FAT NECROSIS PRESENTING AS OBSCURE ABDOMINAL-MASS - BIREFRINGENT SAPONIFIED FATTY-ACID CRYSTALLOIDS AS A CLUE TO DIAGNOSIS

Aims-To describe the birefringent saponified fatty acid crystalloids s een in pancreatic fat necrosis. Methods-A histological review, includi ng polarising microscopy, of three cases of subacute or subclinical ac ute pancreatitis was performed. Histochemical analysis using Nile blue sulphate for lipid, Holczinger's copper rubeanate for fatty acids, an d Alizarin Red S for calcium was performed in one case. Scanning elect ron microscopy and x-ray energy dispersive spectroscopic microanalysis were performed in two cases. Necropsy pancreatic tissue, surgical arc hival tissue from cases of pancreatitis, and pancreatic and adipose ti ssue permitted to autolyse together in the laboratory, were also exami ned. The autolysed tissue was also examined histochemically. Stained a nd unstained sections were mounted in DPX and Canada balsam. Surgical material showing traumatic fat necrosis was reviewed. Results-In each of the three cases there were subtle clues to subclinical pancreatitis . In neither surgical case was the true nature of the mass apparent to the operator. Histological analysis in all cases showed ghost adipocy tes containing numerous polarising crystalloids, as well as some basop hilic debris. Microanalysis showed calcium but no other substantial he avy element signals. Histochemical analysis showed a labile, polar, ac idic lipid and the crystalloids behaved as calcium salts of free fatty acid, The crystalloids were not seen in archival material mounted in Canada balsam. No crystalloids were seen in traumatic fat necrosis. Co nclusions-Little recognised, strongly birefringent, saponified free fa tty acid crystalloids occurring in pancreatic fat necrosis may survive routine processing, and can point to the origin of obscure mesenteric masses related to subclinical pancreatitis.