503-4, 2003 Jun.
4. Orrison MD, W. Neuroimaging. W.B. Saunders Co., Philadelphia: 2000; 637-638.