Named after the character in Robert Burn’s poem of the same name, a Tam O’Shanter is a Scottish hat (picture here). The appearances of advanced Paget’s disease of the skull are similar.
Other Paget’s disease related signs
blade of grass sign
jigsaw pattern bone or mosaic pattern bone
picture frame vertebra
cotton wool appearance of bone
Other inanimate object inspired signs at Radiopaedia.org here.
S. Smith “Radiologic Spectrum of Paget Disease of Bone and Its Complications with Pathologic Correlation” RadioGraphics. 2002;22:1191-1216
P. Richards “Paget’s Disease Causing an Arnold-Chiari Type 1 Malformation” AJR 2001; 176:816-817
Credit: Dr Frank Gaillard