Rosette-forming glioneuronal tumours (RGNTs) are rare, usually midline, tumours that involve the fourth ventricle and/or aqueduct of Sylvius.
Although relatively well circumscribed on MRI and clinically indolent, they often invade surrounding tissues, involving the cerebellum, pons and even the pineal region. There are often cystic components and they tend to have heterogeneous contrast enhancement. They are considered WHO grade I lesions in the current (2016) WHO classification of CNS tumours.
Rosette-forming glioneuronal tumours are typically diagnosed in younger adult patients with a mean age of 30 years 1,6.
Symptoms are non-specific and mainly depend on the location of the tumour. Commonly they present with ataxia and headache.
Rosette-forming glioneuronal tumours are originally described in the region of the 4th ventricle (~60%) often with variable local parenchymal extension 3. A recent literature review 3 has demonstrated these tumours outside the characteristic location including the cerebellum hemispheres, cerebellopontine angle, pineal gland, midbrain tectum, thalamus, third ventricle, optic chiasm and spinal cord.
Rosette-forming glioneuronal tumours contain both neurocytic and astrocytic components. The neurocytic component, which is a minor component but allows for diagnosis of this tumour, forms perivascular pseudorosettes or neurocytic rosettes surrounding eosinophilic neuropil cores 6. The larger glial component resembles that of pilocytic astrocytomas, including the presence of Rosenthal fibres 6.
Immunohistochemistry is consistent with the biphasic nature of this tumour with both glial and neurocytic patterns identified.
The glial component demonstrates:
The neurocytic component demonstrates:
- MAP2: positive
- neuron-specific enolase: positive
- synaptophysin: positive in the centre of the neurocytic rosettes
Proliferation index (Ki-67) is usually low, <3% 6.
Rosette-forming glioneuronal tumours have variable solid-cystic components 3:
- entirely solid: 40%
- mixed solid and cystic: 35%
- entirely cystic: 25%
On CT these tumours are of variable appearance reflecting the solid and cystic components. Calcification is seen in approximately a quarter of cases 3.
As expected, the cystic components demonstrate high T2 signal, whereas the solid components demonstrate variable gadolinium enhancement 3.
Treatment and prognosis
If complete resection is achievable, which depends mostly on the location of the tumour, then a cure is possible to surgery alone.
The main differential diagnosis is pilocytic astrocytoma. The other differential diagnoses will, to a degree, depend on the location and include:
- pilocytic astrocytoma
- gangliogliomas and gangliocytomas
- pleomorphic xanthoastrocytoma (almost always hemispheric)
- papillary glioneuronal tumour (usually hemispheric)
- 1. Komori T, Scheithauer BW, Hirose T. A rosette-forming glioneuronal tumor of the fourth ventricle: infratentorial form of dysembryoplastic neuroepithelial tumor? Am. J. Surg. Pathol. 2002;26 (5): 582-91. Am. J. Surg. Pathol. (link) - Pubmed citation
- 2. Edgar MA, Rosenblum MK. Mixed glioneuronal tumors: recently described entities. Arch. Pathol. Lab. Med. 2007;131 (2): 228-33. doi:10.1043/1543-2165(2007)131[228:MGTRDE]2.0.CO;2 - Pubmed citation
- 3. Hsu C, Kwan G, Lau Q et-al. Rosette-forming glioneuronal tumour: imaging features, histopathological correlation and a comprehensive review of literature. Br J Neurosurg. 2012;26 (5): 668-73. doi:10.3109/02688697.2012.655808 - Pubmed citation
- 4. Pimentel J, Resende M, Vaz A et-al. Rosette-forming glioneuronal tumor: pathology case report. Neurosurgery. 2008;62 (5): E1162-3. doi:10.1227/01.neu.0000325879.75376.63 - Pubmed citation
- 5. Arai A, Sasayama T, Tamaki M et-al. Rosette-forming glioneuronal tumor of the fourth ventricle-case report. Neurol. Med. Chir. (Tokyo). 2010;50 (3): 224-8. Pubmed citation
- 6. Louis DN, Ohgaki H, Wiestler OD, Cavenee WK "WHO Classification of Tumours of the Central Nervous System. 4th Edition Revised" ISBN: 9789283244929