Overview
- ACC refers to complete or partial absence of the corpus callosum, one of the most common fetal neurological diagnoses.
- Increasing use of fetal ultrasound and MRI has improved understanding of incidence, associated findings, and prognosis.
- Can be:
- Complete (entire corpus callosum absent).
- Partial (hypogenesis or dysgenesis): incomplete formation or abnormal structure of parts of the corpus callosum.
Embryological Background
- Corpus callosum formation involves multiple midline components.
- Traditionally thought that partial ACC involved failure of posterior corpus callosum (splenium); however, partial ACC may involve failure of any callosal region.
- Corpus callosum formed between weeks 12–20 gestation:
- Fully formed by about 20 weeks gestation.
- Diagnosis of partial ACC difficult before 20 weeks.
Diagnosis
Ultrasound Challenges:
- Fetal ultrasound detection challenging due to fetal movement.
- High false-positive rate (~20%) with ultrasound alone.
- Limited sensitivity to associated anomalies.
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