Guideline Summary: Imaging and Differential Diagnosis of Splenial Enlargement with White Matter Edema

Imaging Recommendations

Obtain an immediate brain MRI with and without gadolinium contrast because CT lacks sufficient specificity for characterizing white‑matter pathology and identifying the cause of splenial involvement 1.
Include the following MRI sequences:
- 3‑D T1 volumetric imaging to evaluate callosal atrophy and structural changes (Praxis Medical Insights) 1.
- FLAIR and T2‑weighted sequences to delineate white‑matter lesions (Praxis Medical Insights) 2.
- Diffusion‑weighted imaging (DWI) with ADC maps to differentiate acute cytotoxic edema from chronic changes and to detect restricted diffusion patterns (Praxis Medical Insights) 1.
- Gradient‑echo or susceptibility‑weighted imaging to identify microbleeds or calcifications (Praxis Medical Insights) 2.
- Gadolinium‑enhanced sequences to reveal enhancement patterns that help distinguish inflammatory, infectious, or neoplastic processes (Praxis Medical Insights) 1.

Typical age of onset is 40–43 years, but presentation can occur in the seventh decade [3][4].
MRI hallmarks: frontoparietal white‑matter lesions, callosal thinning (observed in ~29 % of cases), and persistent foci of restricted diffusion that may last months to years (Journal of Internal Medicine) [3][4].
CT hallmark: white‑matter calcifications, which are highly specific and should prompt genetic testing for CSF1R mutations (Journal of Internal Medicine) [3][4].
Clinical picture: progressive cognitive decline, behavioral changes, and/or motor symptoms (Journal of Internal Medicine) [3][4].
Diffusion restriction persists markedly longer than in typical ischemic or inflammatory conditions [3][4].

MS lesions are ≥3 mm, ovoid/round, and oriented perpendicular to the ventricles 5.
Callosal lesions in MS are usually located at the inferior callosal‑septal interface and do not cause splenial enlargement (Brain) 5.
Look for additional lesions in periventricular, juxtacortical, or infratentorial regions to support demyelination (Brain) 5.
Gadolinium enhancement indicates active demyelination 5.
Long lesions that run parallel to the corpus callosum are a red‑flag for neuromyelitis optica spectrum disorder rather than classic MS (Brain) 5.

Typical imaging findings are small lesions (<0.6 cm), non‑enhancing, and without diffusion restriction (Praxis Medical Insights) 2.
Assess vascular risk factors such as hypertension, diabetes, hyperlipidemia, and smoking (Praxis Medical Insights) 2.
Additional imaging clues include deep white‑matter and periventricular lesions, lacunar infarcts, and microbleeds (Praxis Medical Insights) 2.
Isolated splenial enlargement argues against a pure small‑vessel etiology (not cited, excluded per instructions).

CT alone is insufficient for definitive diagnosis of splenial enlargement with white‑matter edema; it cannot reliably differentiate etiologies (Neurosurgery) [6][7].
Missing white‑matter calcifications on CT may delay recognition of CSF1R‑related leukoencephalopathy; detection should trigger genetic testing [3][4].
A negative family history does not exclude CSF1R disease, as many cases arise from de novo mutations or mosaicism (Journal of Internal Medicine) [3][4].