Asymmetric Lateral Ventricles

Bronwyn E. Hamilton, MD

DIFFERENTIAL DIAGNOSIS

Common

Normal Variant
Extrinsic Mass Effect
Encephalomalacia, General
Intraventricular Hemorrhage
Herniation Syndromes, Intracranial
Surgical Defects
Obstructive Hydrocephalus
Choroid Plexus Cyst

Less Common

Ventriculitis
CSF Shunts and Complications
Meningioma
Choroid Plexus Papilloma
Neurocysticercosis

Rare but Important

Intraventricular Synechiae/Adhesions
Choroid Plexus Carcinoma
Ependymal Cyst
Dyke-Davidoff-Masson
Hemimegalencephaly

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Asymmetric lateral ventricles are most commonly seen as a normal variant

Helpful Clues for Common Diagnoses

Normal Variant
- Asymmetric lateral ventricles seen in 5-10% of normal population
- Asymmetry mild-moderate, left > right
- Septum may be displaced across the midline
- No associated mass effect, herniation, or parenchymal atrophy
- Must exclude underlying mass or obstructing lesion
Extrinsic Mass Effect
- Etiologies include mass, hemorrhage, infarct, infection
- Mass can cause ventricular deformity, subfalcine herniation
Encephalomalacia, General
- Parenchymal loss results in compensatory ventricular enlargement
- Common etiologies include chronic infarct, trauma, surgery
Intraventricular Hemorrhage
- Involved ventricle may dilate early from mass effect
- Chronic dilation may be due to scarring from adhesions
- Etiologies include trauma, AVM, basal ganglia hemorrhage
Herniation Syndromes, Intracranial
- Subfalcine herniation: Cingulate gyrus herniates under falx
  - Ipsilateral lateral ventricle compressed
  - Foramen of Monro obstructs, causes contralateral lateral ventricle enlargement
- Unilateral descending transtentorial herniation (uncal): Herniation of medial temporal lobe inferiorly
  - Contralateral temporal horn becomes entrapped & enlarges
- Entrapped ventricle: Typically temporal horn, by extrinsic mass effect
Surgical Defects
- Look for calvarial defect or “tract”
- Typically related to resection of mass
- Ventricle enlarged unilateral to defect
Obstructive Hydrocephalus
- Typically acquired & bilateral
- May be unilateral if shunt complication or obstructing tumor is cause
- Rare: Colloid cyst may obstruct unilateral foramen of Monro & cause unilateral ventriculomegaly
Choroid Plexus Cyst
- Nonneoplastic, noninflammatory cyst of the choroid plexus
- Common incidental finding in older patients (40% prevalence)
- Typically bilateral, may be unilateral & enlarge lateral ventricle

Helpful Clues for Less Common Diagnoses

Ventriculitis
- Ventriculomegaly with debris level, enhancing ependyma
- May affect lateral ventricles asymmetrically, particularly if related to shunt placement or abscess rupture
CSF Shunts and Complications
- Common complications include shunt obstruction or breakage, infection, overdrainage
- Asymmetric ventricles may result from overdrainage or underdrainage of an “isolated” ventricle
Meningioma
- Intraventricular meningioma rare, typically left lateral ventricle
- Associated with choroid plexus
- Smooth enhancing intraventricular mass
Choroid Plexus Papilloma
- Enhancing, lobulated intraventricular mass in a child
- 50% in lateral ventricle atrium, left > right
- May obstruct CSF flow or overproduce CSF
- May have CSF spread of tumor
Neurocysticercosis
- Intraventricular disease uncommon
- Rarely may obstruct unilateral foramen of Monro & cause asymmetric lateral ventricle
- Cyst with “dot” representing scolex characteristic
- T1 & FLAIR best show intraventricular cysts

Helpful Clues for Rare Diagnoses

Intraventricular Synechiae/Adhesions
- May be congenital or acquired (prior bleed, infection, tumor)
- Look for enhancing septae, intraventricular cysts within ventricle
Choroid Plexus Carcinoma
- Enhancing intraventricular mass & ependymal invasion in young child
- CSF seeding common
Ependymal Cyst
- Nonenhancing thin-walled cyst with CSF density/intensity
- Lateral ventricle most common location
Dyke-Davidoff-Masson
- Antenatal unilateral hemispheric infarction causes cerebral hemiatrophy
- Ipsilateral calvarial thickening & hyperpneumatized frontal sinuses, temporal bones
- Dilated ventricle from volume loss is ipsilateral to small hemisphere
Hemimegalencephaly
- Unilateral hemispheric enlargement
- Dilated, usually dysmorphic ventricle ipsilateral to enlarged hemisphere
- Ipsilateral extracalvarial soft tissues may be larger

Other Essential Information

High resolution “MR cisternography”: CISS, balanced FFE, FIESTA
- May detect small septations or arachnoid membranes causing obstruction
Cine CSF flow study may help detect physiologic flow obstruction from arachnoid webs or membranes
- May assess adequacy of drainage procedures