Pontine Lesion

Nancy J. Fischbein, MD

DIFFERENTIAL DIAGNOSIS

Common

Less Common

Rare but Important

Brainstem Encephalitis
Vasculitis
Multiple System Atrophy
Radiation Necrosis
Mitochondrial Disorder
Maple Syrup Urine Disease
Infiltrative Disorder
- Langerhans Cell Histiocytosis; Neurosarcoid; Whipple Disease

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Helpful Clues for Common Diagnoses

Arteriolosclerosis (Ischemic Rarefaction)
- Ischemic rarefaction of pons very common in older patients with ASVD risk factors
- Mild diffuse ↑ SI on T2WI without mass effect, enhancement, or ↓ diffusion
Cerebral Ischemia-Infarction, Acute
- Pontine infarct typically respects the midline & shows reduced diffusion
  - Consider CTA or MRA to assess vertebrobasilar circulation
Hypertensive Intracranial Hemorrhage
- Hypertensive hemorrhages usually central
- Acute pontine hemorrhage usually hypertensive, but may be due to cavernoma or AVM
- CTA or MR/MRA to look for AVM
Brainstem Tumor
- Massive expansion of pons, “engulfing” basilar artery, often nonenhancing
- Typically diffuse fibrillary astrocytoma
Vascular Lesion
- Capillary telangiectasia: Usually small, asymptomatic; “feathery” enhancement; signal loss on GRE; common in pons

Helpful Clues for Less Common Diagnoses

Demyelinating Disease (MS, ADEM)
- Often involvement of middle cerebellar peduncles; incomplete ring enhancement
- Additional lesions in corpus callosum, hemispheric white matter (WM), spinal cord, optic nerves
Malignant Neoplasm
- High grade tumor (GBM, PNET) often accompanied by edema, irregular enhancement, increased CBV
- Metastases to pons associated with edema, often other enhancing lesions of brain parenchyma, dura, bone
- Lymphoma usually homogeneously enhances, may show mildly diffusion
Pilocytic Astrocytoma
- Focal enhancing lesion without edema
Wallerian Degeneration
- Acute: Variable ↓ diffusion and ↑ SI on T2
- Chronic: Volume loss; variable T2 SI
Acute Hypertensive Encephalopathy, PRES
- Most commonly involves parietooccipital subcortical WM
- Infratentorial T2 hyperintensity often present in pons, cerebellum
- Best appreciated on FLAIR; usually no enhancement or DWI abnormality
Focal or Multifocal Infection
- Pyogenic abscess will typically reduce diffusion, whereas tuberculoma may not
- PML often causes multiple small dots of T2 hyperintensity in the brainstem
Osmotic Demyelination Syndrome
- Commonly involves central pons, spares corticospinal tracts, may show ↓ diffusion
Neurofibromatosis Type 1
- Common in dorsal pons, due to dysmyelination/myelin vacuolization
- No mass effect, enhancement