In DiGeorge syndrome, the cortical epithelial cells of the thymus fail to develop and the thymus is hypoplastic. As a result, bone marrow-derived T-cell precursors cannot differentiate and functional T-cell production is markedly reduced. The development of B cells (choice A) is not affected in DiGeorge syndrome. Endothelial cells (choice B) forming the vascular walls are not affected by thymic maldevelopment, nor are the cells of myeloid lineage, the macrophages (choice C), and the neutrophils (choice D).

In TGA, the aorta arises from the right ventricle and the pulmonary trunk arises from the left ventricle (choice C). This is the reverse of the normal situation and gives rise to the cyanotic condition in the newborn. The large arteries arise from the truncus arteriosus in the developing heart and thus could not develop from the atria (choices B and D), which are formed from the sinus venosus. The truncus arteriosus and the sinus venosus are at opposite ends of the heart. The ductus arteriosus (choice A) is the vessel that shunts oxygenated blood from the pulmonary trunk to the arch of the aorta in the fetus. It does not give rise to the aorta.

An irregular outline, a thin wall, and the lack of erythrocytes in the lumen characterize lymphatic vessel. Arterioles (choices A and B) have thicker walls and contain erythrocytes. Venules (choice D) are thin-walled but they contain erythrocytes. Capillaries (choice E) are small in diameter and they contain erythrocytes.

This is the secretory portion of the eccrine sweat gland, recognizable by its three cell types. The apical dark cells (arrow 1) are closest to the lumen. The clear or basal cells (arrow 2) and the myoepithelial cells (arrow 3) are located against the basal lamina. Characteristically, these cells are large and the lumen is small. The apocrine sweat gland (choice A) is lined with simple cuboidal epithelium and thus has a large lumen. The dermal papilla (choice B) is formed by fibroblasts, not epithelia. The hair follicle (choice D) is formed by three concentric zones of keratinized cells and does not have a lumen. The sebaceous glands (choice E) are appendages of the hair follicle and their lumen is lined by stratified squamous epithelium.

The posterior inferior cerebellar artery supplies the rostral, dorsolateral medulla. The posterior spinal (choice D) and anterior spinal (choice B) arteries supply dorsal and ventral portions, respectively, of the caudal medulla. The anterior inferior cerebellar (choice A) and superior cerebellar (choice E) arteries supply portions of the pons and mesencephalon.

Arrow 2 points to the abdominal aorta, located anterior to the lumbar vertebra. Arrows 1 (choice A) and 5 (choice B) indicate the left and right kidneys respectively. Arrow 3 points to the inferior vena cava; the junctions of the left and right renal veins to the inferior vena cava are seen in this CT scan. Arrow 4 points to a loop of the small intestine, filled with contrastenhancing material.

Arrow 2 points to the base of the gastric glands where chief or peptic (zymogenic) cells tend to be clustered. Arrow 1 points to the luminal surface of the stomach where mucus-secreting cells are found. Arrow 3 points to the muscularis mucosae. Arrow 4 points to the middle of the gastric glands where parietal or oxyntic cells tend to be most numerous. Arrow 5 point to the side of a gastric pit where mucus-secreting cells are also found.

49) A 62-year-old patient diagnosed with prostate carcinoma complains of a right-sided headache worsening over 4 days and displays a drooping right upper eyelid. Examination reveals a right third nerve palsy. An MRI reveals a single metastasis of the prostatic carcinoma in the right side of the midbrain, causing Benedikt’s syndrome. Which of the following signs would also be seen in this patient?

Benedikt’s syndrome results from a lesion situated in the tegmentum of the midbrain, at the level of the third cranial nerve (oculomotor) nucleus and its associated tracts, as exemplified by ptosis and third nerve palsy in this patient. The red nucleus is also affected at this level giving rise to motor impairment displayed by the intention tremor. Since the rubrospinal tract crosses at the level of the midbrain to project to the opposite side of the body, the tremor will manifest itself contralateral to the side to the lesion. The seventh cranial nerve (facial) nucleus is located in the pons, and the facial musculature (choice A) in this patient would not be affected. Likewise, the twelfth cranial nerve (hypoglossal) nucleus is located in the medulla, and the innervation of the tongue (choice B) would be spared in this patient. A lesion causing a pure Benedikt’s syndrome would be confined to the midbrain tegmentum and not affect the corticospinal tract. Ipsilateral hemiplegia (choice D) would not be present in this patient. Finally, vertical gaze palsy (choice E) results from a lesion or compression of the midbrain tectum and not of the tegmentum.

Long-term exposure to the sun increases the risk of alteration of the DNA structure by cleavage, ionizing radiation, or recombination of DNA with highly reactive free radicals. These changes can result in neoplastic changes or death in skin cells. In the skin, mitosis occurs only in the malpighian layer formed by the stratum basale and the stratum spinosum of the epidermis. The DNA of dividing cells is more vulnerable to the harmful effects of the sun, and neoplastic changes are usually observed in the malpighian layer. They are not seen in the stratum corneum (choice A), stratum lucidum (choice B), or stratum granulosum (choice C). Choice E represents the dermis located below the epidermis, which is the only skin layer considered in this question.

52) A female 44-year-old patient suffers from acute bacterial sinusitis localized to the frontal sinus. The patient displays a mucopurulent greenish discharge from the nose bilaterally, with associated fever and malaise. The patient also complains of pain over the forehead with headache. Which of the following innervates the frontal sinus?