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Neuroradiology Case of the Week

   Case 62

Karin Westesson and P-L Westesson MD, PhD, DDS

Clinical Presentation: A 10-month-old female presented with a seven month history of seizures. MR imaging and MR spectroscopy of the head was obtained to evaluate for an intracranial mass lesion.

Radiological Findings: There was a well-defined enhancing 1.8 cm mass lesion between the anterior horns of the lateral ventricles at the region of the foramen of Monro. It was predominantly isodense on T2 and T1 and homogeneously enhanced following Gadolinium. The MR spectroscopy within the enhancing lesion showed a depressed NAA peak with relative elevation of the choline peak. There was slight elevation of the myoinositol peak.

Diagnosis: Choroid plexus papilloma

Discussion:  Choroid plexus papillomas are irregular lobulated tumors that arise from the epithelium of the choroid plexus and extend into the cavity of the ventricles [1,2]. It affects mostly children from infancy to 5 years of age, mainly in the 1st year of life and shows dominance in males. The papillomas are often located in the trigone area of the lateral ventricles. In children, most originate in the left lateral ventricle, whereas in adults the most common origin is the 4th ventricle and in the cerebellopontine angle [2]. The tumors are well-marginated and separated from the brain and are more sharply defined than ependymomas. They are detached from the petrous bone unlike schwannomas and meningiomas [3]. Cystic areas and small hemorrhages are common. The primary symptom is severe hydrocephalus caused by an overproduction of CSF or a blockage in the subarachnoid cisterns [1].
   Choroid plexus papillomas have distinct imaging characteristics which reduces the number of differential diagnoses. The main differential factor is that of malignant degeneration to a choroid carcinoma or an ependymoma. Choroid plexus carcinomas are more common in children, whereas in adults the differentiation of a choroid plexus carcinoma from a metastatic carcinoma may be difficult. Occasionally, these tumors can be confused with colloid cysts, although the latter lesions have much different imaging characteristics as discussed previously. Location is also used to eliminate differential diagnoses. A colloid cyst is typically located in the Foramen of Monro or in the 3rd ventricle. A meningioma is located in the trigone of the lateral ventricle. Ependymomas, neurocytomas and metastases are found in the lateral ventricles [4].
   On CT scan, papillomas appear lobulated, isodense to mildly hyperdense with occasional punctuate foci of calcification and they enhance intensely and homogeneously. On MR, papillomas are iso- to hypointense to grey matter on T1 [4]. On T2 weighted images, the papillomas are heterogeneously hyperdense due to the presence of iron in the hemorrhagic areas and will moderately enhance depending on the degree of calcification, vascular and cystic characteristics [1].
Choroid plexus papillomas are generally surgically treated and the 5-year survival rate is 100% [4].

References:

1. Atlas SW, Lavi E, Goldberg HI. Extraaxial brain tumors. Magnetic Resonance Imaging of the Brain and Spine, 3rd ed. Ed. Scott W. Atlas. Philadelphia: Lippincott, Williams, Wilkins, 2002; 764-770.
2. Barkovich, AJ. Pediatric Neuroimaging. 3rd ed. Philadelphia: Lippincott, Williams Wilkins, 2000.
3. Maya MM, Lo WWM, Kovanlikaya I. Temporal bone tumors and cerebellopantine angle lesions. Head and Neck Imaging, 4th ed. Eds. Peter M. Som and Hugh D. Curtain. St. Louis: Mosby, 2003; 1306, 1307.
4. Osborn AG, Blaser SI, Salzman KL. Pocket Radiologist: Brain. Philadelphia: W. B. Saunders, 2002.