How many letters does the top answer for “a defect in brain development resulting in small or missing brain hemispheres” have?

The most common answer is anencephalia (12 letters).

Crossword clue: a defect in brain development resulting in small or missing brain hemispheres

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

anencephalia 12 letters wn-def

a defect in brain development resulting in small or missing brain hemispheres

anencephaly 11 letters wn-def

a defect in brain development resulting in small or missing brain hemispheres