Uncommon pediatric tumors of the posterior fossa: pathologic and molecular features

Transcallosal and endoscopic hybrid approach to a rare entity of pediatric intraventricular tumors-cribriform neuroepithelial tumor: a case report and literature review

PURPOSE

Cribriform neuroepithelial tumor (CRINET) is a provisional category of intraventricular tumors, sharing similarities with AT/RTs, and there is a lack of data about its pathology, prognosis, and surgical approaches in the literature. We have been challenged to describe the surgical approach to a rare case of CRINET and describe the intraoperative features since none has been described before. Surgical resection and chemotherapy hold a great importance of favorable prognosis.

METHODS

Twenty-month-old male with intraventricular tumor underwent transcallosal intraventricular tumor resection and endoscopic intraventricular second look stages. The tumor was initially considered choroid plexus carcinoma and histopathological results pointed CRINET. The patient also received Ommaya reservoir for intrathecal chemotherapy employment. The patient's preoperative and postoperative MRI scans and tumor's pathological features are described with a brief history of the disease in the literature.

RESULTS

Lack of SMARCB1 gene immunoreactivity and presence of cribriform non-rhabdoid trabecular neuroepithelial cells led to the CRINET diagnosis. The surgical technique helped us to approach directly into the third ventricle and perform total resection and intraventricular lavage. The patient recovered without any perioperative complications and is consulted pediatric oncology for further treatment planning.

CONCLUSION

With our limited knowledge on the matter, our presentation may provide an inside to the course and progress of the CRINET as a very rare tumor and may help to set a basis for future investigations focused on its clinical and pathological features. Long courses of follow-up periods are required for establishing treatment modules and assessing the responses to surgical resection techniques and chemotherapy protocols.

An extracranial CNS presentation of the emerging "intracranial" mesenchymal tumor, FET: CREB-fusion positive

A novel histomolecular tumor, the "intracranial mesenchymal tumor (IMT), FET::CREB fusion-positive", has recently been identified and added to the 2021 World Health Organization Classification of Tumors of the Central Nervous System. One of the essential diagnostic criteria defined in this classification is the intracranial location of the tumor. Herein, we report a spinal case of IMT with a classical EWSR1::CREM fusion. We compare its clinical, histopathological, immunophenotypical, genetic and epigenetic features with those previously described in IMT, FET::CREB fusion-positive. The current case presented histopathological (epithelioid morphology with mucin-rich stroma, and expression of EMA and desmin), radiological (an extraparenchymal lobulated mass without dural tail), genetic (fusion implicating the EWSR1 and CREM genes), and epigenetic (DNA-methylation profiling) similarities to previously reported cases. This case constitutes the third "extracranial" observation of an IMT. Our results added data suggesting that the terminology "IMT, FET::CREB fusion-positive" is provisional and that further series of cases are needed to better characterize them.

The semisitting position in pediatric neurosurgery: pearls and pitfalls of a 10-year experience

OBJECTIVE

The authors sought to investigate the pearls and pitfalls of using the semisitting position in pediatric neurosurgery, with special focus on related morbidity and surgical practicability.

METHODS

All pediatric cases at a single institution were evaluated retrospectively. Those patients who underwent procedures in the semisitting position between December 2010 and December 2020 were included in the final analysis. Results were compared with all children who underwent surgery in the prone position for posterior fossa lesions within the same time frame.

RESULTS

A total of 42 posterior fossa surgeries were performed in 38 children in the semisitting position between December 2010 and December 2020. The mean patient age at the time of surgery was 8.9 years (range 13 months-18 years). The data of 24 surgeries performed in the prone position in 22 children during the same time frame were analyzed in comparison. Three children (7.9%) were diagnosed with a persistent foramen ovale preoperatively. The surgery was completed in all cases. The incidence of venous air embolism (VAE) was 11.9%. There was no VAE-related hemodynamic instability, infarction, or death. Endoscopic techniques were applied safely in 14 cases (33.3%). Postoperative pneumocephalus occurred significantly more frequently in patients who had undergone procedures in the semisitting position (p < 0.05), but without the need for intervention. During 1 surgery (2.4%), the patient experienced a postoperative skull fracture and epidural bleeding due to the skull clamp application. Clinical status of the patients immediately after surgery was improved or stable in 33 of the 42 surgeries (78.6%) performed in the semisitting position.

CONCLUSIONS

With attentive performance and an experienced surgical team, the semisitting position is a safe option for posterior fossa surgery in the pediatric population. With a comparable complication profile, the semisitting position offers excellent anatomical exposure, which is ideal for the application of endoscopic visualization. Careful skull clamp application and appropriate monitoring are highly recommended.

Pediatric rosette-forming glioneuronal tumor of the septum pellucidum

Rosette-forming glioneuronal tumor (RGNT) is a rare tumor entity which has been reported mainly occurring in the fourth ventricle. It has been described as a benign lesion with limited extension into surrounding structures, including the cerebellar vermis, midbrain, and cerebral aqueduct. More recently, few cases involving also other midline structures have been documented as well. Here, we report about diagnosis and treatment of RGNT in the septum pellucidum in a pediatric patient which has not been described previously. A 7-year-old boy had a 3-week history of headache. Magnetic resonance imaging showed a solid mass in the septum pellucidum accompanied by hydrocephalus. The tumor was resected via a transcortical approach. Histological examination revealed the typical findings of a RGNT. At 2-year follow-up, there was no tumor recurrence, and clinical outcome was unremarkable. RGNT has to be considered in the differential diagnosis of pediatric midline tumors also outside of the fourth ventricle. Surgical resection is the first-line therapy which may result in beneficial outcome in the long term. The role of adjuvant therapy needs further definition since due to the rarity of this tumor entity, available data is very limited.

Rosette-forming Glioneuronal Tumor in the Optic Pathway of a Child

Rosette-forming glioneuronal tumor is a rare World Health Organization grade I neoplasm, primarily involving the posterior fossa. Most cases have been reported in young adults. Although maximal surgical resection is advocated, a precise treatment modality is yet to be established. We describe an unusual presentation of rosette-forming glioneuronal tumor occurring in the optic pathway in a child. As the site of the tumor was not amenable to resection, he underwent radiotherapy and is currently well on follow-up.

Beyond the Blood: CSF-Derived cfDNA for Diagnosis and Characterization of CNS Tumors

Genetic data are rapidly becoming part of tumor classification and are integral to prognosis and predicting response to therapy. Current molecular tumor profiling relies heavily on tissue resection or biopsy. Tissue profiling has several disadvantages in tumors of the central nervous system, including the challenge associated with invasive biopsy, the heterogeneous nature of many malignancies where a small biopsy can underrepresent the mutational profile, and the frequent lack of obtaining a repeat biopsy, which limits routine monitoring to assess therapy response and/or tumor evolution. Circulating tumor, cell-free DNA (cfDNA), has been proposed as a liquid biopsy to address some limitations of tissue-based genetics. In cancer patients, a portion of cfDNA is tumor-derived and may contain somatic genetic alterations. In central nervous system (CNS) neoplasia, plasma tumor-derived cfDNA is very low or absent, likely due to the blood brain barrier. Interrogating cfDNA in cerebrospinal fluid (CSF) has several advantages. Compared to blood, CSF is paucicellular and therefore predominantly lacks non-tumor cfDNA; however, patients with CNS-limited tumors have significantly enriched tumor-derived cfDNA in CSF. In patients with metastatic CNS disease, mutations in CSF cfDNA are most concordant with the intracranial process. CSF cfDNA can also occasionally uncover additional genetic alterations absent in concurrent biopsy specimens, reflecting tumor heterogeneity. Although CSF is enriched for tumor-derived cfDNA, absolute quantities are low. Highly sensitive, targeted methods including next-generation sequencing and digital PCR are required to detect mutations in CSF cfDNA. Additional technical and bioinformatic approaches also facilitate enhanced ability to detect tumor mutations in CSF cfDNA.

Clinicopathologic and molecular features of intracranial desmoplastic small round cell tumors

Desmoplastic small round cell tumors (DSRCTs) are highly aggressive sarcomas that most commonly occur intra-abdominally, and are defined by EWSR1-WT1 gene fusion. Intracranial DSRCTs are exceptionally rare with only seven previously reported fusion-positive cases. Herein, we evaluate the clinical, morphologic, immunohistochemical and molecular features of five additional examples. All patients were male (age range 6-25 years; median 11 years), with four tumors located supratentorially and one within the posterior fossa. The histologic features were highly variable including small cell, embryonal, clear cell, rhabdoid, anaplastic and glioma-like appearances. A prominent desmoplastic stroma was seen in only two cases. The mitotic index ranged from <1 to 12/10 HPF (median 5). While all tumors showed strong desmin positivity, epithelial markers such as EMA, CAM 5.2 and other keratins were strongly positive in only one, focally positive in two and negative in two cases. EWSR1-WT1 gene fusion was present in all cases, with accompanying mutations in the TERT promoter or STAG2 gene in individual cases. Given the significant histologic diversity, in the absence of genetic evaluation these cases could easily be misinterpreted as other entities. Desmin immunostaining is a useful initial screening method for consideration of a DSRCT diagnosis, prompting confirmatory molecular testing. Demonstrating the presence of an EWSR1-WT1 fusion provides a definitive diagnosis of DSRCT. Genome-wide methylation profiles of intracranial DSRCTs matched those of extracranial DSRCTs. Thus, despite the occasionally unusual histologic features and immunoprofile, intracranial DSRCTs likely represent a similar, if not the same, entity as their soft tissue counterpart based on the shared fusion and methylation profiles.

Pontine tumor in a neonate: case report and analysis of the current literature

Tumors of the central nervous system represent the largest group of solid tumors found in pediatric patients. Pilocytic astrocytoma is the most common pediatric glioma, mostly located in the posterior fossa. The majority of brainstem tumors, however, are classified as highly aggressive diffuse intrinsic pontine gliomas (DIPGs) and their prognosis is dismal.The authors report on the case of a neonate in whom MRI and neuropathological assessment were used to diagnose DIPG. Before initiation of the planned chemotherapy, the tumor regressed spontaneously, and the newborn exhibited a normal neurological development. Meanwhile, Illumina Human Methylation450 BeadChip analysis reclassified the tumor as pilocytic astrocytoma of the posterior fossa.In conclusion, the authors advocate not initiating immediate intensive therapy in newborns with brain tumors, even with classical appearance of a DIPG; rather, they would like to encourage a biopsy to define the best individual therapeutic approach and avoid ineffective chemotherapy.

SMARCB1-deficient Tumors of Childhood: A Practical Guide

The SMARCB1 gene ( INI1, BAF47) is a member of the SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complex, involved in the epigenetic regulation of gene transcription. SMARCB1 acts as a tumor suppressor gene, and loss of function of both alleles gives rise to SMARCB1-deficient tumors. The prototypical SMARCB1-deficient tumor is the malignant rhabdoid tumor (MRT) which was first described in the kidney but also occurs in soft tissue, viscera, and the brain (where it is referred to as atypical teratoid rhabdoid tumor or AT/RT). These are overwhelmingly tumors of the very young, and most follow an aggressive and ultimately lethal course. Morphologically, most but not all contain a population of "rhabdoid" cells, which are large cells with abundant cytoplasm, perinuclear spherical inclusions, and eccentric vesicular nuclei with large inclusion-like nucleoli. MRT immunohistochemistry reveals complete loss of SMARCB1 nuclear expression, and molecular analysis confirms biallelic SMARCB1 inactivation in the vast majority. Rare AT/RTs have loss of SMARCA4, another SWI/SNF member, rather than SMARCB1. With the widespread adoption of SMARCB1 immunohistochemistry, an increasing number of SMARCB1-deficient tumors outside of the MRT-AT/RT spectrum have been described. In addition to MRT and AT/RT, pediatric tumors with complete loss of SMARCB1 expression include cribriform neuroepithelial tumor, renal medullary carcinoma, and epithelioid sarcoma. Tumors with variable loss of SMARCB1 expression include subsets of epithelioid malignant peripheral nerve sheath tumor, schwannomas arising in schwannomatosis, subsets of chordomas, myoepithelial carcinomas, and sinonasal carcinomas. Variable and reduced expression of SMARCB1 is characteristic of synovial sarcoma. In this review, the historical background, clinical characteristics, morphology, immunohistochemical features, and molecular genetics most germane to these tumors are summarized. In addition, familial occurrence of these tumors (the rhabdoid tumor predisposition syndrome) is discussed. It is hoped that this review may provide practical guidance to pathologists encountering tumors that have altered expression of SMARCB1.

Cribriform neuroepithelial tumor: molecular characterization of a SMARCB1-deficient non-rhabdoid tumor with favorable long-term outcome

Rhabdoid phenotype and loss of SMARCB1 expression in a brain tumor are characteristic features of atypical teratoid/rhabdoid tumors (ATRT). Rare non-rhabdoid brain tumors showing cribriform growth pattern and SMARCB1 loss have been designated cribriform neuroepithelial tumor (CRINET). Small case series suggest that CRINETs may have a relatively favorable prognosis. However, the long-term outcome is unclear and it remains uncertain whether CRINET represents a distinct entity or a variant of ATRT. Therefore, 10 CRINETs were clinically and molecularly characterized and compared with 10 ATRTs of each of three recently described molecular subgroups (i.e. ATRT-TYR, ATRT-SHH and ATRT-MYC) using Illumina Infinium HumanMethylation450 arrays, FISH, MLPA, and sequencing. Furthermore, outcome was compared to a larger cohort of 27 children with ATRT-TYR. Median age of the 6 boys and 4 girls harboring a CRINET was 20 months. On histopathological examination, all CRINETs demonstrated a cribriform growth pattern and distinct tyrosinase staining. On unsupervised cluster analysis of methylation data, all CRINETs examined exclusively clustered within the ATRT-TYR molecular subgroup. As ATRT-TYR, CRINETs mainly showed large heterozygous 22q deletions (9/10) and SMARCB1 mutations of the other allele. In two patients, SMARCB1 mutations were also present in the germline. Estimated mean overall survival in patients with CRINETs was 125 months (95% confidence interval 100-151 months) as compared to only 53 (33-74) months in patients with ATRTs of the ATRT-TYR subgroup (Log-Rank P < 0.05). In conclusion, CRINET represents a SMARCB1-deficient non-rhabdoid tumor, which shares molecular similarities with the ATRT-TYR subgroup but has distinct histopathological features and favorable long-term outcome.