Lipiduria is a recognized feature of the nephrotic times without (Figure 2D). These bodies correspond to the free fatty droplets seen by light microscopy. syndrome. In most nephrotic patients, urinary lipids There is evidence that in nephrotic patients, ultrafilcan be seen by light microscopy [1], either as fatty tered lipids are partially reabsorbed by proximal tubucasts, oval fat bodies (i.e., tubular cells laden with lar cells [4] and transported for hydrolysis into lipids), free fatty droplets, or cholesterol crystals [2]. lysosomes [5,6 ]. Thus, we believe the fatty cells found Transmission electron microscopy, which is done on in the urine are tubular cells which have been sloughed ultra-thin sections of pelleted urine and shows the from the tubular basement membrane after reabsorpinternal substructures, adds interesting details to light tion of ultrafiltered lipids [4]. The intracellular memmicroscopy findings. In tubular cells laden with lipids, brane-bound bodies are nothing but fatty lysosomes. fatty droplets appear as packed round particles which Urinary free fatty bodies are fatty lysosomes derived may entirely occupy the cytoplasm (Figure 1A). As in either from active expulsion from the tubular cells [4] other organs [3], the fatty droplets are either electron or cellular breakdown. Several studies have shown that lucent or electron dense [Figure 1A], or show a perithe microscopically visible lipid droplets, either cellular pheral medium dense halo and clear centre or noncellular, mainly contain cholesterol esters [4,7]. (Figure 1B), which is known as ‘annular lipid inclusion’ [3]. Several factors may influence these different appearances such as the type of fixation, the tissue References preparation, or the saturated and unsaturated fatty 1. Ravigneaux M-H, Pellet H, Colon S et al. Signification d’une acid content [3]. Intermingled with fatty droplets, cytolipidurie dans le cadre d’un syndrome nephrotique. cytoplasmic clefts can also be seen (Figure 1C, D), Nephrologie 1991; 12: 12–16 which are due to cholesterol crystals. 2. Fogazzi GB, Passerini P, Ponticelli C, Ritz E. The Urinary In other cells, fatty droplets are clumped into memSediment. An Integrated View. Chapman & Hall, London, 1994; 46–48 brane-bound bodies of variable diameter (0.7–2.2 mm), 3. Ghadially FN. Ultrastructural Pathology of the Cell and Matrix which are scattered throughout the cytoplasm (2nd edn). Butterworths, London, 1982; 280–283, 380–383, (Figure 2A). At high magnification, they contain many 716–719 medium dense fatty droplets of variable sizes, heaped 4. Zimmer JG, Dewey R, Waterhouse C et al. The origin and nature of anisotropic urinary lipids in the nephrotic syndrome. Ann one upon another (Figure 2B). Interestingly, similar Intern Med 1961; 54: 205–214 bodies can also be seen free in the urine, sometimes 5. Peterson DR, Hjelle JT, Carone FA, et al. Renal handling of surrounded by a membrane (Figure 2C), but at other plasma high density lipoprotein. Kidney Int 1984; 26: 411–421 6. Saku K, Sata S, Naito S et al. Apolipoproteins in human biopsied nephrotic kidneys. Int Urol Nephrol 1988; 20: 429–438 Correspondence and offprint requests to: GB Fogazzi, Divisione di 7. Martin RS, Small DM. Physicochemical characterization of the Nefrologia e Dialisi, Ospedale Maggiore, IRCCS, Via Commenda urinary lipid from humans with nephrotic syndrome. J Lab Clin Med 1984; 103: 798–810 15, 20122 Milano, Italy.
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