Pilocytic astrocytoma in patient with NF1

Case contributed by RMH Neuropathology

Presentation

Nausea and vomiting. Known NF1.

Patient Data

Age: 18 years
Gender: Female
MRI

MRI brain

Irregularly-shaped cystic mass within the left cerebellar hemisphere measuring 4.1 x 3.6 x 3.3 cm (trans x ap x cc) demonstrating homogeneous T1 signal, high T2 signal and sharply delimited rim enhancement with a vividly enhancing superior nodule (15mm x 8mm). The mass exerts positive mass effect upon the fourth ventricle, displaced to the right, with evidence of ambient cistern effacement mild symmetrical temporal horn dilatation in keeping with mild hydrocephalus. The mass is separate from the left tentorium cerebelli. 

There is associated mild diffusion restriction with ADC depression (not shown) in the periphery of the lesion. No additional intracranial lesion is seen. Minimal surrounding edematous change.

Screening T2 sagittal images of the whole spine were obtained, with no evidence of mass lesion and normal cord signal. Capacious spinal canal. (not shown).

MRI

MRI post op

Left suboccipital craniectomy-related skull defects demonstrated. Expected postsurgical change is noted within the left cerebellar surgical bed with locules of post-operative pneumocephalus and foci of circumferential blood product deposition. Postsurgical leptomeningeal enhancement is demonstrated along the left cerebellar folia and along the left tentorium cerebelli.  No definite residual enhancing tumour mass noted in the left cerebellar hemisphere. There is a shallow ( 3 mm ) subdural haematoma along the dorsolateral aspect of the left cerebellar hemisphere as well as shallow left cerebellar subarachnoid haemorrhage. No interval remote intra-or extra-axial mass lesions. No acute infarcts.

Conclusion:

Expected left cerebellar post-surgical change with no definite large volume tumour residual.

Pathology

Histology

MICROSCOPIC DESCRIPTION:

Paraffin sections show a glial tumour of varying tumour cell density. Tumour cells are a mixture of piloid cells arranged in loose fasciculi and small protoplasmic and fibrillary astrocytes arranged in diffuse sheets. Scattered Rosenthal fibres and granular eosinophilic bodies are noted and areas with a myxomatous/mucinous stroma are also seen. There is prominent microvascular proliferation with endothelial cell hyperplasia. Scattered foci of bland infarct-like necrosis are also seen. No mitotic figures are identified.

IMMUNOHISTOCHEMISTRY:

  • GFAP: positive
  • IDH-1: negative
  • nestin: positive
  • p53: negative
  • MGMT: negative

Epithelial membrane antigen (EMA)   negative 

Topoisomerase labelling index       approximately 5% 

The overall features are of pilocytic astrocytoma (WHO Grade I)

FINAL DIAGNOSIS: Pilocytic astrocytoma (WHO Grade I)

MRI

MRI brain - 6 months later

There has been marked disease progression since the previous scan (which demonstrated minor enhancement in the surgical bed) with a large (2.8 x 4.4 x 3.1 cm) peripherally enhancing mass with multiple regions of nodular enhancement having developed at the site of previous resection, now almost the same size as the lesion was prior to the initial surgery. There has been commensurate increase in T2 signal hyperintensity and mass-effect, although the 4th ventricle remains open and there is no evidence of hydrocephalus. Cerebral blood volume (CBV) is elevated in parts of the enhancing tumour and MR spectroscopy demonstrate elevation of choline and a small lactate peak with a mostly preserved NAA peak. The supratentorial brain is unremarkable.

Conclusion

Significant disease recurrence.

Pathology

Histology - re-resection

MICROSCOPIC DESCRIPTION:

The sections show a variably hypercellular glial tumour within cerebellar white matter. This shows a biphasic architecture. One component consists of cells with pilocytic features. These have elongated hyperchromatic nuclei and bipolar processes which vary in thickness and are arranged in loose fasciculi. Rosenthal fibres are noted within this component. The second component consisist of cells with moderately pleomorphic round and oval vesicular nuclei. These are arranged in diffuse sheets. No mitotic figures are identified. Foci of vascular endothelial cell hyperplasia are identified. There is no necrosis. Tumour is sharply demarcated from adjacent cerebellar cortex but merges gradually with cerebellar swhite matter.

Immunohistochemistry shows strong staining in tumour cells for GFAP and nestin. A small number of tumour cells show nuclear staining for p16. Nuclear staining for MGMT is seen in <15% of tumour cells indicating probable methylation. No staining for IDH-1 or BRAF-V600E is seen. The features are of pilocytic astrocytoma and, except for the absence of necrosis, are similar to those seen in the previous biopsies. The toposiomerase labelling index shows regional variation - approximately 4-6%.

FINAL DIAGNOSIS: NF-1 associated pilocytic astrocytoma (WHO Grade I)

Case Discussion

This case demonstrates aggressive behavior of a pilocytic astrocytoma in a young woman with known NF1. Although pilocytic astrocytomas are generally considered low grade tumours (WHO grade I) they can behave more aggressively, as is the case here. 

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Case information

rID: 25819
Case created: 10th Nov 2013
Last edited: 9th Feb 2017
Inclusion in quiz mode: Included

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