PLAGIOCEPHALY - DIFFERENTIAL-DIAGNOSIS BASED ON ENDOCRANIAL MORPHOLOGY

Plagiocephaly is a descriptive term that connotes an asymmetrically ob lique or twisted head. Such cranial dysmorphology has a number of etio logies, the most common of which are unicoronal synostosis, unilambdoi d synostosis, and plagiocephaly without synostosis. Use of the term pl agiocephaly in the literature is often ambiguous in that at times it i s used inclusively for all etiologies while at other times it is used exclusively as a synonym for unicoronal synostosis. Although different iation by physical examination among unicoronal synostosis, unilambdoi d synostosis, and plagiocephaly without synostosis usually is possible for an experienced observer, inexperienced observers often have diffi culty making an anatomically accurate diagnosis even with the assistan ce of conventional skull radiographs. High-resolution CT scans, includ ing three-dimensional osseous surface re-formations, have become a sta ndard element in the evaluation of craniofacial anomalies in many cent ers. We hypothesized that the three major etiologies of plagiocephaly could be unambiguously differentiated by means of endocranial three-di mensional CT osseous surface re-formations. Archival pretreatment CT d ata on 15 unicoronal synostosis, 4 unilambdoid synostosis, and 15 plag iocephaly without synostosis patients were reviewed to define, qualita tively and quantitatively, the characteristics of the endocranial base morphologies for each group; in addition to visual dysmorphology spec ific to each group, there was a statistically significant difference i n the angle of deviation from the midlines of Me anterior and posterio r cranial fossae among unicoronal synostosis, unilambdoid synostosis, and plagiocephaly without synostosis. Four radiologists experienced in reading images of craniofacial anomalies were oriented to the group c haracteristics and then instructed to perform differential diagnosis f or each of the 34 patients using only the endocranial three-dimensiona l CT images. The raters were blind to all other clinical and diagnosti c information. The raters correctly diagnosed unicoronal synostosis. E rrors were made in differentiation of unilambdoid synostosis and plagi ocephaly without synostosis. These errors resulted from the raters' re liance on image inspection rather than quantitation of anteroposterior fossae midline angulation. Such quantitation unambiguously differenti ated between unilambdoid synostosis and plagiocephaly without synostos is in the ''error'' cases. The endocranial base dysmorphology of patie nts with plagiocephaly is etiology-specific for unicoronal synostosis, unilambdoid synostosis, and plagiocephaly without synostosis. Three-d imensional CT endocranial base images can assist differential diagnosi s of plagiocephaly.