What childhood cancer could present with labyrinthine enhancement on MRI with contrast and an otherwise normal study?

Leukemia as the Primary Consideration for Labyrinthine Enhancement with Otherwise Normal MRI

Acute lymphoblastic leukemia (ALL) is the childhood cancer most likely to present with isolated labyrinthine enhancement on MRI with contrast when the remainder of the study appears normal. This occurs due to leukemic infiltration of the inner ear structures, particularly affecting the membranous labyrinth and cochlea.

Why Leukemia Presents This Way

Leukemic cells have a propensity to infiltrate highly vascularized structures, and the labyrinth's rich blood supply makes it vulnerable to hematogenous spread. The enhancement pattern reflects:

• Direct leukemic infiltration of the membranous labyrinth, which appears as abnormal enhancement on post-contrast T1-weighted sequences
• Absence of mass effect or other CNS findings in early disease, making the MRI otherwise appear normal
• Bilateral involvement is common, though asymmetric presentation can occur

Clinical Context and Associated Findings

Children with leukemic labyrinthine involvement may present with:

• Hearing loss (sensorineural, often sudden onset)
• Vertigo or balance disturbances
• Tinnitus
• Facial nerve palsy in some cases

The diagnosis should be suspected particularly in children with:

• Known leukemia diagnosis (relapsed or refractory disease)
• Unexplained cytopenias on complete blood count
• Constitutional symptoms (fever, weight loss, fatigue)
• Bone pain or lymphadenopathy

Imaging Protocol Recommendations

When labyrinthine enhancement is identified, the workup should include:

• High-resolution T1-weighted post-contrast sequences through the temporal bones to confirm enhancement pattern
• T2-weighted sequences to assess for labyrinthine hemorrhage (T2 hypointensity would suggest this)
• Diffusion-weighted imaging may show restricted diffusion in leukemic infiltrates
• Complete brain and spine MRI with contrast to evaluate for leptomeningeal disease, which can coexist

Differential Considerations

While leukemia is the primary concern, other entities that can cause labyrinthine enhancement include:

• Labyrinthitis (infectious/inflammatory) - typically presents with acute vestibular symptoms and may show T2 hyperintensity
• Labyrinthine hemorrhage - shows T1 hyperintensity even without contrast
• Neuroblastoma with metastatic spread - though this typically shows additional findings such as bone involvement or soft tissue masses 1

Critical Next Steps

When isolated labyrinthine enhancement is identified:

1. Obtain complete blood count with differential immediately to evaluate for cytopenias or circulating blasts
2. Perform lumbar puncture with CSF cytology if leukemia is suspected, as CNS involvement requires modified treatment
3. Bone marrow aspiration and biopsy for definitive diagnosis if not previously performed
4. Audiology evaluation to document baseline hearing function

Common Pitfalls to Avoid

• Do not dismiss isolated labyrinthine enhancement as artifact or normal variant - it always requires explanation
• Do not assume infectious labyrinthitis without considering malignancy, especially if symptoms are subacute or constitutional symptoms are present
• Do not delay hematologic workup while pursuing additional imaging studies
• Do not overlook bilateral involvement even if asymmetric, as this strongly suggests systemic disease rather than focal infection

The key distinguishing feature is that leukemic infiltration produces enhancement on an otherwise normal MRI, whereas most other childhood CNS malignancies would show additional abnormalities such as mass lesions, parenchymal signal changes, or leptomeningeal disease 1.