Pilomyxoid astrocytoma: neuroimaging with clinicopathologic correlates in 4 cases followed over time

Pediatric Cerebellar Pilomyxoid Astrocytoma: Clinical and Radiological Findings in Three Cases

Pilomyxoid astrocytomas (PMA) is a particular form of glial tumors distinct from pilocytic astrocytomas (PA). On the last 2016 WHO classification for CNS tumours, no definite grade assignment was proposed for these lesions. They may be more aggressive with a different clinical course compared to PA due to their greater propensity for local recurrence and cerebrospinal dissemination. Most cases arise from the hypothalamic region. Only few studies reported cerebellar localization of the lesion. We report 3 pediatric cases treated for pediatric PMA of the posterior fossa. Clinical, radiological, and prognostic features were reviewed. The age of our patients was between 1 and 9 years old. Signs of intracranial hypertension were found in all patients. One of them presented an increased head circumference and the 2 others had a cerebellar syndrome. Brain CT-scan and MRI displayed a large wellcircumscribed intra-axial solid and cystic posterior fossa tumor. Total surgical resection was performed for all tumors. After a 2 years follow up, no signs of recurrence were noticed. In the literature, PMA been reported with overwhelming majority in children aged between 2 months and 4 years. Despite of many pathological similarities with PAs, PMAs have some specific features in histology, leading to their identification as independent type of glioma. Radiological differential diagnosis between PMAs and Pas can be made using arterial spin labeling imaging, which shows low perfusion parameters in PAs. Clinical and radiological follow up are mandatory do to different natural history and higher rates of local recurrence of this tumor compared to PA. Prognosis is favorable when complete surgical exeresis is possible.

Recent Progress in the Pathology and Genetics of Pilocytic and Pilomyxoid Astrocytomas

Pilocytic and pilomyxoid astrocytomas are some of the most common gliomas in children and young adults. These gliomas are indolent neoplasms with long overall survival probability. The genetic characteristics of these neoplasms are well known, and our deepened understanding of their associated molecular alterations has led to the development of novel treatment strategies and approaches. Currently, we can account for some of the unusual behavior, such as oncogene-induced senescence, associated spontaneous regression, anaplastic transformation, and cerebrospinal dissemination, of these gliomas. Nevertheless, enigmatic issues continue to surround these chronic tumors. Here, we review the classical and uncommon clinical pathological and genetic features of these indolent gliomas.

Suprasellar pilocytic astrocytoma in an adult with hemorrhage and leptomeningeal dissemination: case report and review of literature

Pilocytic astrocytoma (PA) is a low-grade tumor. It has an excellent prognosis after total resection. Leptomeningeal dissemination and hemorrhage are very rare to be associated with PA and lead to unfavorable prognosis. A 35-year-old man was diagnosed with a hemorrhagic suprasellar PA in 2006. Subsequent examination in 2007 revealed another large subdural hemorrhagic lesion in the sacral region, which proved to be PA by histopathologic assessment. Other leptomeningeal foci were discovered mainly at the craniocervical junction. The patient underwent subtotal resection and received chemotherapy with disease control for 7 years. Progression of the disseminated disease has recently occurred; however, the patient is still alive with stable disease after radiotherapy. The radiological features, management, and relevant literature are also presented. Our report heightens the awareness of PA in the adult population and the importance of close surveillance for the leptomeningeal spread, especially for sellar region tumors.

Cerebellar pilomyxoid astrocytoma

Pilomyxoid astrocytomas (P.M.A) are new class of Pilocytic Astrocytoma (P.A.) which typically have their origin in hypothalamus and chiasmatic region. There are very few case reports of PMAs arising from cerebellum. Their imaging features are similar to PA but they behave more aggressively than PA. The authors report a case of 10 year old male child who presented with right cerebellar tumour diagnosed as PMA on histopathology.

A rare case of multicystic disseminated astrocytoma with pilomyxoid characteristics in a 4-year-old child

Pilomyxoid astrocytomas are a more aggressive variant of pilocytic astrocytoma. Over the last 14 years, there has been increasing evidence to suggest that these tumours are distinct pathological entities to pilocytic astrocytomas. Radiological features of these tumours are slowly emerging in the neuroradiological literature. We report a unique radiological appearance of a multicystic, disseminated astrocytoma with pilomyxoid characteristics presenting in a 4-year-old boy and highlight the importance of considering this diagnosis with similar imaging.

Differential imaging characteristics and dissemination potential of pilomyxoid astrocytomas versus pilocytic astrocytomas

INTRODUCTION

Pilomyxoid astrocytoma (PMA) is a rare WHO grade II tumor occurring most often in young children. PMA is associated with worse outcome as compared to the pathologically related pilocytic astrocytoma (PA). The radiological differentiation of PMAs from PAs is challenging. Furthermore, it is not completely clarified whether PMA is associated with a higher rate of cerebrospinal fluid (CSF) dissemination in the youngest pediatric population as compared to PA. The aim of our study was firstly to compare imaging features of these tumors and, secondly, to evaluate the occurrence of CSF dissemination.

METHODS

The study population included 15 children with PMA and 32 children with PA. The initial MRI and CT scans from the time of the diagnosis were retrospectively analyzed according to standardized criteria and the findings compared between the two tumor types. Furthermore, we also compared the occurrence of imaging evidences of CSF dissemination.

RESULTS

PMAs showed less frequently cystic components (p = 0.03) and never had large tumor cysts. Gadolinium enhancement of PMAs was more frequently homogeneous (p = 0.006). PMAs appeared to show more often intratumoral hemorrhages (p = 0.047). Within the subgroup of children <6 years of age, the PMA histology tended to have a larger effect on the occurrence of CSF dissemination than the age (p = 0.05 vs. 0.12).

CONCLUSION

Some imaging features like enhancement pattern or presence of cysts or hemorrhage may help differentiating these low-grade gliomas. Our results confirm previous scarce data suggesting a higher rate of CSF dissemination in PMAs, even in the youngest patient population.

Pilomyxoid Astrocytoma (PMA) Shows Significant Differences in Gene Expression vs. Pilocytic Astrocytoma (PA) and Variable Tendency Toward Maturation to PA

Pilomyxoid astrocytomas (PMAs) manifest a more aggressive clinical course than pilocytic astrocytomas (PAs). Development of effective therapies demands a better biological understanding of PMA. We first conducted gene expression microarray analysis of 9 PMA and 13 PA from infra- and supratentorial sites. Unsupervised hierarchical clustering analysis demonstrated that tumors are grouped according to anatomic site, not diagnosis. Gene expression profiles were then contrasted between eight PMAs and six PAs, all supratentorial/hypothalamic/chiasmal. Clinical outcome of PMAs varied, with four out of four patients with diencephalic syndrome succumbing to disease, one of whom showed bulky metastatic leptomeningeal spread at autopsy, with bimodal maturation to PA in some areas and de-differentiation to glioblastoma in others. A surviving child has undergone multiple surgical debulking, with progressive maturation to PA over time. Ontology-enrichment analysis identified overexpression in PMAs of extracellular matrix and mitosis-related genes. Genes overexpressed in PMA vs. PA, ranked according to fold-change, included developmental genes H19, DACT2, extracellular matrix collagens (COL2A1; COL1A1) and IGF2BP3 (IMP3), the latter previously identified as an adverse prognostic factor in PMA and PA.

Pilomyxoid astrocytoma of the brainstem

A pilomyxoid astrocytoma is a recently described tumor that occurs predominantly in the hypothalamic-chiasmatic region and is rarely found elsewhere. It has similar features as pilocytic astrocytomas, but has distinct histological characteristics and a poorer prognosis. A pilomyxoid astrocytoma is an aggressive tumor, and increased awareness is necessary with a suspect case. We present the first case of a pilomyxoid astrocytoma of the brainstem described after the newest World Health Organization classification of central nervous system tumors.

Evaluation of the sellar and parasellar regions

The article reviews the anatomy and imaging evaluation of the sellar and parasellar regions. Both common and uncommon sellar and suprasellar masses are reviewed, focusing on a systematic approach to analysis and when appropriate, differential creation.

Temporal and optic pathway pilomyxoid astrocytoma mimicking dural-based lesion: case report and review of the literature

Pilomyxoid astrocytomas (PMAs) are low-grade tumors that share many common traits with pilocytic astrocytomas. However, PMAs have a more worrisome clinical course, with a higher recurrence rate, lower survival rate, and higher risk of leptomeningeal spread compared to pilocytic tumors. These tumors tend to occur in younger children and are typically located in the area of the optic chiasm or hypothalamus. There are few studies examining the radiographic appearance of these lesions. In this case report, the authors present an unusual radiographic appearance of a PMA in an 11-year-old child. Preoperative images suggested a dural-based, homogenously enhancing lesion coupled with an enlarged optic nerve. Surgery revealed an intraparenchymal lesion of the right temporal lobe. There was hyperintensity on T2 MRI sequences, suggesting infiltration of the tumor along the optic tracts.

Pilomyxoid astrocytoma in cerebellum

Pilomyxoid astrocytoma is a new identified variant type of pilocytic astrocytoma, and typically locates in the hypothalamic and chiasmatic region. Herein, we reported a nine-year-old boy with pilomyxoid astrocytoma in the cerebellum. MRI scanning showed a tumor involved the cerebellar vermis, tonsil, the forth ventricle and brainstem. It was homogeneous isointensity on T1WI, relative hyper-intensity on T2WI, hyper-intensity on fluid attenuated inversion recovery (FLAIR) images, and uniform enhancement on contrast T1WI. The tumor was sub-totally removed and was proved histologically to be pilomyxoid astrocytoma. Follow-up at the 5th month, MRI showed the residual tumor enlarged at the brainstem. The patient survived 10 months after the operation, and finally died of respiration failure resulting from brainstem dysfunction.

Pilomyxoid astrocytoma of the cerebellum

Pilomyxoid astrocytomas (PMAs) are low-grade (WHO Grade II) tumors for which the imaging features are similar to pilocytic astrocytomas (PAs), but for which histological features and the clinical course differ. They are classified as a variant of PA. They have only been recently recognized, and they behave more aggressively than PAs. Most cases occur in the hypothalamic-chiasmatic area, although they may be located in any part of the neuraxis. Posterior fossa PMAs are very rare. The authors report a case of a 2-year-old girl with cerebellar PMA.

Pilomyxoid astrocytoma of the cervical spinal cord in a child with rapid progression into glioblastoma: case report and literature review

INTRODUCTION

Pilomyxoid astrocytoma (PMA) is a recently described glial tumor with similarities to pilocytic astrocytomas, yet with distinct histopathological characteristics and a more aggressive behavior. It occurs predominantly in the hypothalamic/chiasmatic region. Only four patients with spinal cord PMA have been reported in the pediatric population. The 2007 WHO Working Group recognized PMA as a new variant and recommended an assignment to WHO grade II.

OBJECTIVE

The purpose of this paper was to report a rare location, address the aggressive behavior and rapid progression, and based on the specific patient, to review the literature and discuss current treatment strategies.

CASE PRESENTATION

A 12-year-old girl presented with motor and sensory deficits of the left side as well as gait disturbance. Imaging revealed an intramedullary tumor extending from C2 to C7. The patient improved impressively after surgical resection. Histopathological findings were consistent with PMA. Three months later, the patient presented with rapid neurological deterioration. Histopathology after the second operation was consistent with glioblastoma. The outcome was fatal 12 months after initial diagnosis, despite adjuvant therapy.

CONCLUSIONS

This is the fifth pediatric spinal cord PMA in literature. Furthermore, it is the only documented patient with rapid recurrence and progression within 3 months into a glioblastoma. The question of a sampling error affecting initial pathology is raised. Based on contemporary literature data, we discuss the further treatment options, as there are no guidelines yet. Efforts towards registries should be encouraged, as the documentation of PMA might lead to more evidence based treatment strategies.

A multivariate analysis of factors determining tumor progression in childhood low-grade glioma: a population-based cohort study (CCLG CNS9702)

The purpose of this study was to identify risk factors for the progression of low-grade glioma in children from a large population-based cohort. Patient and tumor details of a national cohort of children with low-grade glioma, recruited into an international multidisciplinary clinical strategy, were subjected to univariate and multivariate analyses of progression-free survival and overall survival. From the cohort of 798 patients, 639 patients were eligible, with a median age 6.71 years (0.26-16.75 years); 49% were males; 15.9% had neurofibromatosis type 1, 63.7% pilocytic astrocytoma, 5.9% fibrillary astrocytoma, 4.2% mixed neuronal-glial tumors, and 3.6% others; 21.1% were diagnosed clinically. Anatomically implicated were 31.6% cerebellum, 24.6% chiasma/hypothalamus, 16.0% cerebral hemispheres, 9.9% brain stem, 6.1% other supratentorial midline structures, 5.9% optic nerve only, 4.5% spinal cord, and 1.4% others. The 5-year overall survival and progression-free survival in the whole cohort were 94.6% and 69.4%, respectively. There was a significant association between age and site (P < .001) and extent of tumor resection and site (P < .001). Multivariate analysis identified young age, fibrillary astrocytoma, and extent of surgical resection as significant independent risk factors for progression. Hypothalamic/chiasmatic tumors demonstrated the most sustained tendency to progress. In conclusion, the influence of age and anatomical site upon the risk of tumor progression suggests that these factors strongly influence tumor behavior for the majority of pilocytic tumors. Age <1 year and 1-5 years, fibrillary histology, completeness of resection, and chiasmatic location are candidates for stratification in future studies.

Imaging characteristics of pilomyxoid astrocytomas in comparison with pilocytic astrocytomas

PURPOSE

Pilomyxoid astrocytoma (PMA) is a recently described astrocytic tumor that has been previously diagnosed as pilocytic astrocytoma (PA). The purpose of this study was to describe the imaging features of PMAs in comparison with PAs.

MATERIALS AND METHODS

We retrospectively reviewed CT/MR images and medical records of 10 patients with PMA and 38 patients with PA. The mean ages of patients with PMA and PA were 10 and 15 years, respectively. Imaging features including location, composition, enhancement pattern, presence of calcification, hemorrhage, and leptomeningeal dissemination were compared in patients with two tumor types.

RESULTS

Six PMAs (60%) occurred at the suprasellar area and the cerebellum was the most common (45%) site of PA. Solid component was dominant in eight PMAs (80%) and in 19 PAs (50%). All of the PMAs containing solid mass (n=8) included non-enhancing portion while 12/37 (32%) PAs included non-enhancing solid portion (p<0.05). Leptomeningeal dissemination was noted in five PMAs (50%) and one PA (3%) (p<0.05). Other imaging findings were not significantly different.

CONCLUSION

A younger age, more frequent occurrence at the suprasellar area, mainly solid mass containing non-enhancing portion, and more frequent leptomeningeal dissemination are helpful differential features of PMAs as compared to PAs.

Pilomyxoid astrocytoma: expanding the imaging spectrum

BACKGROUND AND PURPOSE

Pilomyxoid astrocytoma (PMA) is a recently described variant of pilocytic astrocytoma (PA) with unique clinical and histopathologic characteristics. Because the histopathology of PMA is distinct from that of PA, we hypothesized that PMAs would display distinctive imaging characteristics. We retrospectively reviewed the imaging findings in a large number of patients with PMA to identify these characteristics.

MATERIALS AND METHODS

CT and MR images, pathology reports, and clinical information from 21 patients with pathology-confirmed PMA from 7 institutions were retrospectively reviewed. CT and MR imaging findings, including location, size, signal intensity, hemorrhage, and enhancement pattern, were tabulated.

RESULTS

Patients ranged in age from 9 months to 46 years at initial diagnosis. Sex ratio was 12:9 (M/F). Twelve of 21 (57%) tumors were located in the hypothalamic/chiasmatic/third ventricular region. Nine (43%) occurred in other locations, including the parietal lobe (2/21), temporal lobe (2/21), cerebellum (2/21), basal ganglia (2/21), and fourth ventricle (1/21). Ten (48%) tumors showed heterogeneous rim enhancement, 9 (43%) showed uniform enhancement, and 2 (9%) showed no enhancement. Five (24%) masses demonstrated intratumoral hemorrhage.

CONCLUSION

This series expands the clinical and imaging spectrum of PMA and identifies characteristics that should suggest consideration of this uncommon diagnosis. One third of patients were older children and adults. Almost half of all tumors were located outside the typical hypothalamic/chiasmatic region. Intratumoral hemorrhage occurred in one quarter of patients. PMA remains a histologic diagnosis without definitive imaging findings that distinguish it from PA.