505 lines
34 KiB
Markdown
505 lines
34 KiB
Markdown
---
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title: "Pilomyxoid Astrocytoma"
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docid: "7208af53-1e09-411a-951d-1ea7bd40be53"
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authors:
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- key: "47381de4-c9fd-4999-8dd0-1808cd72db6b"
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value: "Luke L. Linscott, MD"
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- key: "5cff4116-3654-4b3a-bb75-5ebe0b8c9850"
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value: "Anne G. Osborn, MD, FACR"
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breadcrumbs:
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-
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name: "Pediatrics"
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slug: "pediatrics"
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treeNodeId: "a915965c-d436-44cf-ae65-2f22e7246ea4"
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-
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name: "Diagnosis"
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slug: "diagnosis"
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treeNodeId: "2b5cea64-a083-489e-ac0c-ec14ba059026"
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name: "Pediatric Neuroradiology"
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slug: "pediatric-neuroradiology"
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treeNodeId: "d0eb8f4a-e769-43dd-896c-8c9c27ce8759"
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-
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name: "Brain"
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slug: "brain"
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treeNodeId: "feaaadba-649b-4f0a-9aad-9188a8f9926a"
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-
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name: "Pathology-Based Diagnoses"
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slug: "pathology-based-diagnoses"
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treeNodeId: "2d26053f-23a7-4062-bf35-a93775ae1209"
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-
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name: "Neoplasms"
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slug: "neoplasms"
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treeNodeId: "753a271a-f539-4662-a805-059486e3c267"
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name: "Pilomyxoid Astrocytoma"
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slug: "pilomyxoid-astrocytoma"
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treeNodeId: null
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category: "Pediatrics"
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cmeTopicId: "34d90a10-f275-4f55-922b-0f89af8cba2b"
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documentVersionId: "614c8777-1be1-46f0-acce-655cdd80afc3"
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imageCount: 29
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lastUpdated: "02/09/24"
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pageDescription: "Pilomyxoid Astrocytoma"
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pageKeywords: "Pediatrics, Diagnosis, Pediatric Neuroradiology, Brain, Pathology-Based Diagnoses, Neoplasms, Pilomyxoid Astrocytoma"
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pageTitle: "Pilomyxoid Astrocytoma | STATdx"
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enhancedTitle: "Pilomyxoid Astrocytoma"
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type: "DX"
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references: true
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breadcrumbs:
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- "Pediatrics"
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- "Diagnosis"
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- "Pediatric Neuroradiology"
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- "Brain"
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- "Pathology-Based Diagnoses"
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- "Neoplasms"
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- "Pilomyxoid Astrocytoma"
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---
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# KEY FACTS
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- ## Terminology
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- Pilomyxoid astrocytoma (PMA): More aggressive, myxoid variant of pilocytic astrocytoma (PA)
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- High risk of local recurrence, CSF dissemination
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- ## Imaging
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- 60% suprasellar (large, bulky, H-shaped mass in hypothalamus/optic chiasm, medial temporal lobes)
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- 40% outside diencephalon (hemisphere, ventricles)
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- Grossly well circumscribed, little/no edema
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- Enhances strongly
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- 20% show intratumoral hemorrhage
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- ## Top Differential Diagnoses
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- PA
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- High-grade glioma
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- Germinoma
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- ## Pathology
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- WHO grade 2 (typical PA is WHO grade 1)
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- ## Clinical Issues
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- Typical: Infants, young children (< 4 years)
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- Less common: Older children, young adults
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- 5-10% of cases initially diagnosed as PAs may actually be PMAs
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- Especially if tumor is hemorrhagic, presents in very young child, or shows CSF dissemination
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- ## Diagnostic Checklist
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- Consider PMA if
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- Infant or young child has large/bulky or hemorrhagic H-shaped suprasellar mass
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- Presumed PA in any patient who has atypical imaging (e.g., hemorrhage, metastases)
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# TERMINOLOGY
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- ## Abbreviations
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- Pilomyxoid astrocytoma (PMA)
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- ## Synonyms
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- Myxoid variant of pilocytic astrocytoma (PA)
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- ## Definitions
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- Tumor with monomorphic piloid cells dispersed in mucopolysaccharide-rich matrix
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- More aggressive tumor than PA with high risk of local recurrence, dissemination
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# IMAGING
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- ## General Features
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- ### Best diagnostic clue
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- Infant or young child with large, bulky, H-shaped mass in hypothalamus/optic chiasm, medial temporal lobes
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- ### Location
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- 60% suprasellar
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- Optic chiasm, hypothalamus
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- Extension into adjacent structures is common with larger tumors
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- Deep gray nuclei, temporal lobes, adjacent white matter often involved
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- 40% centered **outside** diencephalon
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- Cerebral hemispheres
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- 2nd most common general location
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- Temporal lobe most common
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- May be purely cortical
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- Less common sites reported
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- Midbrain
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- Cerebellum
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- 4th ventricle
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- Spinal cord
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- ### Size
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- Variable
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- Mean: 4 cm
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- Often large, bulky (up to 12 cm)
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- ### Morphology
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- Grossly well circumscribed
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- ## CT Findings
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- ### NECT
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- Uniform hypodensity most common
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- 20% show intratumoral hemorrhage
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- Hyperdense; mixed hypo-/hyperdense
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- Ca⁺⁺ occurs but uncommon
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- ### CECT
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- Strong, but inhomogeneous enhancement
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- Irregular central nonenhancing area in 1/3
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- ## MR Findings
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- ### T1WI
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- Typical: Uniformly hypointense (almost 2/3 of cases)
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- Less common: Mixed hypo-/hyperintensity (10-15%)
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- Uncommon: Blood-fluid level
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- ### T2WI
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- 70% uniformly hyperintense
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- 15% inhomogeneously hyperintense
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- 10% hypointense center, hyperintense rim
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- ### FLAIR
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- 50% uniformly hyperintense
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- 33% heterogeneously hyperintense
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- Relatively well-demarcated margins
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- Little or no peritumoral edema
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- ### T2* GRE
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- Intratumoral hemorrhage in 20%
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- May be strikingly hypointense
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- ### DWI
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- Typically does not restrict
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- ADC signal in solid component usually significantly ↑ compared to brain parenchyma
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- ### PWI
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- ASL and DSC PWI may help distinguish PMA from PA
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- ASL: Mean tumor:GM cerebral blood flow (CBF) ratio = 1.3 in PMA vs. 0.4 in PA
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- DSC: Relative cerebral blood volume (rCBV) is 2 in PMA vs. 1.5 in PA
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- ### T1WI C+
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- Strong but heterogeneous enhancement
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- 50% heterogeneous (i.e., rim)
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- 40% solid, homogeneous
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- 10% no enhancement
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- Basilar/spinal meningeal enhancement is common and indicates CSF dissemination
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- ## Other Modality Findings
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- MRS
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- ↑ Cho, ↓ Cr and NAA ± lactate
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- Some authors report low-metabolite pattern with ↓ Cho, Cr, NAA
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- ## Imaging Recommendations
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- ### Best imaging tool
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- MR with T1 C+, DWI, T2* (GRE or SWI), MRS
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- ### Protocol advice
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- Thin-section sagittal, coronal pre- and postcontrast T1WI
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- Whole-brain FLAIR
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- Thin-section T2WI through hypothalamus, chiasm
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- GRE or SWI (to look for hemorrhage)
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- Optional: Add DWI, MRS
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# DIFFERENTIAL DIAGNOSIS
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- [Pilocytic Astrocytoma](/document/pilocytic-astrocytoma/7eca92f5-6caa-4300-9afe-1b733b4473b2)
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- Older children (mean age at diagnosis: 6 years)
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- In hypothalamus, typically enhances strongly/uniformly
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- Occasionally calcified
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- Clinically indolent, rarely aggressive
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- PMA usually more hyperintense on T2/FLAIR (mucoid matrix)
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- Hemorrhage, CSF dissemination uncommon
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- Paradoxically aggressive MRS pattern: ↑ Cho, ↓ Cr, ↓ NAA
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- Some PMAs show low metabolite concentrations
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- [High-Grade Glioma (Anaplastic Astrocytoma, Glioblastoma)](/document/glioblastoma/45c3147e-3a1b-4fbf-a626-ed6e99a02ac2)
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- Hemorrhage, necrosis common
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- Hypothalamus rare location
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- Patients usually older
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- May arise from lower grade astrocytoma
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- [Germinoma](/document/germinoma/078b68a2-67de-457e-818a-63655cec95aa)
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- Most often in suprasellar, pineal, or basal ganglia regions
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- Numerous microcysts common
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- Diffusion restriction of solid components reflects high cellularity
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# PATHOLOGY
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- ## General Features
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- ### Etiology
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- Unknown
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- Some tumors demonstrate synaptophysin reactivity, suggesting PMAs may be of mixed glioneuronal origin
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- May also originate from tanycytic cells
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- ### Genetics
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- PMA has significant differences in gene expression vs. PA
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- *H19*, *DACT2*, extracellular matrix collagens, *IGF2BP3*(*IMP3*) overexpressed in PMAs
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- Variable tendencies toward maturation to PA
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- ### Associated abnormalities
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- Few cases associated with neurofibromatosis type 1 have been reported
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- ## Staging, Grading, & Classification
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- WHO grade 2 (PA is WHO grade 1)
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- Grade 3 if anaplastic features
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- Malignant transformation to glioblastoma (grade 4) rare but does occur
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- *MIB1* generally low (1-2%) but higher in anaplastic pleomorphic xanthoastrocytomas
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- ## Gross Pathologic & Surgical Features
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- Large, grossly well-circumscribed mass
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- Necrosis, hemorrhage may be present
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- ## Microscopic Features
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- Lacks classic biphasic pattern seen in PAs
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- Alternating solid and loose areas interspersed with microcysts not seen
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- Rosenthal fibers, eosinophilic granular bodies absent
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- Consists of monomorphic piloid tumor cells
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- Embedded in myxoid (mucopolysaccharide-rich) matrix
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- GFAP (+), vimentin (+)
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- Conspicuous angiocentric growth pattern (perivascular rosettes)
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- Vascular proliferation may be marked
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- Infiltration of tumor cells into adjacent brain common
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- Necrosis rare
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# CLINICAL ISSUES
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- ## Presentation
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- ### Most common signs/symptoms
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- Signs of ↑ intracranial pressure
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- Headache
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- Nausea, vomiting
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- Delayed development
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- Failure to thrive (so-called diencephalic syndrome)
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- Visual disturbances
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- Hypothalamic dysfunction
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- ### Other signs/symptoms
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- Seizures
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- Focal neurologic deficit
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- ## Demographics
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- ### Age
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- Typical: Infants, young children (< 4 years)
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- Less common: Older children, young adults
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- Rare: Middle-aged adult (up to 46 years)
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- ### Sex
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- Slight male predominance (M:F = 4:3)
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- ### Epidemiology
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- Rare; represent < 1% of astrocytomas
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- 5-10% of cases initially diagnosed as PAs may be PMAs, especially if hemorrhage is present or tumor presents in very young child
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- ## Natural History & Prognosis
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- Higher recurrence rate than PA
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- CSF dissemination common
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- Bimodal pattern
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- Can mature to PA
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- May dedifferentiate into GBM
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- ## Treatment
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- Partial resection with adjuvant therapy may prolong survival
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# DIAGNOSTIC CHECKLIST
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- ## Consider
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- PMA if
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- Infant or young child has large/bulky or hemorrhagic suprasellar mass
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- Imaging atypical for PA (i.e., hemorrhage)
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- If PA with repeated recurrences, CSF dissemination, review histopathology and consider PMA
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- ## Image Interpretation Pearls
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- H-shaped suprasellar mass may be PMA
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1af64b07-c8e0-4129-92e0-366b39b94ad3
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## References
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# Selected References
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1. [AlShail E et al: A molecular study of pediatric pilomyxoid and pilocytic astrocytomas: genome-wide copy number screening, retrospective analysis of clinicopathological features and long-term clinical outcome. Front Oncol. 13:1034292, 2023](http://www.ncbi.nlm.nih.gov/pubmed/?term=36860324%5Bpmid%5D)
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1. [Mbekeani JN et al: Pediatric pilomyxoid astrocytoma - ophthalmic and neuroradiologic manifestations. Eur J Ophthalmol. 32(5):2604-14, 2022](http://www.ncbi.nlm.nih.gov/pubmed/?term=34841927%5Bpmid%5D)
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1. [Benson JC et al: Hypothalamic pilomyxoid astrocytoma in a child with lipodystrophy. AJNR Am J Neuroradiol. 42(8):1370-4, 2021](http://www.ncbi.nlm.nih.gov/pubmed/?term=33958332%5Bpmid%5D)
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1. [Gader G et al: Pediatric cerebellar pilomyxoid astrocytoma: clinical and radiological findings in three cases. Asian J Neurosurg. 15(2):262-5, 2020](http://www.ncbi.nlm.nih.gov/pubmed/?term=32656116%5Bpmid%5D)
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1. [Ho CY et al: Differentiation of pilocytic and pilomyxoid astrocytomas using dynamic susceptibility contrast perfusion and diffusion weighted imaging. Neuroradiology. 62(1):81-8, 2020](http://www.ncbi.nlm.nih.gov/pubmed/?term=31676961%5Bpmid%5D)
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1. [He J et al: Posterior fossa pilomyxoid astrocytoma with spontaneous hemorrhage in pediatric patients. Childs Nerv Syst. 34(1):149-53, 2018](http://www.ncbi.nlm.nih.gov/pubmed/?term=28741227%5Bpmid%5D)
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1. [Louis DN et al: The 2016 World Health Organization classification of tumors of the central nervous system: a summary. Acta Neuropathol. 131(6):803-20, 2016](http://www.ncbi.nlm.nih.gov/pubmed/?term=27157931%5Bpmid%5D)
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1. [Wang Z et al: Spontaneous intratumoural and intraventricular haemorrhage associated with a pilomyxoid astrocytoma in the hypothalamic/chiasmatic region. J Clin Neurosci. 33:217-20, 2016](http://www.ncbi.nlm.nih.gov/pubmed/?term=27450285%5Bpmid%5D)
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1. [Alkonyi B et al: Differential imaging characteristics and dissemination potential of pilomyxoid astrocytomas versus pilocytic astrocytomas. Neuroradiology. 57(6):625-38, 2015](http://www.ncbi.nlm.nih.gov/pubmed/?term=25666233%5Bpmid%5D)
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1. [Amarasinghe SG et al: A rare case of multicystic disseminated astrocytoma with pilomyxoid characteristics in a 4-year-old child. Childs Nerv Syst. 31(4):625-9, 2015](http://www.ncbi.nlm.nih.gov/pubmed/?term=25348811%5Bpmid%5D)
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1. [Nabavizadeh SA et al: High accuracy of arterial spin labeling perfusion imaging in differentiation of pilomyxoid from pilocytic astrocytoma. Neuroradiology. 57(5):527-33, 2015](http://www.ncbi.nlm.nih.gov/pubmed/?term=25666232%5Bpmid%5D)
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1. [El Beltagy MA et al: Surgical and clinical aspects of cerebellar pilomyxoid-spectrum astrocytomas in children. Childs Nerv Syst. 30(6):1045-53, 2014](http://www.ncbi.nlm.nih.gov/pubmed/?term=24497195%5Bpmid%5D)
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1. [Kleinschmidt-DeMasters BK et al: Pilomyxoid astrocytoma (PMA) shows significant differences in gene expression vs. pilocytic astrocytoma (PA) and variable tendency toward maturation to PA. Brain Pathol. 25(4):429-40, 2015](http://www.ncbi.nlm.nih.gov/pubmed/?term=25521223%5Bpmid%5D)
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1. [Amirjamshidi A et al: Pilomyxoid astrocytoma. J Neurosurg Pediatr. 11(5):613, 2013](http://www.ncbi.nlm.nih.gov/pubmed/?term=23495811%5Bpmid%5D)
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1. [Bhargava D et al: Occurrence and distribution of pilomyxoid astrocytoma. Br J Neurosurg. 27(4):413-8, 2013](http://www.ncbi.nlm.nih.gov/pubmed/?term=23281683%5Bpmid%5D)
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1. [Lee IH et al: Imaging characteristics of pilomyxoid astrocytomas in comparison with pilocytic astrocytomas. Eur J Radiol. 79(2):311-6, 2011](http://www.ncbi.nlm.nih.gov/pubmed/?term=20619565%5Bpmid%5D)
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1. [Johnson MW et al: Spectrum of pilomyxoid astrocytomas: intermediate pilomyxoid tumors. Am J Surg Pathol. 34(12):1783-91, 2010](http://www.ncbi.nlm.nih.gov/pubmed/?term=21107083%5Bpmid%5D)
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1. [Amatya VJ et al: Clinicopathological and immunohistochemical features of three pilomyxoid astrocytomas: comparative study with 11 pilocytic astrocytomas. Pathol Int. 59(2):80-5, 2009](http://www.ncbi.nlm.nih.gov/pubmed/?term=19154260%5Bpmid%5D)
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1. [Buccoliero AM et al: Occipital pilomyxoid astrocytoma in a 14-year-old girl--case report. Clin Neuropathol. 27(6):373-7, 2008](http://www.ncbi.nlm.nih.gov/pubmed/?term=19130733%5Bpmid%5D)
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1. [Komotar RJ et al: Magnetic resonance imaging characteristics of pilomyxoid astrocytoma. Neurol Res. 30(9):945-51, 2008](http://www.ncbi.nlm.nih.gov/pubmed/?term=18662499%5Bpmid%5D)
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1. [Linscott LL et al: Pilomyxoid astrocytoma: expanding the imaging spectrum. AJNR Am J Neuroradiol. 29(10):1861-6, 2008](http://www.ncbi.nlm.nih.gov/pubmed/?term=18701580%5Bpmid%5D)
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1. [Brat DJ et al: Newly codified glial neoplasms of the 2007 WHO Classification of Tumours of the Central Nervous System: angiocentric glioma, pilomyxoid astrocytoma and pituicytoma. Brain Pathol. 17(3):319-24, 2007](http://www.ncbi.nlm.nih.gov/pubmed/?term=17598825%5Bpmid%5D)
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1. [Ceppa EP et al: The pilomyxoid astrocytoma and its relationship to pilocytic astrocytoma: report of a case and a critical review of the entity. J Neurooncol. 81(2):191-6, 2007](http://www.ncbi.nlm.nih.gov/pubmed/?term=16850101%5Bpmid%5D)
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1. [Morales H et al: Magnetic resonance imaging and spectroscopy of pilomyxoid astrocytomas: case reports and comparison with pilocytic astrocytomas. J Comput Assist Tomogr. 31(5):682-7, 2007](http://www.ncbi.nlm.nih.gov/pubmed/?term=17895777%5Bpmid%5D)
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1. [Komotar RJ et al: Astrocytoma with pilomyxoid features presenting in an adult. Neuropathology. 26(1):89-93, 2006](http://www.ncbi.nlm.nih.gov/pubmed/?term=16521485%5Bpmid%5D)
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1. [Melendez B et al: BCR gene disruption in a pilomyxoid astrocytoma. Neuropathology. 26(5):442-6, 2006](http://www.ncbi.nlm.nih.gov/pubmed/?term=17080723%5Bpmid%5D)
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1. [Cirak B et al: Proton magnetic resonance spectroscopic imaging in pediatric pilomyxoid astrocytoma. Childs Nerv Syst. 21(5):404-9, 2005](http://www.ncbi.nlm.nih.gov/pubmed/?term=15372294%5Bpmid%5D)
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1. [Komotar RJ et al: Pilomyxoid astrocytoma of the spinal cord: report of three cases. Neurosurgery. 56(1):191, 2005](http://www.ncbi.nlm.nih.gov/pubmed/?term=15617606%5Bpmid%5D)
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1. [Chikai K et al: Clinico-pathological features of pilomyxoid astrocytoma of the optic pathway. Acta Neuropathol (Berl). 108(2):109-14, 2004](http://www.ncbi.nlm.nih.gov/pubmed/?term=15168135%5Bpmid%5D)
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1. [Darwish B et al: Juvenile pilocytic astrocytoma 'pilomyxoid variant' with spinal metastases. J Clin Neurosci. 11(6):640-2, 2004](http://www.ncbi.nlm.nih.gov/pubmed/?term=15261239%5Bpmid%5D)
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1. [Komotar RJ et al: Pilomyxoid astrocytoma: a review. MedGenMed. 6(4):42, 2004](http://www.ncbi.nlm.nih.gov/pubmed/?term=15775869%5Bpmid%5D)
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1. [Arslanoglu A et al: MR imaging characteristics of pilomyxoid astrocytomas. AJNR Am J Neuroradiol. 24(9):1906-8, 2003](http://www.ncbi.nlm.nih.gov/pubmed/?term=14561626%5Bpmid%5D)
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1. [Burger PC et al: Pathology of diencephalic astrocytomas. Pediatr Neurosurg. 32(4):214-9, 2000](http://www.ncbi.nlm.nih.gov/pubmed/?term=10940774%5Bpmid%5D)
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1. [Tihan T et al: Pediatric astrocytomas with monomorphous pilomyxoid features and a less favorable outcome. J Neuropathol Exp Neurol. 58(10):1061-8, 1999](http://www.ncbi.nlm.nih.gov/pubmed/?term=10515229%5Bpmid%5D)
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## Images
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### Selected Images
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*Coronal graphic depicts a pilomyxoid astrocytoma (PMA). Note the large, bulky, H-shaped mass <img src='img/arrows/BS.png'/> centered in the hypothalamic/chiasmatic region and extending into both temporal lobes. The tumor is relatively well circumscribed and shows little/no edema. Glistening myxoid matrix is typical. Hemorrhage <img src='img/arrows/BO.png'/> occurs in ~ 20% of PMAs but is unusual in pilocytic astrocytoma (PA).*
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*Coronal graphic depicts a pilomyxoid astrocytoma (PMA). Note the large, bulky, H-shaped mass <img src='img/arrows/BS.png'/> centered in the hypothalamic/chiasmatic region and extending into both temporal lobes. The tumor is relatively well circumscribed and shows little/no edema. Glistening myxoid matrix is typical. Hemorrhage <img src='img/arrows/BO.png'/> occurs in ~ 20% of PMAs but is unusual in pilocytic astrocytoma (PA).*
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*Coronal T1 C+ MR in a 20-month-old with a PMA shows a large, heterogeneously enhancing hypothalamic mass <img src='img/arrows/CS.png'/>.*
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*Sagittal T2 MR in a 7-month-old with a PMA shows a large mass <img src='img/arrows/CS.png'/> centered in the hypothalamus and optic chiasm. Note the pituitary <img src='img/arrows/CO.png'/> pressed down along the floor of the sella. The large size of the tumor and the very young age of the patient are typical of a PMA.*
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*Axial ADC MR in the same patient shows almost universal increased signal in the tumor <img src='img/arrows/CS.png'/> compared to brain parenchyma, which is typical for low-grade astrocytic tumors, such as PMAs.*
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*Sagittal T1 C+ MR in a 2-year-old shows an avidly enhancing hypothalamic tumor <img src='img/arrows/CS.png'/>. This is a typical appearance for PMA.*
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*Axial SWI in the same patient shows multifocal areas of signal loss <img src='img/arrows/CS.png'/>, consistent with intratumoral microhemorrhage. Microhemorrhage is more common in PMAs compared to PAs. For this reason, it is helpful diagnostically to include SWI in evaluation of hypothalamic tumors.*
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*Sagittal T1 C+ MR in a 23-month-old demonstrates a homogeneously enhancing midbrain lesion <img src='img/arrows/CS.png'/>. Pathology revealed a PMA. Regardless of location, PMAs should be considered for any likely low-grade glioma in a very young child.*
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*Coronal T1 C+ MR in a 2-year-old with a uniformly enhancing mass <img src='img/arrows/CS.png'/> centered in the right cerebellar hemisphere is shown. Note the associated hydrocephalus <img src='img/arrows/CO.png'/>. While the cerebellum is the most common location for PAs, it is an uncommon location for PMAs.*
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*Axial T1 C+ MR in 9-year-old shows a rim-enhancing mass <img src='img/arrows/CS.png'/> with lack of adjacent edema. Enhancement patterns of PMAs vary greatly from solid homogeneous enhancement to peripheral enhancement, as seen here. Some degree of enhancement is almost universally present.*
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*Sagittal T1 C+ MR in a 3-year-old with an avidly enhancing intramedullary tumor <img src='img/arrows/CS.png'/>, found to be a PMA on pathology, is shown. While uncommon, PMAs have been reported to occur in the spine.*
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### Additional Images
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*Sagittal T2 MR in the same patient shows a large, lobulated tumor centered in the hypothalamus with exophytic extension of the tumor into the 3rd ventricle <img src='img/arrows/CS.png'/> and prepontine cistern <img src='img/arrows/CO.png'/>. A suprasellar location is the most common location for a PMA.*
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*Axial ADC map in the same patient shows hyperintense signal within the solid components of the tumor <img src='img/arrows/CS.png'/>, which is characteristic of hypothalamic gliomas. There is significant overlap in imaging features of PAs and PMAs.*
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*Sagittal T1 C+ MR in a 9-month-old with macrocephaly shows a large, centrally necrotic mass centered within the hypothalamus with extension into the sella <img src='img/arrows/CS.png'/> and 3rd ventricle.*
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*Axial T2* GRE MR in the same patient shows small foci of signal loss <img src='img/arrows/CS.png'/> centrally within the lesion, suggesting areas of microhemorrhage. Approximately 20% of PMAs show hemorrhage, which is rare in PAs. Whenever hemorrhage is identified in a hypothalamic glioma, a PMA should be suggested.*
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*Sagittal T2 MR in a 23-month-old with a PMA shows a homogeneously hyperintense lesion <img src='img/arrows/CS.png'/> centered in the midbrain. A PMA can occur anywhere, including the brainstem.*
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*Axial T2 MR in a 9-year-old shows a markedly hyperintense mass <img src='img/arrows/CS.png'/> centered in the right basal ganglia, causing obstruction at the foramina of Monro with obstructive hydrocephalus. Pathology revealed a PMA.*
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*Sagittal T1 C+ MR in a 9-year-old shows an enhancing mass projecting into the 3rd ventricle from the thalamus. PMA was diagnosed on biopsy.*
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*Anteroposterior MRA in the same patient shows encasement of the right anterior cerebral artery <img src='img/arrows/BS.png'/> and elevation of the middle cerebral artery <img src='img/arrows/BO.png'/> compared to the normal left side. No neovascularity was seen. A PMA was found at surgery.*
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*Coronal T1 C+ MR in a 3-year-old shows a large, inhomogeneously enhancing, suprasellar mass encasing the carotid bifurcation <img src='img/arrows/CC.png'/>.*
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*Sagittal T2 MR shows a large, hyperintense hypothalamic/optic chiasm mass <img src='img/arrows/CS.png'/>. This could be either a pilomyxoid or PA on the basis of imaging findings. A PMA was found at surgery.*
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*Coronal T2 MR in an infant with a large head shows markedly enlarged lateral ventricles and a lobulated, hyperintense suprasellar mass.*
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*Axial FLAIR MR in the same patient shows the large mass <img src='img/arrows/CS.png'/> completely fills the suprasellar cistern, elevating and encasing both middle cerebral arteries <img src='img/arrows/CO.png'/>. The mass is mildly hyperintense relative to cortex.*
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*Axial T1 C+ SPGR MR in the same patient shows the mass <img src='img/arrows/CS.png'/> enhances intensely and quite uniformly. The H-shaped configuration centered in the suprasellar cistern is classic for PMAs, which was confirmed at surgery. (Courtesy M. Thurnher, MD.)*
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*Axial FLAIR MR in a 3-year-old shows a large, H-shaped suprasellar mass with extension into the basal ganglia and both medial temporal lobes. The tumor is quite well delineated despite its size and shows no evidence for surrounding edema.*
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*Axial T1 C+ MR in the same patient shows intense, uniform enhancement.*
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*High-power mucin stain shows the mucinous matrix (blue) with embedded glial nuclei. MIB1 was elevated. Final diagnosis was a PMA (WHO grade II). (Courtesy R. Hewlett, MD.)*
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*Micropathology biopsied from the same patient shows neoplastic, bipolar, "pilocytic" cells. No Rosenthal fibers are seen.*
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*Axial T2 MR in a 20-month-old shows a huge, bulky suprasellar and medial temporal lobe mass. Scattered foci of T2 shortening within the mass <img src='img/arrows/BO.png'/> may represent hemorrhage (no T2* imaging was performed.)*
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*Axial T1 C+ MR in the same patient shows mixed solid and rim enhancement. Biopsy disclosed elongated "piloid" cells in a mucin-rich matrix, consistent with a PMA. (Courtesy R. Hewlett, MD.)*
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