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A Case of Equine Embryonal Nephroma
DIAGNOSIS AND DISCUSSION
The gross microscopical picture of the tumour is at once suggestive of an
adenocarcinoma and in the absence of sufficient information, material or de-
liberation one would feel justified in diagnosing the tumour as such. A closer
examination would, however, reveal the presence of a sarcomatous cellular
moiety and demonstrable stages in the derivation therefrom of more or
less drawn out glandular structures. If one adds to this the presence of well-
formed, interspersed trabeculae of connective tissue, one is compelled to desist
from giving the verdict in favour of a carcinoma. The nearest approach
to a histologically correct diagnosis would be the designation adenosarcoma
a term which has been employed on more than one occasion to describe tumours
similar to the one under study. If one considers the clinical and autopsy
records, and the complex nature of the growths, a more definite diagnosis of
embroynal nephroma seems inevitable. The available information points
to the fact that the primary tumour was the one which hung down into the
peritoneal cavity on the left side and in. which the left kidney was presumably
absorbed. The hydronephrotic change in the other kidney, the duration
and nature of illness, and the extensive peritoneal metastasis indicate
that the neoplasia was of some duration, the primary tumour gradually inter-
fering with the function of the left kindey and ultimately replacing it.
In human beings embryonal nephromata are most commonly met with
in. children and are generally known as Wilm's tumours. There is reason to
suppose that these are derived from embryonal cells which have separated
from the mesoblast at or about the time of the formation of the renal blastema,
but have lain dormant until the time when, due to some exciting cause or due
to the disappearance of the restraining influence, the cells have assumed neo-
plastic propensities and started to proliferate. The resulting growth is always
a mixed one, the degree of heterogeneity of the constituent tissue elements
depending upon the stage at which the neoplastic cell-rest was formed. It is
not at all difficult to appreciate the fact that a cell at an early stage in ontogeny
is less differentiated and thus, as a rule, possesses the power to produce a variety
of histological structure. This is particularly true in the case of mesodermal
cells from which are normally derived widely dissimilar structures, so that " the
more embryonic and less differentiated the cells from which the tumour origi-
nates, the more complicated will the structure be because of the multipotency
of the undifferentiated mesodermal cells " [Wollstein, 1927]. Naturally, the
resulting tumour is most often of the nature of a teratoma. In some of the
tumours (e.g., of children and pigs), obviously arising from rests derived rather
early in ontogeny, striped muscle, cartilage and even bone have been observed.
In such tumours due to lack of differentiation and organization, the resem-
blance of the resulting growth to the adult kidney is relatively less noticeable.
One need not wonder, therefore, at the inconstancy of the component tissues or
at the lack of uniformity of the histological picture met with in embryonal
nephromata because the qualitative as well as the quantitative composition
of the growth must depend upon the stage at which the tumour cells have be-
come detached from the parent germ-layer.