Add comprehensive articles on Vascular Dementia and Wallerian Degeneration

- Created a detailed article for Vascular Dementia covering key facts, terminology, imaging findings, differential diagnoses, pathology, clinical issues, and diagnostic checklist.
- Developed an extensive article on Wallerian Degeneration including key facts, terminology, imaging features, differential diagnoses, pathology, clinical issues, and diagnostic checklist.

docs_md/articles/cyst-with-nodule_6cb71737-f574-4121-a8fb-02eeada9f9f7.md

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+---
+title: "Cyst With Nodule"
+docid: "6cb71737-f574-4121-a8fb-02eeada9f9f7"
+breadcrumbs:
+  - "Brain"
+  - "Differential Diagnosis"
+  - "Brain Parenchyma, General"
+  - "Generic Imaging Patterns"
+  - "Cyst With Nodule"
+---
+# ESSENTIAL INFORMATION
+
+- ## Key Differential Diagnosis Issues
+  
+  
+    - Cystic lesions with solid nodular components can be divided into 2 categories
+          - Lesions that typically demonstrate cyst with nodule morphology
+                  - Neurocysticercosis (NCC), pilocytic astrocytoma, ganglioglioma, hemangioblastoma, pleomorphic xanthoastrocytoma (PXA), desmoplastic infantile ganglioglioma (DIG), intraparenchymal schwannoma
+          - Lesions that may demonstrate cyst with nodule morphology
+                  - Metastases, glioblastoma (GBM), abscess, toxoplasmosis, parasites, dysplastic neuroepithelial tumor (DNET), thrombosed arteriovenous malformation (AVM), supratentorial ependymoma
+    - Although metastases, abscesses, & GBMs do not classically present as "cysts with nodules," they are included because of their overall prevalence
+          - Statistically, atypical form of these common diseases may be more likely than some of other "classic" cysts with nodule lesions
+- ## Helpful Clues for Common Diagnoses
+  
+  
+    - **Neurocysticercosis**
+          - Intracranial parasitic infection caused by pork tapeworm *Taenia solium*
+          - Cyst with "dot" inside representing scolex
+          - Imaging appearance varies with stage; increased enhancement & edema when organism dies (inflammatory host response)
+          - Location: Convexity subarachnoid space > > cisterns > parenchyma > ventricles
+          - Lesions may be at different stages in same patient
+    - **Pilocytic Astrocytoma**
+          - Cerebellar cystic mass with mural nodule in child; rarely supratentorial
+          - T1 C+ MR: Nodule shows intense but heterogeneous enhancement
+                  - Cyst wall may show enhancement
+          - T1 & T2 MR: Cyst content iso- to hyperintense to CSF
+          - Most common brain tumor in children
+    - **Ganglioglioma**
+          - Cortically based, slow-growing, enhancing mass in older child or young adult
+          - Circumscribed cyst with mural nodule most common
+          - May be solid and appear well circumscribed
+          - Often expands cortex; calcification common
+          - Most common tumor to cause temporal lobe epilepsy
+          - Cortical dysplasia is commonly associated
+    - **Hemangioblastoma**
+          - Vascular neoplasm of uncertain etiology
+          - Parenchymal posterior fossa cyst with nodule mass in adult
+          - T1 C+ MR: Nodule abuts pial surface & shows intense, homogeneous enhancement
+          - Prominent flow voids may be seen
+          - Multiple in von Hippel-Lindau syndrome (VHL) (25-40% of hemangioblastomas)
+- ## Helpful Clues for Less Common Diagnoses
+  
+  
+    - **Metastases, Parenchymal**
+          - Discrete, gray-white interface mass(es) with adjacent vasogenic edema
+          - Multiplicity, history of primary malignancy helpful if present
+          - Solitary metastasis may mimic GBM
+          - Often known history of primary neoplasm
+    - **Glioblastoma, IDH-Wildtype**
+          - Malignant white matter mass with central necrosis
+          - Predilection to spread across midline along corpus callosum; "butterfly glioma"
+          - T1 C+ MR: Thick, irregular, nodular, enhancing margins
+          - T2/FLAIR MR: Surrounding hyperintensity & mass effect reflect edema + infiltrative tumor
+    - **Pleomorphic Xanthoastrocytoma**
+          - Cortically based cyst + nodule ± involvement of adjacent meninges
+          - T1 C+ MR
+                  - Enhancing nodule
+                  - Thickening, enhancement of adjacent meninges
+                  - 70% have dural tail
+          - Temporal lobe predominance; young adult
+          - Maybe associated with cortical dysplasia
+    - **Abscess**
+          - T2 MR: Hypointense rim with surrounding edema classic
+          - T1 C+ MR: Enhancing capsule thinnest at ventricular side
+          - DWI MR: Cystic component bright (diffusion restriction)
+          - SWI MR: Dual rim sign (hypointense outside, hyperintense inside )
+    - **Opportunistic Infection, AIDS, Toxoplasmosis**
+          - Caused by parasite *Toxoplasma gondii*
+          - Toxoplasmosis: Ring-enhancing lesion containing eccentric nodule = eccentric target sign specific but not sensitive
+          - Location: Basal ganglia > hemispheres
+          - Clinical: Immunocompromised patient
+    - **Parasites, Miscellaneous**
+          - Multiple enhancing lesions typical
+          - May mimic brain tumor
+          - Travel history critical
+    - **Dysplastic Neuroepithelial Tumor**
+          - Bubbly, wedge-shaped, cortically based mass "points" toward lateral ventricle
+          - T2 MR: Very hyperintense; nodular, septate; no surrounding edema
+          - FLAIR MR: Hyperintense ring sign
+                  - Thin rim of well-defined peritumoral hyperintensity separating it from surrounding normal brain
+          - T1 C+ MR: No to minimal enhancement; may be nodular
+          - Temporal lobe predominance
+- ## Helpful Clues for Rare Diagnoses
+  
+  
+    - **Desmoplastic Infantile Ganglioglioma**
+          - Supratentorial cystic/nodular mass with dominance of cyst
+          - Cortically based nodule with intense enhancement & dural tail
+          - May be massive
+          - Peak age: 3-6 months
+    - **Schwannoma, Intraparenchymal**
+          - Only 1-2% of schwannomas are parenchymal
+          - Cyst with strongly enhancing nodule
+    - **Arteriovenous Malformation**
+          - When hemorrhagic with partial or complete thrombosis, may present as cyst with nodule
+          - Blood breakdown products of various ages; fluid-fluid levels
+    - **Ependymoma, Supratentorial**
+          - 40% of supratentorial ependymomas are extraventricular
+          - Large, complex, mixed solid/cystic mass
+          - Calcification, intratumoral hemorrhage common
+          - Moderate but inhomogeneous enhancement
+    - **Meningioma (Cystic)**
+          - Meningioma with intraparenchymal cyst may mimic cyst + nodule mass
+    - **Rosette-Forming Glioneuronal Tumor**
+          - Rare, slowly growing benign tumor of young adults
+          - 4th ventricle most common site > cerebellum
+          - Mixed solid-cystic appearance, variable Ca⁺⁺, hemorrhage
+          - May show cyst with nodule configuration
+    - **Papillary Glioneuronal Tumor**
+          - Temporal lobe predilection
+          - Parenchymal mass with solid, cystic, or cyst/mural nodule architecture
+                  - May show calcification
+          - Imaging may be indistinguishable from ganglioglioma
+- ## Alternative Differential Approaches
+  
+  
+    - By location
+          - Posterior fossa: Pilocytic astrocytoma, hemangioblastoma, metastasis, Rosette-forming glioneuronal tumor
+          - Temporal lobe: Ganglioglioma, PXA, DNET, papillary glioneuronal tumor
+          - Gray-white junction: Metastases, abscess
+          - Hemispheric: NCC, metastases, GBM, infections, DIG, AVM, supratentorial ependymoma
+    - Patient age
+          - Child & young adult: Pilocytic astrocytoma, ganglioglioma, PXA, DNET
+          - Adult: Hemangioblastoma, GBM, metastases
+          - Any age: NCC, abscess, other infections
+    - Multiple lesions
+          - Metastases (50-55%), NCC (50-70%), hemangioblastoma (VHL), abscesses (septic emboli), toxoplasmosis, parasites