Abnormality of the philtrum Midline sinus of philtrum 2012-05-01T10:36:55Z Although congenital sinuses of the lips generally occur in the lower lip, in rare instances they may appear in the philtrum of the upper lip, commonly close to the insertion of the columella. Central sinus of philtrum Pit in the midline of the philtral groove. Philtrum, Midline Sinus UMLS:C4021116 HP:0011828