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Choroid Plexus Tumors

Introduction

Choroid Plexus Tumors (CPTs) are rare lesions of the central nervous system. CPTs were first described by Guerard (1883), and were found in the literature usually as case reports until the midpart of this century when large series of cases were reported (1). They can be divided in Choroid Plexus Papilloma (CPP) and Choroid Plexus Carcinoma (CPC). These tumors have a fascinating biology that has interested generations of neurosurgeons. CPTs are easily recognized as neoplastic derivates of the normal choroid plexus, and reported to be from 0.5 to 0.6 per cent of all brain tumors. Greenberg (2) in a serie of 73 patients with intraventricular tumors identified 4 cases (5%) of CPP, and 2 cases (2.5%) of CPC ( graphic 01). CPTs have an incidence rate between 1,5% to 3,9% in the general pediatric population, with a high incidence in children less than 2 years old. Ellenberg et al (3) reported a serie of 40 patients operated on because of CPTs, and 65% of then were younger than two years old. CPCs constitute 29 to 39 per cent of all CPTs. The sex distribution seems to be equal. There are no racial, ethnic or geographic which can be implicated in either the incidence or etiology of CPTs.

Clinical Features

Intracranial Hypertension is the most commom presentation of CPT. Increased intracranial pressure is usually caused by ventriculomegaly from obstructive hydrocephalus or over production of cerebrospinal fluid. Because the majority of cases occur in infants and young children, there are characteristic features of raised intra-cranial pressure. The more commom symptoms are nausea, vomiting, irritability, headache, visual disturbance and seizure. The most commom accompanying signs were craniomegaly, papilledema, and decreased level of consciousness.

In children less than 2 years of age, craniomegaly secondary to hydrocephalus is the most commom physical finding. After this age, in both children and adults, ataxia, papilledema and extraocular motility dysfunction (including sunsetting of eyes) are the usual presentation signs. Cranial nerve involvement can include II through X in varying combinations. Other physical features of CPTS include hemiparesis, sensory and reflex changes, cerebellar dysfunction, and nystagmus. The hydrochepalus with CPTs is unique among all central nervous system tumors as it is caused not only by obstruction of flow, but also by cerebrospinal fluid overproduction from the tumor itself. CPT are viewed as slow-growing tumors, then presence of stupor or coma suggest an acute deterioration.

Delfini and cols.(4) reported the clinical presentation of 33 patients with CPPs, see table one :

In patients with CPTs, computed tomography (CT) scanning is frequently the initial diagnostic test obtained on non-enhanced study ( Figs. 1 and 2 ). The most commom location of CPTs, up to 75% of cases, is the lateral part of the third ventricle ( atrium ). The tumor appears as a smooth or lobulated mass homogeneous in texture, which is isodence to slightly hiperdense in relation to surrounding brain parenchyma. This increase in attenuation is due to highly vascular nature of these tumors, and their location adjacent to hypodence intravenous contrast, there is marked, homogeneous enhancement.

There are some differences between CPP and CPC on CT scan. A CPC will appear as an inhomogeneous mass on both contrast and non-contrast CT scans, but may be densely contrast enhance. CPC are iso to hiperdense in relation to surrounding parenchyma and CT will show evidence of local brain invasion. An additional finding with a imaging in CPTs is the presence of calcifications in up to 80% of cases. The normal choroid plexus is not calcified in adults, especially in the lateral ventricle. A calcified tumor in childhood localized to the ventricular system and associated with hydrocephalus should suggest the presence of CPT. Similarly, calcified tumor in the third and fourth ventricles, in adults, may indicate a CPT. The differential diagnosis of a calcified ventricular tumor includes ependymoma, astrocytoma, meningioma, teratoma, pineal region tumors and craniopharyngioma. The CPP has a stippled, punctate pattern of calcification on CT, with the calcium in a CPC having more of a globular appearance.

Magnetic resonance imaging ( MRI ) discloses vividly the anatomy, demonstrating the characteristic molding of tumor within the ventricle. The sagital and coronal views may show the characteristic egress of tumor through ventricular outlets. For CPPS, nonhomogeneity of signal noted on unenhaced T1 and T2-weighet images has been clotted to vascularity, calcification or old hemorrhage. Gadolinium infusion produces intense enhancement. The vascular supply is identified by an angiographic study. The vascular supply may be anterior choroidal, posterior choroidal or lateral striate vessels. The MRI findings in CPCs are similar to those found with CT. These tumors are again of intermediate signal intensity, but are inhomogeneous in character in T1, T2 and proton density weighted sequences. Areas of low signal intensity on T1 weighting, and a high signal intensity on T2 weighting in the center of the tumor have been found histologically to be consistent with necrosis.

Rovit et al (5) reported that the site at which CPPs occured in order of frequency, guided by imagens, were lateral ventricle (43%), fourth ventricle (39%), third ventricle (10%), and cerebellopontine angle (9%). CPPs arising from the cerebellopontine angle should be considered in the differential diagnosis of such tumors as acoustic neuroma, meningioma, neurinoma of Vth or VIIth nerve, glomus jugulare tumor, dermoid and epidermoid cyst (6).

Pathology

The gross appearance of CPP is frequently described as cauliflower-like. Indeed papillomas are seem as exaggerations of the soft pronds of normal choroid plexus that are found in the ventricles. Their shade is roughly globular with an irregular surface and intervening encapsulated areas. Old hemorrhage can be noticed on occasion. The papillomas tend to expand the ventricular rather than transverse the ependyma and invade adjacent brain. Nevertheless, the proximity of these tumors to deep-shorted structures such as the internal cerebral veins and limbic system can make their removal problematical. Microscopic CPP also recapitulate the histological features of the normal choroid plexus.

Papillae are numerous and are covered with a simple cuboidal or columnar epithelium. The stroma of these fibrovascular structures is composed of connective tissue and small blood vessels. The presence of the connective tissue stroma is notable manly because it serves as a feature that allows the investigators to distinguish between CPP and papillary forms of ependymoma. CPCs are diagnosed on the basis of their microscopic appearance. The major features by which these carcinomas are diagnosed include brain invasion, cytological atypia, increased mitotic activity, and necrosis (7). Immunohistochemical staining usually reveals cytokeratin and S-100 positively in CPTs. There may also be glial fibrillary acidic wide spread. CPC may be positive for carcinoembryonic antigen. More recently, attention has been focused on thransthyretin, which is immunohistochemical localized to the choroid and is thought to be a specific marker for CPTs. Various others antibodies can be used : epithelial membrane antigen, tumor polypeptide antigen, pre-albumin, vimentin and lecitin links.

Treatment

Because most patients present with symptoms of intracranial hypertension, patient management is directed toward relieving hydrocephalus, determining the histopathological diagnosis of the mass lesion, and removing the tumor. Unless the patient is rapidly deteriorating, urgent drainage of the cerebrospinal fluid is not necessary. At the time of surgery, a ventricular drain is usually placed first in order to reduce brain tension and allow sufficient brain retraction. In the young child or infant, it may be prudent to leave a ventricular drain in situ postoperatively for several days to monitor the intracranial pressure and to determine whether shunting of the fluid is required.

In addition to some of the complications associated with intraventricular surgery, such as injury to the deep venous drainage system, the fornices, or the thalamus, the surgery of choroid plexus tumors may be potential hazardous because of their extreme vascularity. The best surgical approach, at least for CPPs , is to identify and expose the vascular pedicle, so as to perform an en bloc excision or the tumor.

Lateral ventricular papillomas are best approached through a temporo-parietal flap that provides access to the temporal pole and the angular gyrus posteriorly. Before opening of the dura, any cerebrospinal fluid trapped in the lateral ventricle can be drained to decompress the brain. A direct cerebrotomy posterior to the angular gyrus allows access to the entire trigone and permits the pedicle of the tumor to be identified and coagulated. In the pedicle and the tumor extend anteriorly to the region of the foramen of Monro, a widen exposure is necessary. To this end, and incision can be more in the frontal convolutions, with the lateral ventricle approached from an anterolateral direction. The blood supply from choroidal vessels is posteroinferior to the bulk of the tumor and therefore hidden from the direct view of the surgeon in this approach. Alternatively, lateral ventricular tumors may be approached through a cerebrotomy through the superior and middle temporal gyri.

Third ventricular tumors are rare and are approached by a midline transcallosal route. The anterior aspect of the ventricle is entered through a generous opening in the corpus callosum extending from the rostrum to the supraoptic recess. In this way, the tumor can be separated from the choroid of the tela choroidea, to which it is usually attached, and the accompanyng bridging vessels can be identified and divided.

In general, the rationale for treatment of CPCs parallels that for CPPs. However, with CPCs, the problems with tumor vascularity are accentuated, as are the difficulties between the tumor and the brain. Compounding these difficulties is the excessive friability of the carcinoma. For these reasons, the combination of chemotherapy ( using isofosfamide, carboplatin and etoposide ) after guided biopsy treatment is helpful in improving the prognosis. Chemotherapy is not curative but it does cause a reduction in tumor volume and, more importantly, has tended to reduce the tumor vascularity. This allows for a second stage of operation which is more safely performed and typically allows for more complete removal (8).

The role of radiation therapy in the treatment of CPPs remains undefined. Radiation therapy probably is best reserved for recurrent disease after the most complete surgical resection possible.

References

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