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usmle step 1 question bank(u world anatomy- 100 questions)
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100 anatomy usmle question bank from u world
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ANATOMYThe following vignette applies to the next 2 items.
A 52 year old man is brought to the emergency department for
evaluation of fever, chills and malaise. Cardiac examination reveals a
new holosystolic heart murmur that radiates towards the axilla. Blood
cultures are obtained and he undergoes transesophageal
echocardiography. The ultrasound probe is placed in the mid-esophagus
facing anteriorly and cardiac chambers are interrogated.
1. Anatomically, which of the following chambers is closest to the
probe?
A. Left atrium
B. Left ventricle
C. Right atrium
D. Right ventricle
Answer: A. left atrium
Explanation:
,This patient’s presentation suggests acute endocarditis, with
confirmation pending the results of the blood cultures and cardiac
imaging. Transesophageal echocardiography (TEE) uses ultrasound
waves generated from within the oesophagus to produce clear images of
neighbouring cardiac structures. The left atrium makes up the majority of
the heart’s posterior surface, with the oesophagus passing immediately
posterior to the heart. Therefore, the oesophagus lies within closest
proximity to the left atrium. This allows the left atrium, atrial septum and
mitral valve to be particularly well visualised on TEE. due to its adjacent
proximity, conditions that result in left atrial enlargement (eg. atrial
fibrillation, mitral stenosis) can cause dysphagia through external
compression of the oesophagus.
,Choice B: the left ventricle forms the apex and left border of the heart on
frontal chest x-ray.
Choice C: The right atrium, along with the superior vena cava, forms the
right lateral cardiac border on frontal chest x-ray.
Choice D: the right ventricle forms the anterior (sternal) surface of the
heart and the majority of its inferior border.
Educational objective:
The left atrium forms the majority of the posterior surface of the heart
and resides adjacent to the oesophagus. Enlargement of the left atrium
can compress the oesophagus and cause dysphagia.
2. In the same mid-oesophageal position, the probe is rotated so that it
now faces posteriorly. Anatomically, which of the following will be best
interrogated in this position?
A. Descending aorta
B. Pulmonary artery
C. Pulmonary veins
, D. Superior vena cava
E. Tricuspid valve
Answer: A
Explanation:
The aorta has four major divisions; the ascending aorta, the aortic arch,
the descending thoracic aorta and the abdominal aorta. The ascending
aorta lies posterior and to the right of the main pulmonary artery. The
aortic arch travels above the right pulmonary artery and the left
bronchus. The brachiocephalic, left common carotid, and left subclavian
arteries originate (in that order) from its superior aspect. The descending
thoracic aorta abuts the left anterior surface of the vertebral column and
lies posterior to the oesophagus and the left atrium. This permits clear
visualisation of the descending aorta during transesophageal
echocardiography (TEE), allowing for the detection of abnormalities such
as dissection or aneurysm. The descending thoracic aorta continues to
travel down the left anterior surface of the vertebral column, becoming
the abdominal aorta as it crosses the diaphragm and eventually
branching into the common iliac arteries.
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