Page 206 - Clinical Manual of Small Animal Endosurgery

194 Clinical Manual of Small Animal Endosurgery

for the thoracic duct ligation. Two 5 mm laparoscopy ports are inserted:
one for insufflation and insertion of the laparoscope/thoracoscope, the
other for insertion of a pair of atraumatic grasping forceps. These are
used to isolate and grasp a mesenteric lymph node for Methylene blue
injection via a percutaneous spinal needle. The technique is advantageous
to the injection of aqueous radiographic contrast agents (lymphangiog-
raphy). In fact, these clear more rapidly, are not visible on thoracoscopy, and
need operating-room fluoroscopy via a c-arm, or radiography.
With an alternative technique, demonstrated by MacDonald et al.
(2008) in a canine cadaver study, all the tissue dorsal to the aorta and
ventral to the vertebrae, including the azygous vein, is ligated en masse
by means of an extracorporeal Meltzer knot, using non-absorbable
braided synthetic suture material. The ligation is performed as far cau-
dally in the chest as possible. The port placement and approach are as
for the thoracoscopic thoracic duct ligation technique. The advantages
to this method are that it is less time-consuming and also less invasive
than dissection and ligation combined with laparotomy/laparoscopy for
mesenteric lymph node injection or lymphangiography. A concurrent
subtotal pericardiectomy is still advised. True efficacy of this technique
in a series of chylothorax dogs has yet to be reported.

Vascular ring anomalies

Vascular ring anomalies causing a megaoesophagus are ideally suited to
a minimally invasive endosurgical approach. It must be borne in mind
that while a persistent right aortic arch (PRAA) is the most common
form of vascular ring anomaly, it is not the only one. In the author’s
experience it is not uncommon to find a PRAA accompanied by an aber-
rant left subclavian artery that, if not also sectioned, will not result in
resolution of the oesophageal constriction.
As these patients are often very small due to their young age, adequate
operating space is a real limitation. While patients may be managed
medically to allow them to grow before surgery, this carries the risks of
developing megaoesophagus, oesophagitis and aspiration pneumonia,
and this should be considered in when making the decision. It is the
author’s preference to operate early in patients over 3 kg in body weight.
While a 5 mm endoscope can still be used in many cases, 3 mm instru-
ments really are preferable, and are absolutely essential in small patients.
If attempting to use larger 5 mm instruments there is sometimes not suf-
ficient space to even open the jaws. Longer instruments are also awkward
to handle, and not precise enough for accurate careful dissection and so
short 20 cm-shafted instruments are required.
Not all puppies with regurgitation after weaning and a dilated cranial
oesophagus on barium contrast studies have a PRAA. The base of the
heart forms a natural elevation to an idiopathic dilated megaoesophagus
and this can appear identical to a vascular ring anomaly on lateral radio-