Freiburg Neuropathology Case Conference

A 39-year-old man reported that he had experienced several short episodes of speech arrest and neologistic jargon aphasia in the last 6 months. He further described a noticeable limitation of his memory function. Convulsive seizures or loss of consciousness had not occurred. The patient presented without focal neurological deficits, speech disorders or apparent cognitive impairment. Cranial magnetic resonance imaging (MRI) revealed a left temporal lesion. Further epilepsy diagnostics were not performed in view of the clear causal relationship with the lesion.

The multidisciplinary tumor committee recommended total resection of the left temporal lesion because a high-grade glioma was suspected. A temporal craniotomy was performed. The left temporopolar cortex overlying the tumor was removed. It was a well-demarcated and relatively solid tumor, and these features allowed uncomplicated circular resection along the anatomical tumor borders. Most importantly, dissection against the basal ganglia, usually the most challenging step in the resection of temporal gliomas due to the lack of clear anatomical boundaries, was simple given the clear tumor margins. In summary, the microscopic aspect of the tumor was atypical of a high-grade glioma and more closely resembled a brain metastasis. The intraoperative histopathology, however, suggested a malignant glioma.

Postoperative MRI showed a complete resection of the contrast enhancing tumor. The patient recovered from surgery without new neurological deficits. An initial histological diagnosis of glioblastoma World Health Organization (WHO) grade IV, isocitrate dehydrogenase (IDH) wild type was made. Chemoradiotherapy with 54 Gy to the tumor region and six cycles of temozolomide were administered. The patient returned to full-time employment and reported no recurrence of speech disturbances or memory impairment.

Ultimately, the diagnosis was reversed from a glioblastoma WHO grade IV glioma to the final histological diagnosis based on the molecular characteristics of the tumor. The therapy had been adapted accordingly, and the further course of the disease was monitored by MRI. No recurrence was observed at 6 months after surgery.

Magnetic resonance imaging (MRI) showed a space-occupying intra-axial lesion of the left temporal lobe (Figs. 1, 2 and 3). On the T2-weighted images, the lesion appeared clearly demarcated and showed a predominantly hyperintense signal (Fig. 1a, b, arrow). In the center there were areas of homogeneous hypointense signal (Fig. 1b, arrowhead). On T1-weighted images, the lesion appeared hypointense (Fig. 2a, b, arrow). After administration of gadolinium (Gd), the lesion showed large areas, predominantly in the upper part of the lesion, with clear and homogeneous but not pronounced enhancement (Fig. 2c, d, arrow). Especially the lower part of the lesion showed no contrast enhancement (Fig. 2d, arrowhead). On diffusion-weighted MR images (b-value: 1000), the lesion showed signs of restricted diffusion (Fig. 3a, arrow). Note the central and well-demarcated signal loss (Fig. 3a, arrowhead). This area within the lesion (Fig. 3b, arrow) also appeared hypointense on T2*-weighted images (Fig. 3b, arrowhead). This area may correspond to either local calcification or intralesional hemorrhage. We could not reliably distinguish the two on the basis of the MR images. Unfortunately, we did not perform a preoperative computed tomography (CT) scan.

Hematoxylin and eosin staining of the formaldehyde-fixed and paraffin-embedded biopsy material revealed a pleomorphic glial tumor with necroses and microvascular proliferations (Fig. 4a), scattered mitotic spindles (Fig. 4b) and calcifications (Fig. 4c). Immunohistochemistry showed positivity for glial fibrillary acidic protein (GFAP), oligodendrocyte transcription factor (Olig2), and a retained nuclear expression of ATRX (Fig. 5a–e). CD34 was negative except for individual tumor cells (Fig. 5d). The proliferation marker Ki-67 was found to be positive in up to 10% of the tumor nuclei (Fig. 5e). Based on these features the initial diagnosis was glioblastoma WHO grade IV

Differential diagnoses included high-grade gliomas, astrocytoma, oligodendroglioma, diffuse pediatric-type high-grade glioma, H3-wildtype and IDH-wildtype, diffuse hemispheric glioma, H3 G34-mutant, and some rare neuroectodermal tumors with a diffuse growth pattern. These differential diagnoses are characterized by pleomorphic tumor cells with broad morphological overlaps. Therefore, additional molecular testing was required [1]. Methylation analysis is a fast and cost-efficient way to molecularly distinguish these entities [25]. Glioblastomas are characterized by a distinct methylation and genomic instability with a typical combination of a chromosome 7 gain and a chromosome 10 loss [1]. Astrocytomas and oligodendrogliomas are defined as having pathological hotspot isocitrate dehydrogenase (IDH) mutations [1]. Additionally, oligodendrogliomas show a combined loss of the chromosome arms 1p/19q. Diffuse hemispheric gliomas, H3 G34 mutant, have mutations of the histone H3-3A gene and a characteristic methylation profile [1]. Diffuse pediatric-type high-grade glioma, H3-wildtype and IDH-wildtype, lack these mutations but have a characteristic methylation profile [1]. Additionally, these tumors are frequently associated with previous brain irradiation and constitutional mismatch repair deficiency syndromes [26]. As the morphological appearance of these tumors is unspecific, molecular pathology was initiated.

Molecular testing showed a TP53 loss of function mutation, a common finding in high-grade gliomas. Wild-type alleles were found in the IDH and histone H3 genes. The copy number profile revealed signs of genomic instability with gains of genomic material on several chromosomes including chromosome 7 and chromothripsis on chromosome 10. A combined loss of the chromosome arms 1p/19q was not found. Next, an 850k methylation array analysis was performed. Classification with the Heidelberg brain tumor classifier version 12.5 failed to generate a match with the established methylation classes [25]. Unexpectedly, the highest scores were associated with methylation classes featuring low-grade neuroectodermal tumors, including ganglioglioma and polymorphous low-grade neuroepithelial tumor of the young (PLNTY). The RNA sequencing identified a FGFR2::CTNNA3 fusion. This molecular aberration has so far only been observed in PLNTYs [27].