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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