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Differential Diagnosis of Brainstem Lesions on MRI

Best Reference Article

The most targeted published review is:

Renard D, Guillamo JS, Ion I, Thouvenot E. "Brainstem lesions: MRI review of standard morphological sequences." Acta Neurologica Belgica. 2022 Jun. PMID: 35428930 DOI: 10.1007/s13760-022-01943-y

This review specifically addresses MRI signal characteristics across all major brainstem disorders, covering: exact lesion localization within the brainstem, associated extra-brainstem abnormalities, signal behavior on T1/T2/FLAIR/DWI/contrast sequences, temporal evolution, and how clinical context narrows the differential. It is the most comprehensive dedicated review available in the recent literature.

Framework for MRI Differential Diagnosis

Identifying the cause of a brainstem lesion requires integrating six factors (per Renard et al. 2022):

Exact location within the brainstem (midbrain / pons / medulla; ventral / dorsal; tegmentum / base)
Signal on each sequence (T1, T2/FLAIR, DWI/ADC, T2*/SWI, post-Gd T1)
Associated lesions outside the brainstem
Enhancement pattern
Temporal evolution (acute vs. subacute vs. chronic)
Clinical context (age, tempo of onset, systemic disease, immune status)

Categories and Key Distinguishing MRI Features

1. Vascular

Condition	MRI Hallmarks
Ischemic infarct (basilar territory)	DWI bright / ADC dark (acute); T2/FLAIR hyperintense; distribution matches penetrating branches; no enhancement acutely
Lateral medullary (Wallenberg) infarct	DWI restriction in the dorsolateral medulla; ipsilateral Horner + crossed sensory loss clinically
Basilar artery occlusion	Bilateral pons DWI restriction; T2 hyperintensity; MRA shows occlusion
Brainstem cavernoma	"Popcorn" T2 heterogeneity; blooming on T2*/SWI (hemosiderin ring); no enhancement unless recently bled
Brainstem hemorrhage	Hyperdense on CT; T1 bright (subacute) / T2 dark (acute/chronic); SWI blooms

Bradley and Daroff's Neurology in Clinical Practice - brainstem penetrating branch lesions produce contralateral weakness + ipsilateral cranial nerve palsy (crossed syndromes)

2. Neoplastic

Condition	MRI Hallmarks
Diffuse intrinsic pontine glioma (DIPG)	Children; diffusely expanded pons; T2 hyperintense, T1 hypointense; minimal or patchy enhancement; involves >50-60% of pons cross-section
Focal brainstem glioma (pilocytic astrocytoma)	Children/young adults; exophytic or focal; T2 hyperintense; intense contrast enhancement; favorable prognosis
Metastasis	Adults; well-circumscribed; ring or nodular enhancement; surrounded by vasogenic edema; multiple lesions common
Lymphoma (primary CNS)	Periventricular or deep structures; homogeneous enhancement; DWI restriction; responds to steroids
Haemangioblastoma	Mural nodule + cyst; intense nodular enhancement; associated with VHL

Grainger & Allison's Diagnostic Radiology - brainstem astrocytoma: diffuse low T1, high T2 signal; sagittal C+ T1 shows variable enhancement patterns

3. Demyelinating / Inflammatory

Condition	MRI Hallmarks
Multiple sclerosis (MS)	Ovoid T2 lesions in tegmentum/floor of 4th ventricle; juxtacortical and periventricular lesions elsewhere; Dawson fingers on sagittal FLAIR; incomplete ring enhancement
Neuromyelitis optica spectrum disorder (NMOSD)	Dorsal brainstem lesions adjacent to 4th ventricle (area postrema); longitudinally extensive spinal cord lesion (>3 segments); "bright spotty lesions" on axial T2 cord; AQP4-Ab positive
ADEM	Post-infectious/post-vaccination; multifocal T2 hyperintense lesions in white matter, brainstem, basal ganglia/thalamus; typically monophasic; may or may not enhance
CLIPPERS	Pathognomonic pattern: symmetric punctate and curvilinear gadolinium enhancement "peppering" the pons and extending to medulla/cerebellum/brachium pontis; T2 signal not greatly exceeding enhancement area; dramatic steroid response
Bickerstaff brainstem encephalitis	Post-infectious; ophthalmoplegia + ataxia + drowsiness; MRI may show T2 brainstem swelling or be normal; anti-GQ1b antibodies

Bradley and Daroff's: CLIPPERS - "symmetric curvilinear gadolinium enhancement peppering the pons" with near-complete resolution after steroids - p. 733
Plum and Posner's: CLIPPERS was previously misdiagnosed as "sarcoidosis" or "demyelination" - p. 333

4. Infectious

Condition	MRI Hallmarks
Brainstem abscess	Ring-enhancing lesion; DWI restriction centrally (pus); perilesional edema; T1 dark / T2 bright core
Listeria brainstem encephalitis (rhombencephalitis)	Pons/medulla predominant; T2 hyperintensity; immunocompromised or elderly; punctate enhancement
Viral encephalitis (HSV, enterovirus)	T2/FLAIR hyperintensity; DWI often positive; may enhance; CSF PCR diagnostic
Brainstem cryptococcoma	Ring-enhancing mass; immunocompromised; India ink + CSF cryptococcal antigen
Tuberculoma	Homogeneous or ring enhancement; may have central T2 dark "target sign" on T2 (caseous); basal meningeal enhancement

5. Metabolic / Toxic

Condition	MRI Hallmarks
Osmotic demyelination (Central Pontine Myelinolysis/ODS)	Trident or bat-wing T2 hyperintensity in central pons; spares peripheral fibers; follows rapid hyponatremia correction; DWI may be bright acutely; no enhancement
Wernicke encephalopathy	Symmetric T2/FLAIR hyperintensity in periaqueductal gray, mamillary bodies, dorsomedial thalami; DWI + in acute cases
Leigh syndrome (mitochondrial)	Symmetric T2 hyperintensity in brainstem tegmentum + basal ganglia + thalami; pediatric

6. Autoimmune / Systemic Inflammatory

Condition	MRI Hallmarks
Neurosarcoidosis	Leptomeningeal + perivascular enhancement; cranial nerve enhancement; parenchymal T2 lesions; periventricular pattern; responds partially to steroids
Neuro-Behcet disease	Pontine tegmentum/midbrain junction T2 lesion ("mesodiencephalic junction" predilection); edematous; sub-acute onset in young males; associated uveitis/oral ulcers
CNS vasculitis	Multiple small T2 lesions; DWI infarcts in multiple territories; leptomeningeal enhancement on high-resolution vessel wall MRI

7. Structural / Compressive

Condition	MRI Hallmarks
Epidermoid cyst (CPA)	DWI bright; T2 bright; no enhancement; fills cisterns
Chordoma	Destructive clivus mass; T2 very bright; invades brainstem; lobulated; moderate enhancement
Extrinsic compression (meningioma, neurinoma)	Extra-axial; dural tail; homogeneous enhancement; brainstem displaced

Practical Approach: Reading the MRI

Acute onset + DWI restriction  → Ischemic infarct (most likely)
Blooming on SWI               → Cavernoma or hemorrhage
Ring enhancement + DWI core   → Abscess
Nodular/ring Gd + edema       → Metastasis or primary tumor
Peppering pontine enhancement → CLIPPERS
Periventricular + ovoid T2    → MS
Area postrema lesion          → NMOSD
Post-infection + ophthalmoplegia → Bickerstaff / ADEM
Central pons bat-wing T2      → Osmotic demyelination
Periaqueductal + mamillary T2 → Wernicke

Key Textbook Sources Used

Bradley and Daroff's Neurology in Clinical Practice - Brainstem syndromes, CLIPPERS, ADEM, neurosarcoidosis
Plum and Posner's Diagnosis and Treatment of Stupor and Coma - Infratentorial tumors, CLIPPERS, Bickerstaff encephalitis, central pontine myelinolysis
Grainger & Allison's Diagnostic Radiology - MRI signal characteristics of astrocytoma, NMOSD, ADEM variants, Bickerstaff encephalitis
Adams and Victor's Principles of Neurology - Central pontine myelinolysis

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