During an anatomic dissection of the posterior mediastinum, an unusual
course of the interazygos v. was noted. The hemiazygos v. ascended to
the 8th thoracic vertebra, in front of the vertebral column. It left
the column, ascending obliquely, and passing in front of the aorta and
behind the oesophagus. This transverse segment, crossing the midline,
is called the interazygos v. It may be confused with different lesion
s situated at this level: aneurysm, tumour or lymph node hypertrophy,
during CT or MRI studies. Secondly, the surgeon must be aware of this
azygos variation as a possible cause of haemorrhage during a procedure
in this region.