INTRODUCTION	Section 2 of 11
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Background: Choroid plexus papilloma (CPP) is a rare, slow-growing, histologically benign intracranial neoplasm that is commonly located in the ventricular system.

Pathophysiology: On gross pathologic examination, CPPs appear as lobulated encapsulated masses. They are neuroectodermal in origin and similar in structure to a normal choroid plexus. They arise from epithelial cells of the choroid plexus arranged as a multitude of papillary fronds resting on a delicate stroma of fibrovascular connective tissue. CPPs often are associated with a vascular stalk connected to the choroid plexus, allowing mobility within the ventricular system.

Blood breakdown products and high protein secretion result in hydrocephalus because of obstruction of cerebrospinal fluid (CSF) absorption at the level of the arachnoid granulations. CSF is produced at 4-5 times the normal rate, with resultant communicating hydrocephalus. Hydrocephalus also may result from direct tumor obstruction of the outlet of CSF flow from the ventricular system; this finding is especially true for tumors in the third ventricle, with resultant CSF outflow obstruction at the foramina of Monro.

Bone formation and neuromelanin production may occur, but these are extremely rare. Doran et al and Reimund et al, describe only 6 cases of bone formation and 2 cases of neuromelanin production, respectively.

CPPs are not malignant; however, malignant evolution may occur, with an incidence of 10-30%. The lateral ventricles are the most common sites for malignant degeneration. With a clinical and histologic pattern of malignancy, which is characterized by invasion, mitotic figures, nuclear pleomorphism, necrosis, and metastasis, these tumors are classified as carcinomas.

Frequency:

• Internationally: Papillomas of the choroid plexus are rare, accounting for 0.4-0.6% of all intracranial neoplasms. In children, CPPs account for 1.5-6.4% of intracranial neoplasms.

Mortality/Morbidity: The disease burden can be significant, especially in young children. Morbidity is associated with developmental delay in 39% of pediatric patients, severe behavioral problems in 17%, and epilepsy in 48%.

In a recent series by McEvoy et al, the 5-year survival rate was 100%. In a review by McGirr et al, tumors did not recur in half of the patients who underwent subtotal resection. Radiation therapy after surgical intervention usually is reserved for the treatment of choroid plexus carcinoma.

If the tumor evolves into malignancy, the prognosis is dismal, with a 5-year survival rate of 26%. However, the histologic appearance may not be predictive of biologic behavior because some highly anaplastic choroid plexus tumors can be clinically benign, whereas some histologically inactive tumors are invasive.

The presence of mitotic figures, although rare in CPP, may be predictive of the likelihood of both recurrence and malignant evolution. Such histologic findings in the surgical specimen should result in close clinical follow-up care of patients, especially in those whose postoperative images show findings of residual tumor.

Race: No racial predilection is reported.

Sex: The male-to-female ratio is 2.8:1, as Sarkar et al reported in a review of 23 cases.

Age: Most CPPs appear as large tumors in young individuals. They are more common in children than in adults, with a mean patient age of 5.2 years. Of all CPPs, 20% occur in patients younger than 1 year, and 85% occur in those younger than 10 years. CPPs may be discovered at birth. They account for approximately 40% of pediatric tumors that are present within the patient's first 60 days of life.

Anatomy: CPP may arise wherever a choroid plexus exists. In all age groups, the sites at which CPPs occur, in order of frequency, are the lateral ventricles (43%), fourth ventricle (39%), third ventricle (10%), and cerebellopontine angle (8%).

Tumoral distribution varies between pediatric and adult patients. In children, most CPPs (80%) are located in the lateral ventricles. McEvoy et al describe no predilection for the left or right side, while others, such as Hopper et al, report an increased incidence of tumors in the left lateral ventricle. About 16% of papillomas are found in the fourth ventricle, and 4% are found in the third ventricle. In those aged 0-10 years, the relative incidence of third ventricular papillomas approaches 30%. The fourth ventricle is the most common location of CPPs in adults.

CPPs occasionally can be bilateral or multiple. Interventricular extension can occur with a CPP; this sign is not described with other interventricular tumors. Although uncommon, interventricular extension through the foramen of Munro, cerebral aqueduct, or foramen of Luschka of Magendie is a helpful diagnostic sign.

CPPs can arise in the cerebellopontine angle, secondary to direct extension from tufts of choroid protruding through the foramen of Luschka. Extension into the foramen magnum may occur, with possible brainstem compression. Seeding can occur throughout the cerebrospinal axis; this usually results in a solitary metastasis from a lateral ventricular tumor in a child and in subarachnoid seeding to the spine from a fourth ventricular lesion in an adult. On rare occasions, widespread metastases from benign papillomas are observed.

A few dozen cases of papillomas of a nonventricular origin are reported. These are possibly explained by an origin in the embryonic rests of choroid plexus.

Extraventricular spread to the brain parenchyma, pineal region, or suprasellar area, as well as drop metastasis, is observed on occasion. Bone invasion may rarely occur; most commonly, this involves the petrous bone. Usually, involvement of bony structures implies the presence of choroid plexus carcinoma or malignant transformation of a benign papilloma. Carpenter et al describe single case reports of extension to the cavernous sinus and invagination into the jugular foramen.

Clinical Details:

Signs and symptoms

In a recent review of 25 cases by McEvoy et al, the median duration of symptoms was 1 month, and approximately one third of patients presented within 2 weeks.

The tumor's presence often is heralded by nonspecific signs and symptoms of increased intracranial pressure, which is present in 91% of patients, frequently in association with obstructive hydrocephalus. Vomiting is the most common sign in children. The presentation can also include hemiparesis, homonymous visual field defects, and generalized tonic/clonic and focal seizures. When the neoplasm arises within the cerebellopontine angle, the presentation usually involves ataxia and cranial nerve palsy, most commonly that of cranial nerves V, VII, or VIII. In adults, headache is the most common presenting symptom; this finding may be related to an alteration in head position.

Grodin et al report a case of sudden death in which the tumor involved the third ventricle, causing acute ventricular obstruction.

Consider CCP when an expansile, calcified, and vascular mass is closely associated with the ventricular system or cerebellopontine angle, especially in the presence of nonobstructive hydrocephalus.

Surgical treatment

As a result of their benign nature and slow growth, CPPs are amenable to complete surgical excision, with an expectation of total cure. Not surprisingly, a favorable long-term outcome is expected; the goals are a cure for all children and no requirement for adjuvant therapy. These goals are especially achievable if surgery can be performed early, before hydrocephalus or spontaneous hemorrhage cause irreversible damage.

Despite advances in modern surgical techniques, such as the use of surgical microscopes, bipolar coagulation, stereotaxy, and image-guidance techniques, a significant risk of mortality and morbidity may be associated with surgical treatment.

Although the details are beyond the scope of this article, extreme tumor vascularity, which is often present, may hinder complete resection. The perioperative management of hydrocephalus, which is common in patients with CPP, is controversial; especially controversial are the timing or necessity for shunt creation. Subdural fluid collections, frequently caused by the persistence of a ventriculosubdural fistula, are often found in the postoperative period; occasionally, these can cause symptoms of increased intracranial pressure.

Preferred Examination: CT and MRI are the investigative procedures of choice in the evaluation of CPPs. Because of the relatively noninvasive nature, ease, widespread availability, and high reproducibility, and great contrast resolution of CT and MRI, these examinations have supplanted all other methods of neuroimaging.