Large posterior fontanelle abnormal posterior fontanelle morphology large posterior fontanelle 2017-11-13T09:54:33Z wide posterior fontanelle MP:0030387 enlarged occipital fontanelle large open posterior fontanelle enlarged lambdoid fontanelle an abnormally increased size of the triangle-shaped membranous interval between the pair of parietal bones and the occipital bone for age-related norms; the posterior fontanelle is located at the lambda, at the junction between the sagittal suture and the lambdoid suture large posterior fontanel MPheno.ontology wide open posterior fontanelle large lambdoid fontanelle large lambdoid fontanel large occipital fontanel enlarged posterior fontanelle large occipital fontanelle large fontanelles increased size of the posterior fontanelle