Optic nerve glioma pathophysiology
|
Optic nerve glioma Microchapters |
|
Diagnosis |
|---|
|
Treatment |
|
Case Studies |
|
Optic nerve glioma pathophysiology On the Web |
|
American Roentgen Ray Society Images of Optic nerve glioma pathophysiology |
|
Risk calculators and risk factors for Optic nerve glioma pathophysiology |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Simrat Sarai, M.D. [2]
Overview
Pathophysiology
Gross pathology of resected tumors reveals a smooth, fusiform intradural lesion. Macroscopically, these tumors may be solid, gelatinous or cystic. Although having certain gross similarities with oligodendrocytes, closer microscopic, ultrastructural and immunostaining techniques have confirmed their low grade spindle shaped pilocytic (hair like) astrocytes & glial filaments, with the presence of numerous Rosenthal’s fibers. Other histologic findings include arachnoid hyperplasia & mucus-substance. The tumor may start in the anterior end of the optic nerve and proceed backwards intracranially or may arise originally from the optic nerve-chiasmal junction. Occasionally, a glioma from the optic tract or the anterior third ventricle region may involve the chiasma and the optic nerve secondarily. About 40% of optic pathway astrocytomas are fibrillary and 60% are pilocytic. Hypothalamic tumors which have invaded the optic chiasm behave differently, showing evidence of local invasion and histologically are not pilocytic in nature but are similar to other cerebral hemisphere gliomas. OPGs are generally classified as low-grade astrocytomas, although they have a range of growth rates [1]. For this reason, it had been suggested that some OPGs may be hamartomas [11]. Tumors are composed of:
Immature astrocytes, the nuclei of which are regular without mitoses Rosenthal fibers are common Microcystic degeneration seen Focal calcification sometimes present
Several histological patterns of these tumors have been described:
Astrocytic and oligodendroglial proliferation Reticular pattern, involves microcystic foci with mucous-like fluid Leptomeningeal invasion, involves fibrillated cells in bundles
Occasionally pathology is positive for grade II fibrillary astrocytoma.
These tumors are slow growing and are not generally associated with metastatic deposits.
High grade lesions are very rare in children.
The suggested precursor cell is the 02A cell, a glial precursor present in the optic pathway. This precursor can differentiate into both astrocytes and oligodendrolia, which could account for the presence of these cells within the tumor.
Because of the location of these tumors, biopsies are not always performed.
Tumors tend to be more aggressive in adult patients. Tumor de-differentiation is rarely seen in younger children with optic pathway tumors, but may be observed in older children and adults. The tumor may become an anaplastic astocytoma or glioblastoma multiforme.
However, most evidence supports their designation as true, slow-growing neoplasms:
●OPGs are virtually identical histologically to pilocytic astrocytomas seen elsewhere in the nervous system [12]. Sporadic pilocytic astrocytomas often have a tandem duplication of chromosome 7q34 and associated BRAF-KIAA fusion gene, which may eventually provide opportunities for targeted therapy [13,14]. (See "Diagnosis and classification of low-grade gliomas", section on 'Pilocytic astrocytomas'.) ●Their clinical behavior may be aggressive; this is never observed with hamartomas. ●Allelic chromosomal loss occurs in some pilocytic astrocytomas, suggesting that they are clonal lesions arising from inactivation of a tumor suppressor gene. As an example, loss of chromosome 17q (the location of the NF1 gene) is demonstrable in some cases, even in patients without NFI or NF2, suggesting some link between this gene and tumor development [15]. ●OPGs in patients with NF1 exhibit a characteristic loss of neurofibromin (which functions as a negative growth regulator for astrocytes) and increased RAS activation [16,17].
Tumors are composed of:
Immature astrocytes, the nuclei of which are regular without mitoses Rosenthal fibers are common Microcystic degeneration seen Focal calcification sometimes present
Several histological patterns of these tumors have been described:
Astrocytic and oligodendroglial proliferation Reticular pattern, involves microcystic foci with mucous-like fluid Leptomeningeal invasion, involves fibrillated cells in bundles
Occasionally pathology is positive for grade II fibrillary astrocytoma.
These tumors are slow growing and are not generally associated with metastatic deposits.
High grade lesions are very rare in children.
The suggested precursor cell is the 02A cell, a glial precursor present in the optic pathway. This precursor can differentiate into both astrocytes and oligodendrolia, which could account for the presence of these cells within the tumor.
Because of the location of these tumors, biopsies are not always performed.
Tumors tend to be more aggressive in adult patients. Tumor de-differentiation is rarely seen in younger children with optic pathway tumors, but may be observed in older children and adults. The tumor may become an anaplastic astocytoma or glioblastoma multiforme.
Histologically, OPGs are generally low-grade astrocytic tumors that can be placed within the World Health Organization Grade I and can be further categorized as either pilocytic and or fibrillary in nature. The majority of cases are pilocytic. Typical pilocytic histology consists of compact and biphasic architecture with densely cellular areas alternating with loose cystic regions with characteristic Rosenthal fibers and eosinophilic granular bodies. Mitotic figures usually cannot be identified in most samples, and microcalcifications can be seen in 50% of these tumors. Recently, however, a new subgroup of OPGs has been defined which has yet to be categorized within the WHO system: pilomyxoid astrocytomas. Pilomyxoid astrocytomas classically show a markedly myxoid matrix with small compact piloid and highly monomorphous cells. Tumor cells are often arranged radially around vessels in a pattern that mimics the perivascular pseudorosettes seen in other pathological samples such as ependymoma. Tumor samples appear solid without the presence of Rosenthal fibers and eosinophilic granular bodies. Satellitosis of the tumor cells in the surrounding neuropil can be seen, as can the presence of mitotic figures, giving these tumors a more aggressive histology. These tumors were once classified along with their pilocytic counterparts, but, as more cases were identified and a more aggressive natural history was observed, these are now recognized as a separate entity. Kotomar et al. reported a series of patients and noted that there was a marked difference in natural history in patients with pilomyxoid histology, where 14% of patients with this variant had cerebrospinal fluid dissemination of their disease, which was not recognized in patients with the pilocytic variant. The pattern of growth can be either perineural or intraneural in nature. Those patients with NF1 tend to have a perineural growth pattern, whereas those patients who have sporadic OPG tend to have an intraneural growth pattern.