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Neuroradiology Case of the Week

Case 114

Clinical Presentation: The patient is an 18-year-old female who presented with visual changes in her left eye, headache, and fatigue. Her symptoms were originally thought to be due to a sinus infection, but after a neurophthalmologist found left eye retinal hemorrhage, it was recommended that she have MR studies of the head.

Radiological Findings: MRI of the brain shows a large mass measuring about 5.3 x 5.1 x 5.0 cm in the atrium of the left lateral ventricle. There is heterogeneous T1 isointensity and T2 and FLAIR hyperintensity with homogenous contrast enhancement. There are a few small areas of T1 hyperintensity at the posterior, inferior, and lateral margins of the lesion indicating hemorrhage. There is evidence for CSF outflow obstruction with dilation of the temporal horn of the left lateral ventricle. The rest of the supratentorial ventricular system is normal. There is minimal mass effect and no midline shift. Diffusion weighted images do not show any restricted diffusion.
     MR spectroscopy shows a nonvisualized peak of NAA with a markedly increased choline peak. These features are suggestive of intraventricular meningioma, choroid plexus papilloma or carcinoma, as well as subependymoma.

Diagnosis: Choroid plexus carcinoma

Discussion: Choroid plexus tumors (CPT) are rare tumors that arise from the intraventricular neuroepithelial tissue responsible for the production of CSF. Eighty percent are the benign choroid plexus papilloma (CPP) of WHO grade I, while the other 20% are the malignant choroid plexus carcinoma (CPC) of WHO grade III. Both types, but especially the carcinoma, are common in children, though adults may also be affected. They account for 0.4-0.6% of all brain tumors, 2-4% of all pediatric brain tumors, and 10-20% of brain tumors in those less than one year of age.
     Fifty percent of all choroid plexus tumors are found in the lateral ventricles, 40% in the fourth ventricle, 5% in the third ventricle, and 5% in multiple sites. Additionally, CPT may be found in extraventricular locations such as the cerebellopontine angle, the supracellar region, the frontal lobe, and posterior commissure, the pineal gland, and the cerebellum. Tumors of the lateral ventricle are more common in individuals less than 10 years of age, whereas tumors in the fourth ventricle and cerebellopontine angle are more common in individuals between 0-50 years of age. Location does not vary with histology.
     Choroid plexus papilloma is the most common brain tumor in children less than one year of age and usually presents with macrocrania, bulging fontanelles, vomiting, headache, and ataxia. Diffuse hydrocephalus often occurs due to overproduction of CSF, impaired absorption, and mechanical obstruction. Gross pathology reveals CPP to be a well-circumscribed, lobulated, pink intraventricular mass with a cauliflower-like appearance that may be invaginated into the brain parenchyma. Microscopy typically shows absence of mitotic activity, necrosis, and brain invasion. Immunohistochemical characteristics include expression of S-100 protein in 90% of CPP, as well as expression of cytokeratin and vimentin. CPP is a benign, slow-growing tumor that may seed the CSF pathways; nevertheless, with total surgical resection, 5-year survival is about 100%.
      Choroid plexus carcinoma is a malignant tumor that presents with nausea, vomiting, headache, and obtundation. In contrast with CPP, CPC can produce focal neurologic signs and symptoms. There may be hydrocephalus due to overproduction of CSF, decreased absorption, and mechanical obstruction. Of note, though, is that there is usually less overproduction of CSF from carcinoma than from papilloma. Eighty percent of CPC arise in children, usually within the first 5 years of life and with equal male/female distribution. Gross pathology reveals a lobulated, intraventricular mass, which is similar to the gross appearance of CPP. Microscopy helps differentiate CPC from CPP in that carcinoma is hypercellular, pleomorphic, with increased mitotic activity, cysts, necrosis, hemorrhage, microcalcifications, and brain invasion. Immunohistochemical characteristics include expression of cytokeritan, but minimal expression of glial fibrillary acid protein, transthyretin, and S100. CPC is a rapidly growing tumor that may seed the CSF pathways. Prognosis is poor with only 40% surviving at 5 years. Treatment is total surgical resection with adjuvant therapy, specifically radiotherapy for adults and chemotherapy for children.
     It is usually not possible to distinguish CPP from CPC with imaging studies as the two types of tumors have similar characteristics. Therefore, tissue biopsy is required in order to make a definitive diagnosis. Nevertheless, one distinguishing feature is that CPC is generally a more heterogeneous lesion.
     On CT, both CPP and CPC appear as iso- or hyperattenuated intraventricular masses. On MR TI-weighted images, both lesions are iso- to hypointense. On MR T2-weighted images, both lesions may be of mixed intensity, either iso-, hypo-, or hyperintense. Contrast enhancement on both CT and MRI shows CPP to have homogenous enhancement and CPC to have heterogeneous enhancement. PET scan with 11C-Methionine shows increased tumor-to-normal brain ratios in CPP and CPC. Additionally, Tc-99m Sestamibi is increased in both lesions.

References:

1. Koeller KK, Sandberg GD. From the Archives of the AFIP: Cerebral intraventricular neoplasms: radiologic-pathologic correlation. Radiographics. 2002; 22:1473-1505. [Medline]
2. Osborn: Diagnostic Imaging: Brain. 2004 Amirsys: I:6-60 - I:6-64
3. Wolff J, Sajedi M, Brant R, Coppes MJ, Egeler RM. Choroid plexus tumours. British Journal of Cancer. 2002; 87:1086-1091. [Medline]
4. Meyers SP, Khademian ZP, Chuang SH, Pollack IF, Korones DN, Zimmerman RA. Choroid plexus carcinomas in children: MRI features and patient outcomes. Neuroradiology. 2004 Aug 12 [Epub ahead of print].