Medulloepithelioma is a rare, fast-growing embryonal tumor that develops from the early, undifferentiated cells of a developing fetus or infant. These tumors are highly malignant and primarily affect young children. Their complexity stems from their primitive nature and their tendency to arise in sensitive locations. This article provides an overview of its different forms, diagnosis, and treatment strategies.
Types and Locations
The term “embryonal” signifies that the tumor originates from tissues resembling the embryonic neural tube, the structure that develops into the brain and spinal cord. This origin is why the tumor appears almost exclusively in infants and young children, with a peak incidence between six months and five years of age. The primitive cells within these tumors have not matured, which contributes to their rapid growth.
Medulloepithelioma is found in two primary locations. The most common site is intraocular (within the eye), where it is often called a ciliary body medulloepithelioma or, historically, a diktyoma. This form arises from the non-pigmented ciliary epithelium, a layer of cells in the eye that produces intraocular fluid. The average age of diagnosis for this type is between four and five years old.
A rarer and more aggressive form of the tumor occurs in the central nervous system (CNS), which includes the brain and spinal cord. CNS medulloepitheliomas can develop in various parts of the brain, such as the cerebral hemispheres, cerebellum, and brainstem. A third, even more seldom-seen category is peripheral medulloepithelioma, which develops outside the CNS in locations like the sacrum.
Signs and Diagnostic Process
The initial signs of medulloepithelioma depend on its location. For the intraocular type, symptoms are related to changes in the eye’s appearance and function. A common sign is leukocoria, where the pupil has a white reflection instead of the typical red-eye effect in photos. Other symptoms can include:
- Deteriorating vision
- Eye pain
- A visible mass on the iris
- The development of secondary glaucoma or cataracts
When the tumor is in the central nervous system, symptoms are caused by increased pressure within the skull. This can lead to several neurological signs, including:
- Persistent headaches
- Recurrent nausea and vomiting
- Difficulties with balance and coordination (ataxia)
- Seizures
These signs often prompt a more detailed medical investigation.
The diagnostic process begins with a physical examination, such as an ophthalmological exam for suspected intraocular cases or a neurological exam for CNS symptoms. Following this, medical imaging is used to visualize the tumor’s size, shape, and location. Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) scans create detailed pictures of the brain or eye, while an ultrasound B-scan is particularly useful for examining structures within the eye.
While imaging provides strong evidence, a definitive diagnosis requires a biopsy. In this procedure, a small sample of tumor tissue is surgically removed and examined under a microscope by a pathologist. This histopathological analysis reveals the tumor’s cellular structure, confirming it as medulloepithelioma by identifying characteristic features that mimic a primitive neural tube.
Therapeutic Approaches
The treatment for medulloepithelioma is complex and requires a multidisciplinary team of specialists, including pediatric oncologists, surgeons, and radiation oncologists. The primary goal of treatment is the complete removal of the tumor through surgery. The specific surgical approach is dictated by the tumor’s location and extent.
For intraocular medulloepithelioma, the standard treatment is often enucleation, the complete surgical removal of the affected eye. This procedure is frequently recommended because the tumor can be aggressive locally, and it offers the best chance of preventing its spread. This approach provides a high likelihood of a cure for tumors confined to the eye.
In cases of CNS medulloepithelioma, the surgical goal is maximal safe resection, meaning the surgeon removes as much of the tumor as possible without damaging healthy brain tissue. Given the invasive nature of these tumors, achieving a complete removal can be challenging. Surgery is almost always followed by additional, or adjuvant, therapies to address any remaining cancer cells.
Radiation therapy is a common adjuvant treatment for CNS tumors, using high-energy beams to destroy cancer cells where the tumor was located. Chemotherapy uses drugs to kill cancer cells throughout the body and may also be administered.
For aggressive or metastatic tumors, treatment might involve high-dose chemotherapy followed by a stem cell rescue, a procedure that helps the body recover from the intense treatment. The combination of therapies is tailored to each child, balancing effectiveness with potential long-term side effects.
Prognosis and Genetic Factors
The long-term outlook for a child with medulloepithelioma is highly variable. A significant factor is the tumor’s location. Intraocular medulloepitheliomas confined to the eye generally have a more favorable prognosis, as complete surgical removal through enucleation is often possible. In contrast, CNS medulloepitheliomas are associated with a poorer prognosis due to their aggressive nature and the difficulty of complete surgical removal.
The success of the initial surgery is another determinant of the outcome. A complete resection, where no visible tumor is left behind, is associated with better survival rates than a partial resection. The presence of metastasis—the spread of the tumor to other parts of the body like the meninges—also significantly impacts the prognosis.
In some cases, medulloepithelioma is associated with an underlying genetic predisposition known as DICER1 syndrome. This inherited condition increases the risk for a range of rare tumors. Identifying DICER1 syndrome through genetic testing can have implications for the patient’s ongoing monitoring and treatment, and for family members who may also require screening.