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PRIMARY CARCINOID TUMOUR IN HORSESHOE KIDNEY
RADOSŁAW LITWINOWICZ1, JOANNA SZPOR1, GRZEGORZ JANUŚ2, MAREK WOREK3, KRZYSZTOF OKOŃ1
1Department of Pathomorphology, Collegium Medicum, Jagiellonian University
2Department of Pathology, St. Luke Regional Hospital, Tarnów
3Department of Urology, St. Luke Regional Hospital, Tarnów
Primary renal carcinoid tumours are extremely rare. To date, approximately
60 cases have been reported, mostly as case reports with only few series noted.
The pathogenesis of this tumour is uncertain because neuroendocrine cells are not
found in normal adult renal parenchyma. We report a case of primary renal carci-
noid occurring in a horseshoe kidney in a 66-year-old patient. A clinical, histolog-
ical and immunohistochemical picture of this tumour is presented.
Key words: carcinoid tumour, renal tumour, horseshoe kidney.
Carcinoids are neuroendocrine tumours mostly
found in the gastrointestinal tract (73.7%) and respi-
ratory tract (25.1%) . Other localizations  like
ovary, testis, cervix, biliary duct, breast or gallblad-
der are rare. Primary renal carcinoids are even less
common. To date, approximately 60 cases have been
reported. As neuroendocrine cells are not found in
normal adult renal parenchyma, the histogenesis
remains uncertain. Nevertheless, neuroendocrine
cells may be found during renal embryogenesis 
and some other primary renal tumours were found to
show neuroendocrine features . On gross exami-
nation, renal carcinoids present as single, well demar-
cated, solid, yellow or grey coloured tumours. These
tumours usually spread locally, metastases are rare
but their frequency increases with the increasing
tumour size. The most common are metastases to
lymph nodes and liver.
Material and methods
Clinical data were retrieved from the archive files
of the hospital in Tarnów. The original tumour sam-
ples that had been fixed in the formaldehyde solution,
routinely processed and embedded in paraffin and
stained with haematoxylin and eosin were reviewed.
Immunohistochemistry was performed using a stan-
dard protocol. For antigen retrieval, heating in citrate
buffer (pH 6.0) was used. The following primary anti-
bodies were used: NSE (clone BBS/NC/ VI-H14,
dilution 1 : 100), chromogranin (polyclonal, dilution
1 : 500), synaptophysin (polyclonal, dilution 1 : 500),
CK-7 (clone OV- TL12/30, dilution 1 : 50), CK-
HMW (clone 34βE12, dilution 1 : 50), Ki-67 (clone
MIB1, dilution 1 : 50). All primary antibodies were
manufactured by DAKO (Dako, Denmark). EnVi-
sion (Dako, Denmark) detection system was used.
A 66-year-old man in good general conditions was
Colonoscopy did not show any changes in the colon,
but on lab tests the patient showed anaemia and
thrombocythemia. Results of other laboratory studies
were within normal limits. No signs of the carcinoid
syndrome were reported. Chest radiography did not
reveal any abnormalities. Abdominal ultrasonogra-
phy and computer tomography scans revealed
a horseshoe kidney with a 14 × 6-cm well-circum-
scribed heterogeneous mass. The tumour was located
in the lower pole of the left kidney and in isthmus,
near the aortic area. In the left renal vein, a solid
mass of 9 cm in length was seen; this was interpret-
ed as tumour infiltration. Bilateral urinary retention
was seen, more pronounced on the left side. No lym-
phadenopathy was seen. Based on an intraoperatory
frozen section, the diagnosis of epithelial malignancy
was given. The patient underwent radical nephrecto-
my with lymphadenectomy. Haemodialyses were
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started on the next day after the surgery. The post-
operatory period was uneventful.
Grossly, the resected horseshoe kidney with fused
lower poles measured 17 × 8 × 4.5 cm, and contained
a solid yellow-coloured tumour mass located in the
lower left and central part of the kidney. The tumour
weighed 660 g and measured 8 × 6 × 4 cm. It infil-
trated the left renal pelvis, left renal vein, fibrous cap-
sule and surrounding perinephric fat. Microscopically,
the tumour showed trabecular growth pattern (Fig. 1).
Tumour cells showed moderate polymorphism, narrow
rim of eosinophilic cytoplasm surrounded round nuclei
with granular (“salt and pepper”) chromatin (Fig. 2).
The mitotic index was 10/50 HPF. No necrosis or cal-
cifications were seen. Periaortic lymph nodes showed
deposits with similar histology. Immunohistochemical-
ly, the tumour cells were positive for synaptophysin
(Fig. 3), chromogranin and neuron-specific enolase
(NSE), while stains for CK-7 and CH-HMW were
negative. 5% of tumour cells were positive for Ki-67.
Basing on these findings, the diagnosis of renal
carcinoid was formulated.
Primary renal carcinoids are extremely rare. To
date, approximately 60 cases have been reported. It
is distinctly more frequent in the horseshoe kidney.
The relationship with congenital renal defects is
however not entirely specific, as other tumour types
were also shown to be more frequent in such cases
[4, 5]. Nearly 25% of all carcinoid tumours occur in
the horseshoe kidney . Krishman et al.  calcu-
lated the relative risk (RR) to be 62, and Motta 
– 120. The histogenesis is uncertain since to our
knowledge, neuroendocrine cells are not found in
normal adult renal parenchyma. On the other hand,
they occur in the kidney during embryogenesis [6, 9].
There are several hypotheses about the histogenesis
of renal carcinoids. They might originate from neu-
roendocrine cells found in metaplastic, chronically
inflamed pyelocaliceal urothelium. Alternatively,
they might derive from misplaced pancreatic, intes-
tinal or pulmonary or neural crest-derived neuroen-
docrine cells. Interestingly, carcinoids may coexist
with congenital renal defects; this feature is shared
however with other renal tumours. Multipotential
stem cells could give rise to a carcinoid through acti-
vation of genes responsible for the neuroendocrine
phenotype. Some seemingly primary renal carcinoids
could constitute metastatic focus from an undiscov-
ered primary. Distinction of primary and metastatic
renal carcinoids may be of practical importance but
this may not be achieved by histological examination
Renal carcinoid tumours occur predominantly in
the fifth and sixth decades of life, but some cases
Fig. 1. Trabecular pattern of growth typical of carcinoid
tumour (haematoxylin-eosin, magnification 100×)
Fig. 2. On higher magnification, carcinoid cells are polyg-
onal with eosinophilic cytoplasm, round, rather monomor-
phic nuclei with a granular (“salt and pepper”) chromatin
pattern (haematoxylin-eosin, magnification 400×)
Fig. 3. Tumour cells are positive for synaptophysin
(immunohistochemistry, magnification 100×)
PRIMARY CARCINOID TUMOUR IN A HORSESHOE KIDNEY
PJP 1 2011:Layout 1 2011-05-0514:10 Strona 73
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were reported at the age of 12 years and over the age
of 70 years. Generally, there is no gender predilec-
tion, but carcinoids located in the horseshoe kidney
are more frequent in males (M : F ratio is 1.5 : 1).
The most common clinical symptoms include
abdominal or flank pain, haematuria, fever, weight
loss, and thus do not differ from other renal tumours.
In 28% of cases, a palpable mass is seen. The carci-
noid syndrome is present in 15% of the cases only.
Approximately 25% of patients are asymptomatic
. On imaging studies (CT, MRI, US), renal carci-
noids do not differ from other renal tumours. Renal
cell carcinoma is thus a common preoperative diag-
Grossly, carcinoids are usually single, yellowish to
tan to grey tumours. The reported sizes range from
2 to 17 cm (average 6.4 cm). The lesion is usually
solid, but occasionally may be associated with a cys-
tic component. Although renal carcinoid is usually
well demarcated, in several cases, extrarenal spread
with fat tissue infiltration may be seen and 10%
show vascular invasion. Histologically, the growth
pattern is the same as in other locations: trabecular
or ribbon-like arrangement or solid nests with
peripheral palisading. Stroma is highly vascularized.
Cells are rather monomorphic with granular
eosinophilic cytoplasm and blurred cytoplasmic bor-
ders. Nuclei are round to oval, characteristically uni-
form in size and shape, with coarse chromatin. The
nucleoli are small. Single mitotic figures may be
seen. Calcification, haemorrhage or necrosis are
uncommon. The diagnosis is confirmed by immuno-
histochemistry, with positive reactions for common
neuroendocrine markers such as chromogranin, eno-
lase or synaptophysin .
Metastases occur in about half of all cases; their
typical locations are lymph nodes (92%), liver
(34.5%), bone (9%), lung (2%), spleen (1.8%), gas-
trointestinal tract (1.8%) and kidney (1.8%). This
metastatic pattern is obviously different from most
renal tumours . The size of the primary tumour is
reported to correlate with the incidence of metas-
tases , which can occur as late as 7 years after
treatment . The only treatment modality is par-
tial or radical nephrectomy, accompanied by lymph
node dissection. Chemotherapy is used only in the
case of liver metastases [2, 10]. Because of the
tumour rarity, there is little data on prognosis or
prognostic factor . The main prognostic factor
might be the tumour size, and patients below the
age of 40 years, with a horseshoe kidney, with
a tumour less than 4 cm and in which the rate of
mitoses is less than 1/10 HPF fare better .
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Address for correspondence
Department of Pathomorphology
ul. Grzegórzecka 16
RADOSŁAW LITWINOWICZ, JOANNA SZPOR, GRZEGORZ JANUŚ, ET AL.
THE AUTHOR OF CORRECT DIAGNOSIS IS:
Elżbieta Trojnar MD, Department of Pathomorphology, Provincial Hospital No 2, Rzeszów, Poland
PJP 1 2011:Layout 12011-05-05 14:10 Strona 74