Pilocytic Astrocytoma

Pilocytic astrocytoma is the most common brain tumor in children. It is benign, meaning it grows slowly and does not spread to other organs. Its name comes from the fact that it contains long, thin (hair-like appearing) cells under a microscope. It most commonly occurs in the cerebellum, followed by the optic pathways and brainstem region. When completely removed surgically, recovery is achieved in the vast majority of patients and it is one of the brain tumors with the best prognosis.

Symptoms vary depending on tumor location. In cerebellar tumors, unsteady gait and frequent falls, headache, morning nausea and vomiting, eye tremor, and hand-arm incoordination are seen. If optic pathways are affected, vision loss, strabismus, and protrusion of the eye may occur. If the central structure below the visual cortex is affected, growth retardation, weight changes, delayed puberty, and excessive drinking and urination may be seen. In brainstem tumors, double vision, difficulty swallowing, and speech disorders may occur. In babies, rapid head growth, bulging fontanelle, excessive sleepiness, and vomiting are important warning signs.

The main diagnostic methods include: (1) Contrast-enhanced brain MRI - typical appearance is a small contrast-enhancing solid component within a fluid-filled cyst; (2) Spinal MRI - to determine if the tumor has extended to the spinal cord (this is rare); (3) Ophthalmologic examination - visual acuity, visual field, and fundoscopic examination if optic pathways are affected; (4) Evaluation for Neurofibromatosis Type 1 - especially in optic pathway tumors; (5) Microscopic examination of tissue obtained during surgery (definitive diagnosis); (6) Investigation of certain genetic alterations for targeted drug therapy.

Surgery is the foundation of treatment. If the tumor can be completely removed, long-term remission is achieved in the vast majority of patients without need for additional treatment. Complete removal is generally possible in cerebellar tumors. However, in critical regions such as the optic pathways, central structures below the visual cortex, and brainstem, complete removal may cause vision loss or hormonal problems; in this case, drug therapy together with biopsy is preferred. If part of the tumor remains, the risk of recurrence increases; in case of recurrence, reoperation is considered first.

Most pilocytic astrocytoma cells contain certain genetic alterations in a signaling pathway that regulates cell growth. These alterations are important in terms of using drugs that directly target that pathway. In suitable cases, especially when surgery cannot be performed or the tumor continues to grow, oral targeted drugs that are generally well-tolerated may be considered. The decision of which patient is suitable is made through genetic examination of the tumor and evaluation by the specialist team.

Drug (chemotherapy) treatment is used in the following situations: (1) In tumors that cannot be surgically removed (optic pathways, central structures below visual cortex, brainstem); (2) When the tumor continues to grow after partial removal; (3) In young children to avoid radiation therapy. Treatment usually lasts several months and is particularly effective in young children and optic pathway tumors. Optic pathway tumors occurring with Neurofibromatosis Type 1 usually follow a stable course; in this case, monitoring alone may be sufficient, and drug therapy is considered if growth is seen.

Radiation (radiotherapy) treatment is used in limited cases; considered more often in older children and when drug therapy is insufficient. In young children, it is avoided as much as possible due to possible effects on learning and development. In the short term, fatigue, headache, and hair loss may be seen. In the long term (months to years later), learning difficulties, hormone deficiencies, and developmental problems may occur. Therefore, in young children, drug therapy or targeted drugs are preferred first; radiation therapy is the last option.

The likelihood of recurrence depends on how much of the tumor could be removed. When completely removed, this probability is low; it is higher when part of the tumor remains. Recurrence usually occurs at or near the surgical site. In case of recurrence, reoperation is considered first; then targeted drugs, chemotherapy, or (if not given previously) radiation therapy may follow. Most recurrent cases are controlled with retreatment and long-term prognosis is generally good.

Neurofibromatosis Type 1 is an inherited (genetic) disease. In some children with this disease, pilocytic astrocytoma may develop in the optic pathways; this is usually noticed at an early age. These tumors are usually asymptomatic or follow a stable course; growth is seen in only some. In asymptomatic cases, monitoring is performed with MRI and ophthalmologic examination at regular intervals; if there is growth or vision loss, drug therapy is considered, and surgery remains limited due to the risk of vision loss. In diagnosing Neurofibromatosis Type 1, findings such as café-au-lait spots on the skin, freckling in the armpits/groin, and family history are evaluated.

Follow-up is planned according to tumor status. After complete removal, MRI is performed several times in the first year, then yearly; if no recurrence is seen for several years, monitoring can be spaced out. If part of the tumor remains or drug therapy is being given, follow-ups are more frequent. If optic pathways are affected, regular ophthalmologic examination is performed; if the hormone center region is involved, hormone monitoring is done. Long-term prognosis is generally very good; after complete removal, the vast majority of children live healthy lives. When part of the tumor remains, the risk of recurrence is higher, but it is usually controlled with retreatment.