Pilocytic astrocytoma
Updates to Case Attributes
This cases illustrates a large cystic mass lesion arising from the left inferior cerebellar hemisphere with an enhancing solid component and associated obstructive hydrocephalous. In the patient's age group and with these image features, haemangioblastoma and pilocytic astrocytoma must be considered.
Haemangioblastoma typically occur in the young adult, and although they are the most common posterior fossa mass in a young adult, they are nonetheless uncommon in absolute terms, accounting for only 1-2.5% of all intracranial tumours. They have a peak incidence around 30-60 years of age.
Pilocytic astrocytomas are tumours of young people, with 75% occurring in the first two decades of life, typically late in the first decade (9-10 years). There is no recognised gender predisposition.
Pilomyxoid astrocytomas (PMA) are a recently described variant of pilocytic astrocytoma with unique clinical and histopathologic characteristics, being considered a WHO grade II tumour. PMA was originally reported as arising in the hypothalamus or optic chiasm of an infant or young child, however it is also know that they may also occur in the posterior fossa and in the spinal cord 1.
This case shows an atypical expected age for PMA, which the mean age at diagnosis is around 18 months 1.
- +<p>This cases illustrates a large cystic mass lesion arising from the left inferior cerebellar hemisphere with an enhancing solid component and associated obstructive hydrocephalous. In the patient's age group and with these image features, haemangioblastoma and pilocytic astrocytoma must be considered.</p><p><a href="/articles/haemangioblastoma-central-nervous-system-1">Haemangioblastoma</a> typically occur in the young adult, and although they are the most common posterior fossa mass in a young adult, they are nonetheless uncommon in absolute terms, accounting for only 1-2.5% of all intracranial tumours. They have a peak incidence around 30-60 years of age. </p><p><a href="/articles/pilocytic-astrocytoma">Pilocytic astrocytomas</a> are tumours of young people, with 75% occurring in the first two decades of life, typically late in the first decade (9-10 years). There is no recognised gender predisposition. </p><p><a title="Pilomyxoid astrocytomas" href="/articles/pilomyxoid-astrocytoma">Pilomyxoid astrocytomas (PMA)</a> are a recently described variant of pilocytic astrocytoma with unique clinical and histopathologic characteristics, being considered a <a href="/articles/cns-tumours-classification-and-grading-who">WHO grade II</a> tumour. PMA was originally reported as arising in the hypothalamus or optic chiasm of an infant or young child, however it is also know that they may also occur in the posterior fossa and in the spinal cord <sup>1</sup>. </p><p>This case shows an atypical expected age for PMA, which the mean age at diagnosis is around 18 months <sup>1</sup>. </p>
References changed:
- 1. Komotar RJ, Mocco J, Jones JE et-al. Pilomyxoid astrocytoma: diagnosis, prognosis, and management. Neurosurg Focus. 2006;18 (6A): E7. <a href="http://www.ncbi.nlm.nih.gov/pubmed/16048293">Pubmed citation</a><span class="auto"></span>
Updates to Study Attributes
There is a large predominantly cystic mass arising from the inferior left cerebellarhemispherecerebellar hemisphere measuring up to 33 mm in the transverse diameter. A solid enhancing component isdemonstratedis demonstrated inferiorly. There is considerable associated mass effect with partialcompressionpartial compression of the inferior fourth ventricle. The lateral and third ventricles aredilatedare dilated. There is deformity of the left cerebellar peduncle and distortion of theadjacentthe adjacent brainstem.
Thee cerebral hemispheres are intact and no additional intracranial mass lesion isseenis seen superior to the tentorium. There is no abnormal leptomeningeal contrastenhancementcontrast enhancement. The basal cisterns are however to some extent effaced.
Bony calvarium is normal and there is no calvarial erosion.
There is no convincing evidence of tonsillar distinct on subsequent sagittalreconstruction.
CONCLUSION:Large cystic mass lesion arising from the left inferior cerebellar hemisphere withenhancing solid component measuring 33 mm. In the patient's age group, likelydiagnosis diagnosis is that of a haemangioblastoma. Additional consideration would bethat of pilocytic astrocytoma although the patient's age is not typical.
Littlesignificant vasogenic oedema to suggest infective aetiology. MRI imaging isrecommended for further characterisation.
These findings have been discussed with the attending physician, Dr Quarin , at 20:30AEDT.
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Centred in the medial aspect of the left cerebellar hemisphere, there is a mixed solid and cystic mass, measuring 3.6 cm x 3.6 cm x 2.9 cm. The solid component is located medially and measures 2.8 cm x 2.7 cm x 2 cm. The solid component enhances vividly and homogeneously. There is a cystic component superiorly within the cerebellum, as well as inferiorly, extending as far as the upper cervical spinal cord. The cystic component is located posterior to the cord here, and there is mild flattening of the cord.
There is peripheral enhancement of the cystic component of the mass. The solid component demonstrates homogeneous T2 hyperintensity. There are noNo flow void is identified.
There is mild surrounding vasogenic oedema. The mass compresses the fourth ventricle, and there is obstructive hydrocephalus with evidence of mild transependymal CSF flow.
No restricted diffusion or susceptibility artefact.
No No supratentorial mass is identified.
Single voxel spectroscopy demonstrates elevated choline and metabolite depletion to the right of the spectrum.
Conclusion:
Posterior fossa mixed cystic and solid mass with associated obstructive hydrocephalous. The favoured diagnosis is pilocytic astrocytoma. Haemangioblastoma is a less likely differential.
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MICROSCOPIC DESCRIPTION: Paraffin sections show a moderately hypercellular glial tumour involving cerebellum. Tumour cells are a mixture of plump piloid cells and cells with round and oval nuclei and delicate processes. Both cell types show moderate nuclear pleomorphism. No mitotic figures are identified. There is no microvascular proliferation and no necrosis is seen. Small numbers of Rosenthal fibres are identified. A moderate amount of extracellular Alcian Blue positive myxomatous material is noted throughout the tumour. Tumour gradually merges with surrounding cerebellar parenchyma. Gliosis and patchy loss of Purkinje cells is noted in the cerebellar cortex.
IMMUNOHISTOCHEMISTRY:
- GFAP positive
- Nestin positive (moderate)
- ATRX positive (not mutated)
- IDH-1 R132H negative (not mutated)
- MGMT positive (likely unmethylated)
- p53 negative
- p16 negative
- Topoisomerase labelling index: Approximately 2%.
- The features are of pilomyxoid astrocytoma (WHO Grade II).
DIAGNOSIS: "Posterior cranial fossa tumour": Pilomyxoid astrocytoma (WHO Grade II)
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