27
Kidneys, Adrenals, and Retroperitoneum
Fig. 27.1 Glomerulus (inset, top) and high magnification of proximal
tubule epithelium (inset, bottom) juxtaposed on normal renal parenchyma.
proximal tubules. Dark cytoplasmic granules may be demon-
strated on Romanowsky stains in cells most probably derived
from the ascending loop of Henle or distal convoluted tubules.
The cells of the collecting tubules of the medulla are cuboid and
sharply defined (Fig. 27.2).
Imm unocytochem istry of Normal Kidney Structures
In the non-neoplastic kidney, proximal tubules have been
shown to stain with renal cell carcinoma marker antigen (RCC
Ma), particularly at the brush border.
Strong granular cytoplasmic reactivity is seen in proximal
tubular epithelial cells with alpha-methylacyl-coenzyme A race-
mase (AMACR) and less intense staining in distal tubules. CD15
(Leu-M1) stains positively in the cytoplasm of proximal but not
distal tubules, collecting ducts and glomeruli. CD10 stains the
proximal tubular cells in a strong membranous pattern with
luminal accentuation. Cytokeratin (CK)-7 stains the distal con-
voluted tubular cells but not proximal tubules or glomeruli.
Kidney-specific (Ksp) cadherin is expressed in distal convoluted
tubules and thick loops of Henle.16
Renal Cysts
Cysts of the kidney are among the most common mass lesions
to be aspirated, their incidence in three large consecutive FNA
series ranging in frequency from 15 to 43%.17,18 Renal cysts may
be congenital or acquired, the former resulting from disordered
embryogenesis involving cystic enlargement at various sites of
the renal tubular system.19 The diagnosis of congenital cysts
rests largely on evidence of genetic transmission, the age of the
patient, associated congenital abnormalities, and the gross and
microscopic features of the renal cysts.20
Congenital Cysts
Polycystic disease of the kidney may be of the infantile or adult
type, both being inherited forms of cystic disease, usually involv-
ing both kidneys. Numerous thin-walled unilocular cysts of
various sizes lined by flattened epithelial cells involve the renal
parenchyma and contain clear fluid. The adult form is usually
clinically silent until the fourth decade of life, when patients
Fig. 27.2 Normal renal cortical parenchyma showing a variegated
pattern of lighter staining proximal convoluted tubules with darker staining
distal convoluted tubules and collecting ducts (Papanicolaou x MP)
(inset). Higher magnification of proximal tubular epithelium; note
granular cytoplasm and inconspicuous nucleoli. Fine-needle aspiration
(Papanicolaou x HP).
may present with gradual onset of renal failure. The disorder
may occasionally be manifested clinically as lithiasis, flank pain
caused by bleeding into a cyst, or ureteral obstruction caused by
a blood clot.
Fine-needle aspiration results in variable amounts of clear or
pale amber fluid containing a few foamy macrophages.
Acquired or Sim ple Cysts
Most simple cysts are clinically insignificant; they are discov-
ered incidentally during the course of radiologic studies such
as intravenous urograms for unrelated urologic symptoms.
Because these lesions are amenable to conservative therapy and
may not be accurately diagnosed radiologically, FNA has been
advocated for all renal masses thought to be renal cysts. They
commonly have a subcapsulary location, may be multiple, and
may be several centimeters or more in diameter. Histologically,
they are lined by a flat epithelium overlying a thin fibrous wall
and contain fluid that is usually clear and amber-colored, con-
sistent with a transudate. Cytologic examination of the fluid
usually reveals a few benign cuboid cells and an occasional neu-
trophil. Fragments of degenerated epithelial cells should not be
mistaken for carcinoma. Rarely, simple cysts are discolored or
grossly bloody, in which case hemosiderin-laden macrophages
may be seen in addition.
Very rarely, rings resembling parasitic ova and characterized
as Liesegang structures have been encountered in FNAs of renal
hemorrhagic cysts.21 Numerous spheric double-walled structures
with radial striations ranging in size from 8 to 200 pm may be
encountered. It is most important from a therapeutic standpoint
to differentiate these structures from kidney parasites such as
Dioctophyma renale,
which they may simulate. Unlike
D. renale,
Liesegang structures are CK-negative and are seen to have a fibril-
lary composition on ultrastructural analysis.
Association of Renal M alignancy with Renal Cysts
Coexistence of a cyst and carcinoma in the same kidney has
been reported in approximately 2.3-7% of surgically explored
renal cysts.22 Four possible associations of a renal tumor and
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