
R. SHAKYA ET AL. 19
The concept of vascular sling was first introduced for
differe nt iation fr om vascular ri ng.
According to the location of the LPS, it is classified
into two types [1]. The type 1 is defined by the location
of the LPS (levels of T4-T5), then regarding the course
of the tracheal bronchus (TB), the type 1 is divided into
subtype 1A (the course of TB is normal) and subtype 1B
(with additional upper TB). Type 2 is defined by a more
caudal location of LPS (level of T6) and then according
to the existence of the right upper lobe bronchus. Type 2
is further classified into subtype 2A (with normal upper
lobe bronchus) and subtype 2B (without existence of
upper lobe bronchus). Because of the lower location of
the LPS, one to three pulmonary lobes are supplied by a
single bronchus arising fr om the left bron chus, and this is
known as “bridging bronchus”. Our case belongs to the
subtype 1B .
Multidetector CT is recent technical advance in helical
CT imaging. It is performed by moving the patient table
through the CT gantry at a constant speed during con-
tinuous scanning with x-ray tube rotating around the pa-
tient and includes multiple rows of detector rings. It al-
lows acquisition of thin multiple slices creating isotropic
voxels from which reconstruction of image can be done
in different anatomic planes without loss of resolution.
CT Angiography is a diagnostic test that uses CT scanner
and contrast materials which is administered as rapid
bolus through a small catheter placed in a vein of the arm.
CT scan is then performed during contrast material flows
through the blood vessels to various organs which will
increase CT numbers of blood vessels and can be isolated
from low density structures producing 3-dimensional
images of the blood vessels and su rrounding tissues after
reconstructed in different planes by usin g c omputer.
Radiologic examinations play an important role in dia-
gnosis of LPS. Usually a multi-modality approach, such
as chest radiograph y, echocardiography, esophagogr aphy,
computed tomography angiography (CTA), and magnetic
resonance angiography (MRA) are used for diagnostic
work-up [2]. CTA and MRA have almost replaced con-
ventional ang iography for diagnosis, and the sens itivities
of these techniques are nearly 100% [3]. Although MRA
has advantage of non-ionizing radiation exposure, MRA
usually needs long scan time requiring deep conscious
sedation or anesthesia in uncooperative children. MRA
also has a limited role in visualization of the airway and
lung parenchyma. However, CTA can reduce the scan
time significantly to nearly 2.0 sec with conventional
helical protocol and 3.95 sec with prospective ECG-gat-
ing protocol as in our case. CTA also has advantage of
evaluating the trachea. CTA shows detailed information
of the relationship between pulmonary artery and airway
with post processing techniques as in this case. CTA is
also helpful in pre-operative evaluation and post-opera-
tive follow-u p [4]. Although CTA bears th e burden of ra-
diation exposure, a variety of techniques had been used
to reduce the radiatio n dose [5].
There are no adverse effects which could be seen in
this patient. But there maybe adverse effect, one is about
the radiation dose, because the children are more sensi-
tive to the radiation dose in comparison to the adult.
However, the benefit from CTA is more than the adverse
effect as mentioned to pre-operation evaluation.
Management of LPS is based on anatomical classifica-
tion and symptoms. Asymptomatic Type 1 patients can
be followed clinically, and those with respiratory symp-
toms are appropriate for surgery [6]. Because of the
lower mortality and morbidity than other techniques,
slide tracheoplasty is currently regarded as the choice of
surgical repair [7].
The prognosis of PAS is variable according to clinical
presentation. Asymptomatic patients have an excellent
prognosis compared with symptomatic patients [8]. Fiore
et al. [9] reported a 79% survival rate in patients with
surgery.
4. Conclusion
CTA with its multi reconstruction techniques is a valu-
able tool for diagnostic, pre-operative evaluation and
post-operative follow-up of LPS.
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