Epidemiology

Etiology

Abnormal accumulation of cerebrospinal fluid (CSF) leading to ventricular enlargement and ↑ intracranial pressure (ICP).
Non-communicating (Obstructive)
- Caused by a structural blockage of CSF flow within the ventricular system.
- Leads to enlargement of ventricles proximal to the obstruction.
- Common causes:
  - Aqueductal stenosis (most common cause in newborns)
  - Tumors (e.g., colloid cyst of the 3rd ventricle, posterior fossa tumor)
  - Arnold-Chiari malformation
  - Dandy-Walker malformation: congenital malformation caused by failure of the fourth ventricle to close, which leads to persistence of Blake’s pouch (cyst in the 4th ventricle) and cerebellar vermis hypoplasia
    - Causes a variety of neurologic abnormalities (e.g., ataxic gait) and noncommunicating hydrocephalus
    - Associated with a variety of extracranial abnormalities (e.g., craniofacial abnormalities, cardiac defects, spina bifida)
Communicating
- Caused by ↓ CSF absorption by arachnoid granulations.
- All ventricles are symmetrically enlarged.
- Common causes:
  - Post-meningitis scarring
  - Subarachnoid hemorrhage (blood clogs granulations)
Normal Pressure Hydrocephalus (NPH)
- Chronic form of communicating hydrocephalus in the elderly.
- CSF pressure is episodically elevated but often normal on lumbar puncture.
- Pathophysiology: Impaired absorption at arachnoid granulations leads to ventricular expansion that stretches the corona radiata fibers.

Chiari malformation vs Dandy-Walker malformation

Feature Chiari Malformation Dandy-Walker Malformation
Pathophysiology Cerebellum herniates through foramen magnum due to small posterior fossa. Agenesis of cerebellar vermis allows 4th ventricle to enlarge into a cyst.
Posterior Fossa Small / Normal Enlarged
Key Abnormality Tonsillar (Type I) or vermis + tonsillar (Type II) herniation. Absent cerebellar vermis.
Hydrocephalus Common, due to CSF outflow obstruction. Very common, due to cystic 4^th ventricle.
Key Associations - Type I: Syringomyelia.
- Type II: Myelomeningocele. Hydrocephalus, Spina Bifida, Agenesis of corpus callosum.
Typical Presentation - Type I: Adult w/ headaches.
- Type II: Infant w/ brainstem dysfunction. Infant w/ macrocephaly.

Chiari畸形：过度拥挤的房间

请把后颅窝想象成一个小卧室，把小脑和脑干想象成里面的家具。

问题所在： 在Chiari畸形中，这个房间建得太小了，无法容纳所有它需要放置的家具。

后果： 为了把所有东西都塞进去，一部分家具（小脑扁桃体）被挤了出来，并从唯一的开口——门道（枕骨大孔）——伸了出去。

结果： 这些堵在门口的家具阻碍了交通（脑脊液流动），导致房间内压力积聚（脑积水），并影响到走廊的墙壁（脊髓空洞症）。

核心：Chiari是一个_拥挤_问题。

Dandy-Walker畸形：缺失的帐篷支柱

请把后颅窝想象成一个大帐篷，把小脑蚓部想象成它主要的中央支撑柱。

问题所在： 在Dandy-Walker畸形中，这根中央帐篷支柱缺失了（蚓部发育不全）。

后果： 没有了支柱的支撑，帐篷的顶部（第四脑室）无法正常成型。它会塌陷并被“雨水”（脑脊液）充满，形成一个巨大的、充满液体的囊肿。

结果： 这个不断膨胀的水囊肿将帐篷壁向外推（后颅窝扩大），并堵住了拉链出口（脑脊液流出道），将所有的水都困在里面，导致整个帐篷都肿胀起来（脑积水）。

核心：Dandy-Walker是一个_结构缺陷_问题。
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Pathophysiology

Clinical features

Diagnostics

Treatment

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