Choroid Plexus Tumors: Understanding Your Pathology Report

Section Editor: Anthea Girdwood MD FRCPC
September 10, 2026

Choroid plexus tumors grow from the choroid plexus, the tissue inside the brain that makes the fluid surrounding the brain and spinal cord. There are three types, and the pathology report will name one: choroid plexus papilloma, atypical choroid plexus papilloma, and choroid plexus carcinoma. They range from a slow-growing tumor that is usually cured by surgery alone to a cancer that needs further treatment.

These tumors are uncommon, making up roughly 1 to 4 percent of brain tumors in children. They are much more common in the very young, accounting for as many as 10 to 20 percent of brain tumors diagnosed in the first year of life. This article is written for parents and caregivers. It explains what appears on the pathology report, how the three types differ, and why a diagnosis of choroid plexus carcinoma leads to a genetic test for the whole family.

What is the choroid plexus?

The brain contains four connected fluid-filled spaces called ventricles. Lining parts of them is a frilly tissue called the choroid plexus, which produces cerebrospinal fluid. That fluid circulates the brain and spinal cord, cushioning them and carrying away waste.

The choroid plexus is built from a single layer of cells sitting on delicate fronds of tissue carrying blood vessels. A choroid plexus tumor keeps that frond-like architecture, which is why it is recognizable under the microscope and why the pathology report may use the word papillae to describe it.

Because these tumors sit inside the ventricles, they cause problems in two ways. They block the normal flow of cerebrospinal fluid, and some of them produce extra fluid themselves. Both lead to a build-up of pressure inside the head, called hydrocephalus, which is what usually brings a child to medical attention.

What are the symptoms of a choroid plexus tumor?

Almost all the symptoms of a choroid plexus tumor come from the build-up of fluid and pressure rather than from the tumor itself. What a family notices depends heavily on the child’s age.

In babies. A head that is growing faster than expected, a bulging soft spot, vomiting, unusual sleepiness or irritability, poor feeding, and eyes that appear to look downward.
In older children. Headaches that are worse in the morning or on waking, vomiting, blurred or double vision, unsteadiness, and changes in behavior or school performance.
Seizures. Less common, and more likely with tumors in the lateral ventricles.

Because a baby’s skull can still expand, the head circumference measured at routine checks is often the first sign that something is wrong.

How is the diagnosis made?

A choroid plexus tumor is usually first seen on imaging. An MRI shows a lobulated mass inside a ventricle that lights up strongly with contrast. The appearance is often characteristic enough that doctors suspect the tumor type before surgery.

A pathologist confirms the diagnosis by examining tissue. Unlike many brain tumors, a needle biopsy is usually not the first step. These tumors have a rich blood supply and bleed readily. The neurosurgeon therefore aims to remove the whole tumor in one operation, both to treat it and to obtain the tissue. The pathology report is therefore based on the removed tumor rather than on a small sample.

Under the microscope, the tumor consists of fronds of tissue, each with a core containing blood vessels and covered by a layer of cells. In a papilloma, these cells look orderly and closely resemble the normal choroid plexus. As the tumor becomes more abnormal, the cells crowd together, the frond pattern breaks down into solid sheets, and dead tissue appears.

Choroid plexus papilloma, atypical papilloma, and carcinoma

Choroid plexus tumors are divided into three types by how the cells look and how quickly they divide. Each is assigned a grade under the World Health Organization classification of central nervous system tumors, 5th edition, published in 2021. The grade is the most useful piece of information on the report for understanding what happens next.

Choroid plexus papilloma, WHO grade 1. The commonest of the three and the most favorable. The cells closely resemble normal choroid plexus, and dividing cells, called mitotic figures, are rare. Complete surgical removal usually cures it, and most children need no further treatment.
Atypical choroid plexus papilloma, WHO grade 2. Defined by a single feature: more dividing cells than a papilloma, specifically two or more mitotic figures in a defined area of tissue. Everything else may look like a papilloma. It has a higher chance of recurrence, particularly in children over 3 and in adults, so follow-up is closer.
Choroid plexus carcinoma, WHO grade 3. A cancer. The diagnosis requires several abnormal features together. These include frequent mitotic figures, crowded cells, and cells varying widely in size and shape. The frond pattern is also lost in favor of solid sheets, and necrosis (dead tumor tissue) is present. Invasion into the surrounding brain may also be described. Surgery alone is not sufficient, and chemotherapy is part of treatment.

Most choroid plexus carcinomas occur in children under 3. Papillomas occur across all ages, including adults, and usually arise in the fourth ventricle rather than the lateral ventricles.

Immunohistochemistry and molecular testing

Additional tests are performed on the tumor tissue for two reasons. They confirm that the tumor really comes from the choroid plexus, and they separate it from other tumors that can look similar.

Immunohistochemistry uses antibodies to detect specific proteins in the tumor cells. Choroid plexus tumors are typically positive for cytokeratins, and for proteins found in normal choroid plexus such as transthyretin, Kir7.1, and stanniocalcin-1. The last two are the most specific and often settle the question.

One further stain matters a great deal. Rhabdoid tumors of the brain, called atypical teratoid/rhabdoid tumors, can closely mimic a choroid plexus carcinoma in a young child. They are separated by a stain called INI1, also written SMARCB1. Choroid plexus tumors keep this protein, and rhabdoid tumors lose it. Loss of INI1 changes the diagnosis entirely, so this stain is performed whenever a carcinoma is considered in an infant.

Many centers now also run DNA methylation profiling, which reads chemical marks on the tumor’s DNA and compares the pattern against thousands of known tumors. It is most useful for atypical papillomas, where the appearance alone can be difficult to interpret, and it adds information about how the tumor is likely to behave.

TP53 and Li-Fraumeni syndrome

This section applies mainly to choroid plexus carcinoma, and it has the widest consequences.

TP53 is a tumor suppressor gene whose normal job is to detect damaged DNA and stop the cell from dividing. Roughly half of choroid plexus carcinomas carry a change in this gene. In a substantial share of those children, the change is not confined to the tumor but is present in every cell of the body, having been there from birth. That situation is called Li-Fraumeni syndrome, an inherited condition that raises the lifetime risk of several cancers.

Genetic testing on blood or saliva is recommended for every child diagnosed with a choroid plexus carcinoma, whether or not anyone else in the family has had cancer. Estimates of how often a germline TP53 change is found in this group range from about 50 to 80 percent, which is among the highest of any single diagnosis. International guidelines list choroid plexus carcinoma as an indication for TP53 testing in its own right, precisely because so many affected children have no family history at all.

The result changes three things.

Treatment. Children with a germline TP53 change are unusually sensitive to the long-term effects of radiation, with a high risk of new cancers appearing later within the treated area. Where a germline change is found, teams generally avoid radiation and place more weight on complete surgical removal and chemotherapy.
Follow-up for the child. Lifelong surveillance for other cancers is offered, using regular imaging and examinations.
The family. Parents, brothers, and sisters may be offered testing, and those who carry the change are offered the same surveillance.

Papillomas and atypical papillomas are much less often linked to TP53, and testing is not automatic. Your child’s team will explain whether it applies.

How much of the tumor was removed

How completely the tumor was taken out is the strongest single predictor of outcome for all three types, and it is often more important than the grade.

Brain tumors are not reported with inked surgical margins in the way that tumors elsewhere in the body are. Instead, the neurosurgeon describes what was achieved during the operation, and an MRI performed within a day or two afterward confirms it. The terms used are gross total resection, meaning no visible tumor remains, and subtotal or partial resection, meaning some remains.

When tumor remains after the first operation, a second operation is often planned, sometimes after chemotherapy has shrunk the tumor and reduced its blood supply. This is called second-look surgery, and in choroid plexus carcinoma it is a deliberate part of the plan rather than a sign that the first operation failed.

What is the prognosis?

The outlook depends on the tumor type and how completely it was removed.

Choroid plexus papilloma. Excellent. More than 9 in 10 children are alive five years after diagnosis, and complete removal is usually curative with no further treatment.
Atypical choroid plexus papilloma. Also favorable, though the tumor returns more often than a papilloma does. Most children do well, and follow-up imaging continues for longer.
Choroid plexus carcinoma. More variable, with survival at five years reported in the range of roughly half to two thirds of children. Complete removal at surgery substantially improves the figure.

Within choroid plexus carcinoma, TP53 status sharply divides outcomes. In published series, children whose carcinoma has a normal TP53 gene have done well, with around 8 in 10 alive at five years. Many were cured without radiation. Children whose carcinoma carries a TP53 change have done considerably worse. These figures come from small numbers of children treated over many years, and more recent reports suggest that complete surgical removal improves outcomes even in the TP53 group.

No figure from a published series can predict what will happen to one child. The neuro-oncology team can give numbers that match your child’s type, grade, TP53 result, and how much tumor was removed.

What happens after the diagnosis?

A team plans care, including a neurosurgeon, a pediatric neuro-oncologist, a radiation oncologist, a neuropathologist, and often a geneticist. Because these tumors are rare, slides are frequently sent for review by a pathologist who specializes in children’s brain tumors.

Doctors usually address hydrocephalus first, or at the same time as the tumor. This may mean a temporary drain or a shunt, a thin tube that carries excess fluid away from the brain. In many children, the fluid build-up settles once the tumor is removed.

For a papilloma that has been completely removed, treatment often ends there, with imaging follow-up to confirm it has not returned. For an atypical papilloma, follow-up is closer and further treatment is considered if the tumor regrows. For a carcinoma, chemotherapy follows surgery, second-look surgery is considered where tumor remains, and radiation is used selectively, taking account of the child’s age and the TP53 result.

Long-term follow-up covers the effects of the tumor and its treatment on development, hearing, vision, hormones, and learning. For children found to have Li-Fraumeni syndrome, follow-up continues into adult life.

Questions to ask your doctor

Which of the three types is described on my child’s report, and what grade was assigned?
If the report says atypical papilloma, how many mitotic figures were counted?
Was the whole tumor removed, and was an MRI done afterward to confirm?
If tumor remains, is a second operation planned, and when?
Was the INI1 stain performed to rule out a rhabdoid tumor?
Was methylation profiling done, and did it confirm the diagnosis?
Should my child have genetic testing for a TP53 change, and when will the result be ready?
If a TP53 change is found, how will that change the treatment plan?
Would radiation be used in my child’s case, and what are the alternatives?
Do my other children, or I, need testing?
Will my child need a shunt, and is that permanent?
Is treatment being given on a clinical trial or a standard protocol?
What follow-up imaging is planned, and for how long?