OK, a truncular vein must be a main large vein, like the jugular or azygous. Smaller veins flow into truncular veins. Have I got this right ?
I found this doing a google search; Truncular refers to vascular lesion that develop later in the embryo development stage so it doesn't refer to the vessel size but only to the vessel origin.
"The current classiﬁcation scheme divides venous malformations into two broad categories: truncular and extratruncular.
Extra-truncular venous malformations originate from
remnants of primitive vessels early in development
and tend to be dysplastic and diffusely inﬁltrative.
Truncular venous malformations originate from a
differentiated vascular truncus at a later stage of
development and are more deﬁned. These two
malformation types tend to have very different
clinical presentations. Truncular venous malformations often have very
impressive cutaneous manifestations in the form
of prominent varicosities and limb swelling. This
is typically caused by retrograde ﬂow of venous
blood in the dilated valveless venous channels of
the malformation. When the malformation is focal
and small, the degree of reﬂux is minimal and
patients usually do not have any signiﬁcant
symptoms other than some cutaneous varicosities.
Larger focal malformations can cause signiﬁcant
reﬂux and symptoms are almost entirely related
to this process. In the lower extremity, focal
truncular malformations frequently connect to
both the deep and superﬁcial venous system. In
this setting, retrograde ﬂow, or reﬂux, from the
deep system into normal superﬁcial veins is the