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

peritumoural fibrous pseudocapsule.
Lesions most commonly have a uniform,
pale grey or tan appearance and a soft
consistency, although they may appear
firm and whorled if a large fraction of the
lesion is composed of mature stromal
elements. Polypoid protrusions of tumour
into the pelvicaliceal system may occur
resulting in a "botryoid" appearance
{1602}. Cysts may be prominent. Rarely,
nephroblastoma occurs in extrarenal
sites {28,1976}.
A
Fig. 1.68 Nephroblastoma. A circumscribed, encapsulated lesion with cyst formation. B Polypoid extension
into renal pelvis.
B
Tumour spread and metastasis
Nephroblastomas generally have a restricted
pattern of metastasis, most commonly
regional lymph nodes, lungs, and liver
{318}. Metastatic sites other than these (i.e.,
bone or brain) are unusual and should suggest
alternative diagnoses.
Table 1.07
Staging of paediatric renal tumours: Children’s Oncology Group (COG) and Societé International d’Oncology
Paediatrique / International Society of Paediatric Oncology (SIOP).
Stage
Definition
I COG: Limited to kidney and completely resected. Renal capsule is intact.
SIOP:
COG & SIOP:
Limited to kidney or surrounded with fibrous pseudocapsule if outside the
normal contours of the kidney.
Presence of necrotic tumour or chemotherapy-induced changes in the renal
sinus or soft tissue outside the kidney does not upstage the tumour in the
post-therapy kidney.
Renal sinus soft tissue may be minimally infiltrated, without any involvement
of the sinus vessels. The tumour may protrude into the pelvic system without
infiltrating the wall of the ureter. Intrarenal vessels may be involved. Fine
needle aspiration does not upstage the tumour.
II COG & SIOP: Tumour infiltrates beyond kidney, but is completely resected.
Tumour penetration of renal capsule or infiltration of vessels within the renal
sinus (including the intrarenal extension of the sinus). Tumour infiltrates
adjacent organs or vena cava but is completely resected. Includes tumours
with prior open or large core needle biopsies. May include tumours with
local tumour spillage confined to flank.
III COG & SIOP: Gross or microscopic residual tumour confined to abdomen.
Includes cases with any of the following:
a) Involvement of specimen margins grossly or microscopically;
b) Tumour in abdominal lymph nodes;
c) Diffuse peritoneal contamination by direct tumour growth, tumour
implants, or spillage into peritoneum before or during surgery;
d) Residual tumour in abdomen
e) Tumour removed non-contiguously (piecemeal resection)
f) Tumour was surgically biopsied prior to preoperative chemotherapy.
SIOP:
The presence of necrotic tumour or chemotherapy-induced changes in a
lymph node or at the resection margins should be regarded as stage III.
IV COG & SIOP: Hematogenous metastases or lymph node metastasis outside the
abdominopelvic region.
V COG & SIOP: Bilateral renal involvement at diagnosis. The tumours in each kidney should
be separately sub-staged in these cases.
Staging
The most widely accepted staging systems
for nephroblastomas rely on the
identification of penetration of the renal
capsule, involvement of renal sinus vessels,
positive surgical margins, and positive
regional lymph nodes; there are
minor differences between the staging
systems utilized by the SIOP and COG.
While bilateral nephroblastomas are designated
as stage V, their prognosis is
determined by the stage of the most
advanced tumour and by the presence
or absence of anaplasia.
Histopathology
Nephroblastomas contain undifferentiated
blastemal cells and cells differentiating
to various degrees and in different
proportions toward epithelial and stromal
lineages. Triphasic patterns are the most
characteristic, but biphasic and monophasic
lesions are often observed. While
most of these components represent
stages in normal or abnormal nephrogenesis,
non renal elements, such as skeletal
muscle and cartilage occur {193}.
The blastemal cells are small, closely
packed, and mitotically active rounded
or oval cells with scant cytoplasm, and
overlapping nuclei containing evenly distributed,
slightly coarse chromatin, and
small nucleoli. Blastemal cells occur in
several distinctive patterns. The diffuse
blastemal pattern is characterized by a
lack of cellular cohesiveness and an
aggressive pattern of invasion into adjacent
connective tissues and vessels, in
contrast to the typical circumscribed,
encapsulated, and "pushing" border
characteristic of most nephroblastomas.
Other blastemal patterns tend to be
cohesive. The nodular and serpentine
blastemal patterns are characterized by
round or undulating, sharply defined
cords or nests of blastemal cells set in a
Nephroblastoma
49