noun, masculine/kebɾaˌdeɾo de kaˈbeθa/plural: quebraderos de cabeza
quebradero de cabeza is masculine in Spanish.
headache, worry
“Empezando por las residencias de mayores, que continúan siendo el principal quebradero de cabeza de Downing Street.” — Starting with the nursing homes, which are still the main headache for Downing Street.
Literally, “head breaker”.