Eble JN, Sauter G., Epstein JI, Sesterhenn IA - iarc

Metanephric adenoma and metanephric
adenofibroma
J.N. Eble
D.J. Grignon
H. Moch
Definition
Metanephric adenoma is a highly cellular
epithelial tumour composed of small, uniform,
embryonic-appearing cells.
ICD-O codes
Metanephric adenoma 8325/0
Metanephric adenofibroma 9013/0
Metanephric adenosarcoma 8933/3
Epidemiology
Metanephric adenoma occurs in children
and adults, most commonly in the fifth
and sixth decades. There is a 2:1 female
preponderance {561}. Patients with
metanephric adenofibroma have ranged
from 5 months to 36 years (median = 30
months) {120}. There is a 2:1 ratio of males
to females. A single case of high grade sarcoma
arising in association with
metanephric adenoma (metanephric
adenosarcoma) has been reported {2072}.
Clinical features
Approximately 50% of metanephric adenoma
are incidental findings with others
presenting with polycythemia, abdominal
or flank pain, mass, or hematuria.
Presenting symptoms of metanephric
adenofibroma have included polycythemia
or hematuria; some have been
incidental findings. Arroyo et al. {120}
described several cases in which either
Wilms tumour or carcinoma occurred in
association with metanephric adenofibroma.
Other than one patient with
regional metastases from the carcinoma,
these patients have had no progression.
Macroscopy
Metanephric adenomas range widely in
size; most have been 30 to 60 mm in
diameter {561}. Multifocality is uncommon.
The tumours are typically well circumscribed
but not encapsulated. The
cut surfaces vary from grey to tan to yellow
and may be soft or firm.
Foci of haemorrhage and necrosis are
common; calcification is present in
approximately 20%,and small cysts in
10% {561,1237}.
Metanephric adenofibromas are typically
solitary tan partially cystic masses with
indistinct borders {120}.
Histopathology
Metanephric adenoma is a highly cellular
tumour composed of tightly packed
small, uniform, round acini with an
embryonal appearance. Since the acini
and their lumens are small, at low magnification
this pattern may be mistaken for
a solid sheet of cells. Long branching
and angulated tubular structures also are
common. The stroma ranges from inconspicuous
to a loose oedematous stroma.
Fig. 1.57 Metanephric adenoma.
Hyalinized scar and focal osseous metaplasia
of the stroma are present in 10-
20% of tumours {561}. Approximately
50% of tumours contain papillary structures,
usually consisting of tiny cysts into
which protrude blunt papillae reminiscent
of immature glomeruli. Psammoma
bodies are common and sometimes
numerous. The junction with the kidney is
usually sharp and without a pseudocapsule.
The cells of metanephric adenoma
are monotonous, with small, uniform
nuclei and absent or inconspicuous
nucleoli. The nuclei are only a little larger
than those of lymphocytes and are round
or oval with delicate chromatin. The cytoplasm
is scant and pale or light pink.
Mitotic figures are absent or rare.
Metanephric adenofibroma is a compos-
A
B
Fig. 1.58 Metanephric adenoma. A Well circumscribed tumour without encapsulation. B Complicated ductal architecture with psammoma bodies.
44 Tumours of the kidney