QUESTION: 53

A gang member is rushed to the emergency room suffering from multiple stab wounds made by an ice pick. Athird-year medical student rotating through emergency medicine is puzzled by the sight of a milky white substance exuding from a stab wound just superior to the right sternoclavicular joint. Which of the following structures is possibly injured at this location?

the common carotid artery
the cupola of the right lung
the internal jugular vein
the right lymphatic trunk
the thoracic duct

Answer(s): D

Explanation:

The right lymphatic trunk is ruptured and chyle is exuding from the wound. Blood would flow from a wound involving the common carotid artery (choice A) or internal jugular vein (choice C). Astabbing lesion of the cupola of the right lung (choice B) would result in pneumothorax. The thoracic duct (choice E) does carry chyle. However, the thoracic duct drains into the bifurcation of the internal jugular and subclavian veins on the left side, above the left sternoclavicular joint.

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QUESTION: 54

A 72-year-old male patient has suffered a cerebral infarct affecting the left cerebral hemisphere. On examination of the patient, it is noticed that his verbal output is fluent and paraphasic. His comprehension of speech is normal but repetition is severely impaired. Naming is also impaired, although when given a list, the patient is able to select the correct name. Special consultation with a neurologist results in a diagnosis of conduction aphasia. Which of the following brain structures is affected?

arcuate fasciculus
Broca's area
nucleus ambiguous
red nucleus
Wernicke's area

Answer(s): A

Explanation:

The arcuate fasciculus connects Wernicke's area to Broca's area, integrating comprehension of speech with motor speech. A lesion in this connecting bundle results in this unusual condition of conduction aphasia, characterized by impairment of repetition and naming. Broca's area (choice B) is the motor speech area and lesion in this area will result in motor speech impairment. However, this patient's verbal output is fluent. Alesion in the nucleus ambiguus (choice C) will result in dysarthria and also loss of a fluent verbal output. The red nucleus (choice D) is a mesencephalic motor nucleus, which does not participate in the central pathways for speech. Wernicke's area (choice E) is the speech comprehension area, which is intact in this patient because he comprehends spoken language.

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QUESTION: 55

Which of the following is characterized by an absence of lymphoid follicles and germinal centers?

axillary lymph node
Peyer's patches
pharyngeal tonsil
spleen
thymus

Answer(s): E

Explanation:

The thymus provides for development of new T lymphocytes in an environment shielded from foreign antigens. Like bone marrow, the thymus is a primary lymphoid organ, and not a site of reactions to foreign antigens. Lymphoid follicles are sites of B lymphocyte proliferation in response to antigen stimulation.
These occur in the lymph nodes (choice A), Peyer's patches (choice B), tonsils (choice C), and white pulp of the spleen (choice D).

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QUESTION: 56

A 24-year-old student is brought to the emergency room after being found in a ditch where he had lain overnight after being hit by a car. He complains of severe pain in the left arm and examination reveals a broken humerus. Neurological examination reveals that the patient can extend the elbow but displays inability to supinate the elbow when it is extended. The patient also has wrist drop and very weak hand grasp. The neurological lesion is likely localized at which of the following locations?

posterior cord of the brachial plexus
posterior divisions of the brachial plexus
radial nerve at the distal third of the humerus
radial nerve at the midforearm
radial nerve at the wrist

Answer(s): C

Explanation:

Wrist drop and weak hand grasp indicate that the patient has a lesion of the radial nerve, most likely at the distal third of the humerus, sparing the innervation of the tríceps brachii but affecting the supinator.
Because the patient can extend the elbow, the integrity of the posterior cord (choice A) and posterior divisions (choice B) of the brachial plexus is preserved. Lesion of the radial nerve at the midforearm (choice D) and wrist (choice E) would spare the innervation of the supinator.

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