Choroid plexus papilloma is a rare, slow-growing, histologically benign intracranial neoplasm that is commonly located in the ventricular system. These tumors account for 0.4-0.6% of all intracranial neoplasms; in children (mean age, 5.2 yr), choroid plexus papillomas appear as large tumors and account for 1.5-6.4% of intracranial neoplasms. Papillomas are a surgically curable disease. In a study of 18 consecutive choroid plexus tumors, the mean age at presentation was 4.6 years. All patients underwent surgical resection. The survival rate was 100% for papillomas (mean follow-up for 73 mo). The survival rate of carcinomas was 50% (mean follow-up for 23.5 mo). Postoperative extraventricular drainage has been shown to be effective in lowering the rate of shunt requirement in these patients, probably through releasing the blood-tinged cerebrospinal fluid and small tumor-particle residue. [1, 2, 3, 4, 5, 6]
Computed tomography (CT) scanning and magnetic resonance imaging (MRI) are the investigative procedures of choice in the evaluation of choroid plexus papillomas. Because of the relatively noninvasive nature, ease, widespread availability, high reproducibility, and great contrast resolution of CT scanning and MRI, these examinations have supplanted all other methods of neuroimaging. With the addition of intravenously administered contrast material, the sensitivity of these imaging modalities approaches 100%. The multiplanar capability of MRI further aids in the characterization and localization of lesions. [7, 8, 9]
See the images below.
Although choroid plexus papillomas are readily apparent on most nonenhanced studies, the omission of enhanced imaging from the imaging protocol may result in incorrect conclusions about the tumor type and extent. In addition, misdiagnosis may result from an attempt to classify a choroid plexus tumor as benign or malignant solely on the basis of imaging characteristics.
Plain radiography is not used to investigate choroid plexus papillomas because of its low sensitivity and specificity; CT scanning and MRI are the imaging studies of choice.  However, evidence of increased intracranial pressure may be noted on plain films. The presence of faint intracranial calcification in appropriate locations, which is observed in 4.1% of patients, may suggest the diagnosis.
The advent of CT scanning has resulted in improvement in the detection and characterization of all intracranial masses, including choroid plexus papillomas. Choroid plexus papillomas appear as well-marginated round or lobulated solid masses and are isoattenuating or hyperattenuating relative to normal brain parenchyma on nonenhanced scans. In as many as 24% of patients, the tumors may contain foci of calcification, which is readily demonstrated on CT scans, compared with MRI. Choroid plexus papillomas are strongly enhancing after the intravenous administration of contrast material. 
In children, choroid plexus papillomas can be heterogeneous in appearance because of the accumulation of cerebrospinal fluid (CSF), blood, and blood products between the fronds and papillae. A heterogeneous appearance is a possible sign of malignancy. In adults, most choroid plexus papillomas are heterogeneous secondary to cystic and/or calcific degeneration. Associated findings include hydrocephalus, which may involve the lateral, third, and fourth ventricles to varying degrees. [12, 13]
The presence of irregular margins should raise concerns about malignancy. Choroid plexus papillomas may have limited parenchymal invasion, which makes the distinction of the benign tumor from its malignant counterpart difficult.
Ossification in choroid plexus papillomas does not occur, although it has recently been described in one case of a papilloma within the fourth ventricle in a 21-year-old man. 
Magnetic Resonance Imaging
MRI the test of choice for the diagnosis of choroid plexus papilloma for several reasons. [15, 16] Multiplanar imaging, which is possible with MRI, can be used to precisely localize and determine the extent of the choroid plexus papilloma and thereby aid in surgical planning. MRI also has the advantage of eliminating artifacts of the posterior fossa, which can occasionally be problematic with CT scanning. In addition, MRI easily depicts local parenchymal invasion, which is occasionally present, and may be useful in distinguishing benign tumors from more aggressive or malignant choroid plexus tumors.
Choroid plexus papillomas can occasionally be bilateral or multiple, and interventricular extension, an ancillary diagnostic sign of choroid plexus papilloma, is readily identified in the coronal plane. This sign is not described with other interventricular tumors. Although uncommon, interventricular extension through the foramen of Munro, cerebral aqueduct, or foramen of Luschka or Magendie is also helpful diagnostic sign (see the following image). 
Multifocal concomitant choroid plexus papillomas are rare. These may occur secondary to biologic seeding of cerebrospinal fluid from a primary papilloma or mere coincidental tumor occurrence. 
Choroid plexus papillomas appear as heterogeneous masses, with or without cystic components; these may have intratumoral signal voids that correspond to a rich vascular supply or low-intensity areas that correspond to calcifications. On T1-weighted images, choroid plexus papillomas are slightly hypointense relative to gray matter in adults (see the images below). In children, the masses are isointense. Small areas of high signal intensity are compatible with localized hemorrhagic components.
On T2-weighted images, tumors in both adults and children have high signal intensity, which may approximate the signal intensity of CSF. After the injection of a paramagnetic contrast agent such as gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA), intense enhancement is observed. 
The superior imaging capability of MRI in the examination of the spinal canal may reveal evidence of seeding to the spinal subarachnoid space on rare occasions, particularly with posterior fossa tumors.
Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see Nephrogenic Fibrosing Dermopathy. NSF/NFD has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see FDA Information on Gadolinium-Based Contrast Agents or Medscape.
Ultrasonography may be useful in special circumstances, such as in neonates.  The availability, portability, accuracy, low cost, and lack of a requirement for sedation make ultrasonography a valuable tool. In many instances, ultrasonography is the examination of choice for initial screening. Ultrasonographic evaluation may also be valuable in the postoperative assessment of the neonatal brain.
In cases of choroid plexus papilloma, real-time ultrasonography demonstrates the presence of hydrocephalus. The tumors themselves appear as heterogeneous, highly echogenic intraventricular masses with irregular borders. Doppler ultrasonographic studies have shown pulsatile intratumoral vascular channels with biphasic flow. Occasionally, intratumoral cysts are identified; these appear as hypoechoic areas and are believed to represent areas of hydropic degeneration.
The blood supply to choroid plexus papillomas is derived from the choroid plexus. An enlarged anterior choroidal artery supplies tumors within the temporal horns of the lateral ventricles, whereas the posterior choroidal arteries supply masses in the atria or posterior horn. Branches of the posterior inferior cerebellar artery may supply tumors in the fourth ventricle.
Angiographic signs of choroid plexus papillomas may include the presence of many small spiral arteries; a meningioma-type blush with early tumoral circulation and persistent enhancement into the venous phase; displacement of vessels such as the internal cerebral veins; and evidence of ventricular dilatation.