To date, approximately 100 cases of chordoid glioma have been reported in the literatures. They most occur frequently in adults. Chordoid gliomas occupy the anterior portion of the third ventricle, with larger tumors also filling the middle and posterior aspects. They generally arise in the midline and displace normal structures in all directions as they enlarge (2). While there were a few reports that chordoid glioma located outside the third ventricle, such as hemisphere, thalamus, parieto-temporal extra-ventricular, juxtaventricula et al (8). This made the diagnosis difficult and had challenges. Considering these entities may be not limited to the third ventricle, the nomenclature may require an amendment with more clinical and radiological evidence supports.
Most chordoid glioma patients had signs and symptoms of obstructive hydrocephalus, including headache, nausea, vomiting and ataxia. Other clinical features include endocrine abnormalities reflecting hypothalamic compression, visual field disturbances due to compression/displacement of the optic chiasm, and personality changes including psychiatric symptoms and memory abnormalities.
In imaging, chordoid gliomas present as solid or cystic-solid and characteristically exhibit a well-circumscribed border within the third ventricle. On MRI, the solid portion of tumors showed isointense or hypointensity on T1-weighted and hyperintensity in most cases on T2WI. (8).
In microscopy, chordoid gliomas are most often composed of clusters and couds of epithelioid tumor cells within a variably mucinous stroma that typically contains a lymphoplasmacytic infiltrate. Neoplastic nuclei are moderate in size, ovoid, and relatively uniform. Mitoses are absent in most tumors, when present, they are rare. A stroma lymphoplasmacytic infiltrate, often containing numerous Russell bodies, is a consistent finding. In the updated 4th edition of the WHO Classification of Tumours of the CNS (2016) (4) described that maybe there were three less common histological patterns had been reported: a solid pattern with sheets of polygonal epithelioid tumor cells without mucinous stroma, a fusiform pattern with groups of spindle-sheped cells among loose collagen, and a fibrosing pattern with abundant fibrosis. The fibrosing pattern tends to be more common in older patients. Other (rare) tissue patterns include pappilary [3], alveolar, and pseudoglandular patterns. Individual tumor cells have abundant esoinophilic cytoplasm. In some cases, limited glial differentiation in the form of coarsely fibrillar processes can also be seen. Reactive astrocytes, Rosenthal fibres, and often chronic inflammatory cells including lymphocytes, plasma cells, and Russell bodies are seen in adjacent non-neoplastic tissue. In our case, there were common pattern and three less common patterns and three rare patterns. Such case was really rare.
The immunohistochemical feature of chodoid glioma is the tumor cells strong reactivity for GFAP, vimentin and TTF-1. CD34 is positive focally. Immunoreactivity for S100, EMA and cytoderatin is variable. Neuronal and neurosendocrine markers, such as synaptophysin, neurofilaments, and chromograin-A, are consistently negative. The proliferation is low. Neither IDH mutation nor BRAF V600E mutation were found in the literature. In our case, there were focal tumor cells positive for NeuN which had no related literature reports retrieved.
Goode et al reported that all the 13 chordoid gliomas had a recurrent D463H missense mutation in PRKCA, which localizes in the kinase domain of the encoded PKCα (2). Our case had D463H missense mutation and had no D294G mutation in PKCα.
Differential diagnosis of histopathology
- Adenocarcinoma brain metastases: The patient has a history of adenocarcinoma of other organs. Immunohistochemical, the CKp was strong positive.
- Pituitary ependymoma: At present, only 10 pituitary ependymoma cases with TTF-1 positive have been reported in the English literature. All these cases located in the pituitary (7).
- Ependymoma of the third ventricle: The ependymoma of the third ventricle was positive for TTF-1 in the literature reported. While it’s histology was typical morphology of the ependymoma (9).
- Meningiomas: Meningiomas maybe have adenoid structures. However, in immunohistochemical, EMA is diffusely positive and TTF-1 is negative.
- Pituitary adenoma: The histology of the tumor is adenoid structures, but the tumor is located in the pituitary gland. Immunohistochemical, the tumor cells are strongly diffuse positive for Syn and negative for TTF-1.
- Solitary fibrous tumor/haemangiopericytoma: Histologically, they are maybe have adenoid structures in some area. Immunohistochemically, the tumor cells are positive for STAT-6 and negative for TTF-1.
The ultrsatructural demonstration of microvilli and hemidesmosome-like structures in chordoid glioma support an ependymal histogensis. Further evidence of ependymal or specialized ependymal differentiation has been supplied by a report of abnormal cilia in a juxtanuclear location (6). The presence of a cytological zonation pattern and secretory vesicles indicated a specialized ependymal differentiation, as might be expected of cells derived from a circumventricular organ such as the lamina terminalis. A recent study reported strong expression of TTF-1 in both chordoid gliomas and the organum vasculosum of the lamina terminalism, suggesting an organum vasculosum origin (1).
Chordoid gliomas are histologicaly low-grad. Gross total resection is the treatment of choice and can result in long-term recurrence-free survival. However, the tumors location in the third ventricle and their attachment to hypothalamic and suprasellar structures often make complete resection impossible. Postoperative tumor enlargement has been noted in half of all patients who undergo subtotal resection. Among the reported cases of chordoid gliomas, approximately 20% of the patients died in the perioperative period or from tumor regrowth (3).