Masses & pseudomasses

Infectious/inflammatory processes versus metabolic disorders

Focal reduction in aqueduct size, congenital or benign acquired

Funnel-shaped aqueduct with “ballooned” lateral & 3rd ventricles & foramen of Monro proximal to obstruction

Normal 4th ventricle & foramina distal

All patients with suspected AS should be scrutinized for an obstructing mass!

↑ T2 signal mass; ± enhancement

Expands tectum, obstructs aqueduct

Indolent, most only need CSF diversion

Multifocal punctate hemorrhages at corticomedullary junction, corpus callosum, deep gray matter (GM) & upper brainstem (dorsolateral midbrain & pons)

Multifocal hypointense T2*/GRE foci related to blood product susceptibility

Cisterns > parenchyma > ventricles

Basal cistern cysts may be racemose (grape-like), causing an aqueduct lesion

Multiple T2 hyperintensities in periventricular white matter (WM) & callososeptal interface; 10% infratentorial

Internuclear ophthalmoplegia (INO): Characteristic clinical finding related to brainstem lesion involving medial longitudinal fasciculus, present within periaqueductal region

Benign fluid-filled structures, accompany penetrating arteries

PVS usually 5 mm or less; may expand

Most common location for expanded “giant” PVS is midbrain; may cause hydrocephalus

Single or multiple well-delineated cysts isointense with CSF; no enhancement

Nonenhancing T2 hyperintense mass; supratentorial 2/3, infratentorial 1/3

50% of brainstem “gliomas” are low grade astrocytoma

Usually no enhancement, if C+ worry about malignant progression

Location dependent on etiology

Diffuse brain parenchymal inflammation caused by a variety of pathogens, most commonly viruses

Abnormal T2 hyperintensity of GM ± WM or deep gray nuclei

Epstein-Barr virus: Symmetric BG, thalami, cortex, or brainstem

Varicella-zoster virus: Brainstem/cortical GM, cranial nerves

Japanese encephalitis: Bilateral thalami, brainstem, cerebellum, spinal cord, cerebral cortex

Listeria rhombencephalitis: Brainstem & cerebellum

West Nile virus: Brainstem, substantia nigra, BG, thalami, anterior horn (cord), cerebellum

Enteroviral encephalomyelitis: Brainstem, spinal cord, & cerebellum

Associated with significant trauma

May occur within cerebral aqueduct

Symmetric T2 hyperintensity or mixed signal in putamen, globus pallidus (GP), caudate, & thalami

Characteristic “face of the giant panda” sign at midbrain

May involve brainstem; typically multiple lesions

Curable neurologic disease caused by thiamine deficiency

Triad of neuro-ophthalmologic manifestations, ataxia, & global confusion

Symmetric increased T2 signal surrounding aqueduct & 3rd ventricle, floor of 4th ventricle & medial thalami

May affect only periaqueductal grey matter

Multisystem vasculitis of unknown origin, CNS involvement 5-10%

Classic triad of oral & genital ulcerations with uveitis

T2 hyperintense lesions in brainstem, BG /or deep WM