Disclosure
Background: Juvenile pilocytic astrocytomas occur more often in children and young adults. They are the most common astrocytic tumors in children, accounting for 80-85% of cerebellar astrocytomas and 60% of optic gliomas. Juvenile pilocytic astrocytomas usually arise in the cerebellum, brainstem, hypothalamic region, or optic pathways, but they can occur in any area where astrocytes are present, including the cerebral hemispheres and the spinal cord. The most common site of occurrence of juvenile pilocytic astrocytoma is in the cerebellum. These tumors are usually discrete, indolent lesions associated with cyst formation. The cysts can be unilocular or multilocular, with an associated tumor nodule. The most common presenting symptoms are associated with increased intracranial pressure due to mass effect or hydrocephalus. They include headache, nausea, vomiting, irritability, ataxia, and visual complaints, depending on the site of occurrence. Pathophysiology: The etiologic factors of juvenile pilocytic astrocytomas are unknown. Transformation to a malignant high-grade tumor is rare. Juvenile pilocytic astrocytoma is associated with neurofibromatosis type 1 (NF1), an autosomal dominant disorder characterized by the development of benign and some malignant tumors. Optic gliomas, 60% of which are pilocytic astrocytomas, are common tumors in patients with this disorder. Patients with optic pilocytic astrocytomas associated with NF1 usually have better outcomes than those of other patients with juvenile pilocytic astrocytomas because the tumor is more likely to be confined to the optic nerve. Bilateral optic gliomas are more common in patients with NF1. Macroscopically, the tumor is a well-circumscribed mass that commonly has a large cyst and a focal mural nodule. The tumor can also be solid, with or without cystic degeneration. Microscopically, juvenile pilocytic astrocytoma demonstrates well-differentiated pilocytes with hairlike glial processes associated with microcysts that contain mucopolysaccharide material. The pilocytes are mixed with Rosenthal fibers, eosinophilic rod-shaped bodies and granular eosinophilic bodies, which are commonly found in indolent neoplasms. Capillary formation is usually present. Juvenile pilocytic astrocytomas are not graded histopathologically. The 4 morphologic criteria of the Daumas-Duport system—nuclear atypia, mitoses, endothelial proliferation, and necrosis—can sometimes be found in pilocytic astrocytomas, but they have no known prognostic significance. Frequency:
Mortality/Morbidity: Juvenile pilocytic astrocytoma has a better prognosis than most other astrocytomas. If gross total resection is possible, the 10-year survival rate is as high as 90%. After subtotal resection or biopsy, the 10-year survival rate is still as high as 45%. Morbidity is related to the location of the tumor and to the associated complications of tumor resection. Sex: Juvenile pilocytic astrocytomas have an equal sex incidence. Age: The peak incidence is 5-14 years. Age affects the clinical course of optic nerve gliomas. Children younger than 5 years have a mortality rate comparable to that of patients aged 5-20 years. Anatomy: Juvenile pilocytic astrocytomas usually arise in the cerebellum, brainstem, hypothalamic region, or optic pathways, but they can occur in any area where astrocytes are present, including the cerebral hemispheres and spinal cord. Clinical Details: The presenting signs and symptoms depend on the location of the tumor. The most common symptoms are due to increased intracranial pressure as a result of mass effect or hydrocephalus. These include nausea, vomiting, headache, ataxia, and visual complaints. Astrocytic tumors are categorized into pilocytic and ordinary subtypes. The ordinary subtypes include fibrillary, protoplasmic, and gemistocytic tumors. Ordinary astrocytomas have a worse overall prognosis because of their more aggressive behavior and their potential to undergo malignant transformation. The classic juvenile pilocytic astrocytoma arises in a cerebellar hemisphere and is easily seen on CT scans and MRIs as a well-circumscribed lesion with an associated macrocyst. The nodular portion of the lesion usually demonstrates homogenous contrast enhancement. Calcification may be present in 10% of juvenile pilocytic astrocytomas. Other low-grade gliomas are typically hypoattenuating or hypointense, poorly defined, nonenhancing lesions on CT scans and MRIs. Preferred Examination: The preferred examination is MRI. Pilocytic astrocytomas are typically treated with surgery and MRIs are useful in outlining the contrast-enhancing tumor. The tumor should be completely resected whenever possible. Cyst wall enhancement can be seen on MRIs and indicates that the entire cyst should be resected. Limitations of Techniques: Identifying low-grade gliomas by using radiologic findings alone results in an incorrect diagnosis in as many as 50% of the cases.
Brain, Metastases
Supratentorial juvenile pilocytic astrocytoma
Findings: Juvenile pilocytic astrocytomas may occur anywhere in the central nervous system. On CT scans, these astrocytomas cannot be reliably differentiated from other more diffuse or aggressive tumors on the basis of imaging characteristics alone. CT may show hypoattenuating or isoattenuating areas, or both. Enhancement varies from none to extensive, with varying degrees of necrosis and cyst formation. Supratentorial malignant glioma, ependymoma, and oligodendroglioma may have similar appearances. Lower-grade tumors tend to be homogeneous and well circumscribed. Peritumoral edema is mild, and no hemorrhage is present. Higher-grade tumors have more surrounding edema, are more heterogeneous in density, and may have areas of hemorrhage. Optic nerve and optic chiasm hypothalamic juvenile pilocytic astrocytomas A subset of astrocytic tumors occurs in patients with NF1. These may involve the optic nerves, the optic chiasm, and the optic tracts. Most are juvenile pilocytic astrocytomas, but their imaging characteristics are not specific with regard to their histologic features. Varying degrees of cystic change and enhancement are demonstrated. These tumors may appear smooth, fusiform, eccentric, or lobulated. CT demonstrates the intraorbital optic nerves and is sensitive in the detection of the tumors. About 20% of juvenile pilocytic astrocytomas have microscopic calcifications, which are less frequently seen on CT scans than on other images. Posterior fossa juvenile pilocytic astrocytomas Among pediatric tumors of the posterior fossa, astrocytomas are second in frequency only to medulloblastoma. Approximately 75% of cerebellar astrocytomas are of the pilocytic type, but imaging does not help in predicting their histologic features because fibrillary forms can have similar appearances. Imaging characteristics are most typical for cerebellar tumors during the first decade of life. The typical presentation of a juvenile pilocytic astrocytoma is of a large cerebellar hemispheric or vermian mass that is predominantly cystic and that is occurring in a child younger than 10 years. Nonenhanced CT scans show hypoattenuation or isoattenuation. Tumor contrast enhancement is homogeneous or heterogeneous depending on the extent of the cystic necrotic changes. Degree of Confidence: See Findings above. |
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Findings: On T1-weighted images, the signal intensity is generally low, and on T2-weighted images, the signal intensity is increased. Enhancement patterns are similar to those depicted on CT scans. Optic nerve and optic chiasm hypothalamic juvenile pilocytic astrocytomas Optic chiasm hypothalamic gliomas cannot be separated by their site of origin and are considered as a single entity. On T1-weighted images, the signal intensity is low. On T2-weighted images, the signal intensity is generally increased. The T2 signal intensity increase may extend as far as the optic radiations, but it is not correlated directly with the presence of tumor. Enhancement is similar to that on CT scans. Fat-saturated T1-weighted postcontrast MRI of the intraorbital optic nerves is a sensitive method for demonstrating the tumor. Posterior fossa juvenile pilocytic astrocytomas The signal intensity is low with T1-weighted sequences and high with T2-weighted sequences. Enhancement patterns are similar to those on CT scans. MRI is less sensitive to calcium than CT. Vermian tumors are often associated with hydrocephalus. Three general tumor patterns are found:
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape. Degree of Confidence: Specific findings on MRI can be suggestive of juvenile pilocytic astrocytomas, but they are not diagnostic for this disease. Metastatic disease neoplasm and high-grade glioma cannot be excluded on the basis of radiographic findings. For posterior fossa tumors, the commonest differential diagnostic possibilities include medulloblastoma and ependymoma. Metastases are rare in childhood. Medulloblastomas are typically isoattenuating to hyperattenuating on nonenhanced CT scans. Ependymomas may extend laterally or inferiorly to the foramina of Luschka or Magendie, with extension to the cerebellopontine angle or through the foramen magnum respectively. They are isoattenuating to hyperattenuating on nonenhanced CT. About 50% of ependymomas may exhibit small multifocal calcifications on CT scans. The major differential diagnostic consideration for optic chiasm/hypothalamic glioma is craniopharyngioma.
Findings: Angiography is usually not useful in diagnosis except to exclude an aneurysm in the presence of a suprasellar tumor mass.
Intervention: The primary therapy for juvenile pilocytic astrocytomas is complete surgical resection. In cerebellar lesions, gross total resection is possible in more than 70% of cases. With completely resected tumors, no adjuvant therapy is needed. In patients in whom tumor resection is incomplete, the clinical course can often be benign with postoperative stabilization of the disease, despite positive finding of tumor in surgical margins. For this reason, postoperative radiation therapy in these patients is controversial. Frequent follow-up with MRI is helpful. To patients in whom a juvenile pilocytic astrocytoma limited to 1 orbit causes proptosis and significant visual loss, surgical resection is offered. Patients with NF1, with posteriorly located optic pathway tumors, and juvenile pilocytic astrocytomas not appreciably affecting vision are treated symptomatically. Shunts are placed to treat hydrocephalus. Treatment for endocrine dysfunction is administered as indicated. Patients with juvenile pilocytic astrocytomas in the posterior optic pathway and visual deterioration or progressive neurologic deficits but not NF1 are treated surgically.
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
){kind=small}
