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

Fig. 1.61 Metanephric adenofibroma. Note epithelial area which is identical to metanephric adenoma (bottom), and stromal component which is identical to
metanephric stromal tumour (top).
Metanephric stromal tumour
P. Argani
Definition
Metanephric stromal tumour is a rare
benign paediatric renal neoplasm, which
is identical to the stromal component of
metanephric adenofibroma {110,1075}.
ICD-O code 8935/1
Clinical features
Metanephric stromal tumour (MST) is
approximately one-tenth as common as
congenital mesoblastic nephroma {110,
120}. The typical presentation is that of
an abdominal mass, though haematuria
is not uncommon and rare patients may
present with manifestations of extra-renal
vasculopathy such as hypertension or
haemorrhage. Mean age at diagnosis is
24 months. A rare adult tumour has been
identified {255}.
Macroscopy
MST is typically a tan, lobulated fibrous
mass centred in the renal medulla. Mean
diameter is 5 cm. Approximately one-half
of cases are grossly cystic, while onesixth
are multifocal.
Histopathology
MST is an unencapsulated but subtly
infiltrative tumour of spindled to stellate
cells featuring thin, hyperchromatic
nuclei, and thin, indistinct cytoplasmic
extensions. Many of the characteristic
features of MST result from its interaction
with entrapped native renal elements.
MST characteristically surrounds and
entraps renal tubules and blood vessels
to form concentric "onionskin" rings or
collarettes around these structures in a
myxoid background. More cellular, less
myxoid spindle cell areas at the periphery
of these collarettes yield nodular variations
in cellularity. Most tumours induce
angiodysplasia of entrapped arterioles,
consisting of epithelioid transformation of
medial smooth muscle and myxoid
change. Rarely, such angiodysplasia
Fig. 1.62 Metanephric stromal tumour. Note the
nodular appearance.
Fig. 1.63 Metanephric stromal tumour. Note juxtaglomerular
cell hyperplasia.
46 Tumours of the kidney