Uncommon low-grade brain tumors

Abstract

The 2016 World Health Organization (WHO) classification of primary central nervous system (CNS) tumors includes numerous uncommon (representing ≤1% of tumors) low-grade (grades I-II) brain neoplasms with varying clinical behaviors and outcomes. Generally, gross tumor or maximal safe resection is the primary treatment. Adjuvant treatments, though their exact role is unknown, may be considered individually based on pathological subtypes and a proper assessment of risks and benefits. Targetable mutations such as BRAF (proto-oncogene B-Raf), TRAIL (tumor necrosis factor apoptosis inducing ligand), and PDGFR (platelet derived growth factor receptor) have promising roles in future management.

Keywords: brain tumors; low-grade; mutations; treatment.

Fig. 1

Histopathology of uncommon low-grade brain tumors (all hematoxylin and eosin stains. Scale bars 100 μm unless otherwise stated). (A) Ganglion cell tumor: nests of abnormal ganglion cells are a feature of ganglion cell tumors, which may also have a neoplastic glial element. Less specific features include eosinophilic granular bodies and perivascular lymphocytes. (B) Dysembryoplastic neuroepithelial tumors are characterized by large pyramidal neurons “floating” in pools of mucin. This feature is unusual in oligodendroglioma, the main histological differential diagnosis. (C) Desmoplastic infantile astrocytomas/gangliogliomas have an attachment to the overlying dura as seen in this low power image as the thick fibrous tissue at the top of the image. (D) Desmoplastic infantile gangliogliomas combine a compact spindle cell element, with astrocytic features, with occasional small ganglioid cells with features intermediate between astrocytes and ganglion cells (arrow). (E) Angiocentric gliomas are characterized by an infiltrative growth pattern of slender, monomorphic, bipolar cells that form angiocentric rosettes and accumulate under the pial surface. (F) Pleomorphic xanthoastrocytomas combine spindle shaped astrocytes and large, multinucleated, pleomorphic cells (arrows). Lipid vacuoles, eosinophilic granular bodies, and perivascular lymphocytes are also common features. (G) Rosette-forming glioneuronal tumors are characterized by bland neurocytes forming rosettes with core of neuropil-like material that is immunoreactive for synaptophysin (not shown). (H) Chordoid glioma: cords of epithelioid cells embedded in a myxoid background lend a chordoma-like quality to this neoplasm. Nuclei are bland and mitotic figures infrequent. (I) Astroblastoma: extensive sclerosis of blood vessels is common in this neoplasm. Tumor cells are oriented around the central vessel, defining the astroblastic rosette. (J) Choroid plexus papilloma: a papillary architecture composed of epithelium overlying fibrovascular cores. Mitotic figures are rare in this grade I example. Atypical examples display raised mitotic activity and variable loss of the papillary pattern. (K) Dysplastic gangliocytoma of the cerebellum is best appreciated at low magnification where the thickening of the affected cerebellar cortex and loss of the darkly staining granular layer are most apparent. Compare with the normal cortex in the top right of the image. (L) Neurocytoma: neurocytic cells with uniformly round nuclei are typical features. Occasional poorly formed rosettes may feature as in this example. Immunoreactivity for synaptophysin would be expected. (M) Subependymal giant cell astrocytoma. Large cells with features intermediate between ganglion cells and astrocytes characterize this lesion, which is strongly associated with tuberous sclerosis complex.

Fig. 2

Dysembryoblastic neuroepithelial tumor (A–E) on CT (A), on T2W (B), and on FLAIR MRI (C) shows a multicystic lesion in the left medial temporal lobe. It is predominantly hypodense, T2 hyperintense, and with suppression on FLAIR. No surrounding edema. Magnetic resonance (MR) fast spoiled gradient echo (D) and post-contrast T1W (E) images on coronal plane demonstrate the hippocampal involvement with no contrast enhancement. Desmoplastic infantile ganglioglioma (F–I) on T2W MR (F) and FLAIR (G) shows a lesion centered on the right frontal lobe that contains cystic (confirmed with FLAIR suppression) and solid areas (isointense to gray matter). There is mass effect with shift of the midline structures and compression of the right lateral ventricle. Post-contrast T1W MRIs (H–I) show avid enhancement of the solid components at the lateral aspect as well as a broad dural tail/attachment.

Fig. 3

Pleomorphic xanthoastrocytoma. (A–D) Pre- and post-contrast CT (A, B) images show an isodense, partially solid, and cystic lesion within the right occipital lobe with small amount of calcification. There is avid contrast enhancement of the solid component with the cystic component showing a rim of peripheral enhancement. The adjacent lateral ventricular atrium is compressed. T2W and post-contrast T1W MRIs (C, D) illustrate the cystic (hyperintense on T2W) and solid (isointense to gray matter on T2W) components of the well-circumscribed lesion which abuts the leptomeninges medially. The areas of low T2W signal represent calcification and blood degradation products. There is adjacent vasogenic edema in the occipital and parietal white matter. Rosette-forming glioneural tumor (E–H): T1W (E) and post-contrast T1W MRI (F) show an isointense lesion filling and expanding the aqueduct and fourth ventricle, which has a heterogeneous ring like enhancement with gadolinium. There is a well-defined border without invasion into surrounding structures. FLAIR images (G–H) illustrate a midline lesion in the fourth ventricle at the level of the middle cerebellar peduncle. There are enhancing nodules more superiorly lining the ependymal surfaces of the lateral ventricles.

Fig. 4

Astroblastoma (A–D). CT (A) and T2W MRI (B) show a lesion centered on the right inferior frontal gyrus, involving the right insular and subinsular cortex, the right temporal stem, and the right medial temporal gyrus. The lesion contains solid components with areas of cystic degeneration and small foci of calcification and there is adjacent edema resulting in mild compression of the right lateral ventricle. Contrast-enhanced T1W MRI (C, D) shows a predominantly hypointense lesion with minimal heterogeneous contrast enhancement. Dysplastic cerebellar gangliocytoma (E–H): T2W MRI (E, F) shows a lesion within the left superior cerebellar cortex with apparent widening of the cerebellar folia seen as hyper- and isointense striations relative to gray matter. There is no evidence of compression of the fourth ventricle. T1W MRI (G, H) demonstrates a slightly smaller left cerebellar hemisphere, which is more easily appreciated on coronal images.