USMLE : Pathology Practice Test! Trivia Quiz

Explanation
The correct answer is E. This patient presents with signs and symptoms of Wernicke’s encephalopathy (confusion, ophthalmoplegia, and ataxia) and Korsakoff’s psychosis (personality change, confabulation, and memory loss). This syndrome is secondary to thiamine deficiency and commonly seen in malnourished alcoholics. On postmortem examination, patients suffering from Wernicke-Korsakoff syndrome commonly present with symmetric lesions in the paraventricular regions of the thalamus and hypothalamus, mammillary bodies, and periaqueductal region of the midbrain. Answer A is incorrect. Atrophy of the caudate nucleus is found in Huntington’s disease, a disease of autosomal dominance associated with chorea and dementia. Answer B is incorrect. Depigmentation within the substantia nigra pars compacta is commonly seen in Parkinson’s disease, not thiamine defi ciency. Answer C is incorrect. Neurofi brillary tangles, composed of abnormally phosphorylated tau protein, are commonly found in the frontal and temporal lobes of patients with Alzheimer’s disease. Answer D is incorrect. Thiamine deficiency is associated with neuropathologic changes observed on postmortem examination.

Explanation
The correct answer is C. This patient has a lesion consistent with glioblastoma multiforme
(GBM), which is the most common primary brain tumor and is characterized on CT by a
serpentine border and central areas of necrosis.
The diagnosis should be confi rmed by MRI with and without contrast. The lesion consists
of highly malignant astrocyte tumor cells that surround areas of necrosis; this is known as
pseudopalisading. GBM has been associated with genetic alterations, including loss of p53
function, increased activity of the epidermal growth factor receptor gene (EGFR), and loss
of heterozygosity on chromosome arm 10q.
GBM has a poor prognosis, with a mean survival of 8–10 months after diagnosis; most patients
die within 2 years.
Answer A is incorrect. Densely packed cells with halos of cytoplasm surrounding large
round nuclei are characteristic of oligodendrogliomas, which are slow-growing tumors originating
in the cerebral hemispheres. These lesions have a better prognosis than astrocytomas,
with a mean patient survival of 5–10 years.
Answer B is incorrect. Perivascular pseudorosettes with tumor cells surrounding vessels are
characteristic of ependymomas, which are tumors located in the periventricular space or in
the spinal cord that may obstruct the flow of cerebrospinal fluid.
Answer D is incorrect. Sharply demarcated areas of tumor cells located at the grey-white
matter junction are characteristic of secondary metastatic lesions from a primary tumor elsewhere
in the body, most commonly the breast, lung, thyroid, skin, kidney, and gastrointestinal tract.
Answer E is incorrect. A whorled pattern of concentrically arranged spindle cells with calcified psammoma bodies is characteristic of meningiomas, which are the second most common
primary intracranial neoplasm. Meningiomas are benign, slow-growing tumors of the meninges.

Explanation
The correct answer is C. The tissue section shown demonstrates the presence of a Lewy body, which is a cytoplasmic inclusion consisting of aggregated α-synuclein, ubiquitin, tubulin, and neurofi lament proteins. The Lewy body is believed to result from disrupted proteasomal activity, leading to the accumulation of cellular proteins, which results in the disruption of normal cellular processes. Lewy bodies present in the substantia nigra, in the context of a movement disorder (evidenced by this patient’s history and the presence of a deep brain stimulator), are highly suggestive of Parkinson’s disease.

Answer A is incorrect. Guillain-Barré syndrome is a demyelinating disease of the peripheral
nervous system. Lewy bodies are not present.
Answer B is incorrect. Huntington’s disease is an autosomal dominant disease involving atrophy
of the caudate nucleus. It is a progressive, terminal neurodegenerative disorder characterized
by chorea and dementia. Lewy bodies are not present.
Answer D is incorrect. Pick’s disease is a neurodegenerative disease characterized by progressive
dementia, aphasia, and parkinsonism.
Pick bodies (intracellular inclusions of aggregated tau protein), not Lewy bodies, are present
in affected patients.
Answer E is incorrect. Werdnig-Hoffmann disease (also known as spinal muscular atrophy) is
an autosomal recessive disease involving progressive degeneration of the anterior spinal
horns. Lewy bodies are not present.

Explanation
The correct answer is E. This patient has classic findings associated with Turner’s syndrome, a genetic disorder resulting from a 45,XO complement of chromosomes. Approximately 25%–30% of patients will have associated renal anomalies, including horseshoe kidney, pelvic kidney, or duplicated collecting systems. Patients with horseshoe kidneys are approximately four times more likely to develop Wilms’ tumor when compared to the general population.
Answer A is incorrect. Although it has been suggested that patients with Turner’s syndrome
are at increased risk of developing malignancy, they do not have a specifi c increased risk of developing neuroblastoma.
Answer B is incorrect. Although it has been suggested that patients with Turner’s syndrome
are at increased risk of developing malignancy, they do not have a specifi c increased risk of developing ovarian cancer. Familial BRCA gene mutations or no history of childbirth each increases
the risk of ovarian cancer.
Answer C is incorrect. Although it has been suggested that patients with Turner’s syndrome
are at increased risk of developing malignancy, they do not have a specifi c increased risk of developing transitional cell carcinoma. Smoking greatly increases the risk of transitional cell carcinoma.
Answer D is incorrect. Although it has been suggested that patients with Turner’s syndrome
are at increased risk of developing malignancy, they do not have a specific increased risk of developing uterine cancer. Unopposed estrogen secretion (eg., hormone replacement therapy
without progesterone) increases the risk of uterine cancer.

Explanation
The correct answer is C. This patient has transitional cell carcinoma of the bladder, as evidenced
by his painless hematuria and absent signs of prostate cancer. Histology confirms the diagnosis with the presence of invasive transitional cells and prominent, atypical nuclei and mitotic spindles. Numerous factors increase the risk of developing transitional cell carcinoma, the most signifi cant of which is an extensive history of cigarette smoking. Cigarette smoking increases a patient’s risk by three- to sevenfold. Treatment of transitional cell carcinoma largely depends on the stage of disease,
although these tumors have a tendency to recur regardless of disease stage. Low-grade lesions
may be treated with excision, whereas higher-grade lesions require a combination of excision and chemotherapy.

Answer A is incorrect. Aniline dye exposure (eg., in a textile mill worker) is a risk factor for the development of transitional cell carcinoma; however, smoking is the most significant risk factor.
Answer B is incorrect. Cyclophosphamide therapy (eg., in a patient with a history of treated Ewing’s sarcoma) is a risk factor for the development of transitional cell carcinoma; however, smoking is the most signifi cant risk factor.
Answer D is incorrect. Pelvic irradiation (eg., in a patient treated for prostatic cancer) is a risk factor for the development of transitional cell carcinoma; however, smoking is the most signifi cant risk factor.
Answer E is incorrect. Schistosomiasis infection (eg, in a patient with travel to an endemic area, including the Middle East) is a risk factor for the development of transitional cell carcinoma;
however, smoking is the most significant risk factor.

Explanation
The correct answer is C. This patient has symptoms consistent with hemophagocytic lymphohistiocytosis (HLH), and bone marrow aspiration (demonstrating macrophages engulfing
RBCs) confi rms the diagnosis. Familial-type HLH is an autosomal recessive defect in several
genes, including perforin-related genes; the secondary type is frequently due to infection with
Epstein-Barr virus. HLH involves the abnormal activation and proliferation of lymphohistiocytes
leading to hemophagocytosis and the upregulation of proinfl ammatory cytokines. Treatment
consists of a combination of etoposide, corticosteroids, and methotrexate, although stem cell
transplant is often required.

Answer A is incorrect. Acute lymphoblastic leukemia frequently presents with constitutional
symptoms (fever, weight loss, pallor, hepatosplenomegaly). Bone marrow aspiration would not demonstrate hemophagocytosis.
Answer B is incorrect. Ewing’s sarcoma frequently presents in the second decade of life with constitutional symptoms (fever, weight loss), bone tenderness, and pathologic fractures.
Bone marrow aspiration would not demonstrate hemophagocytosis.
Answer D is incorrect. Neuroblastoma frequently presents with constitutional symptoms
(fever, weight loss, pallor, hepatosplenomegaly).
It is the most common malignancy of infancy. A bone marrow aspirate would not demonstrate hemophagocytosis.
Answer E is incorrect. Wilms’ tumor frequently presents with an asymptomatic flank mass and/or gross hematuria. It is the most common primary renal tumor in children. Bone marrow aspiration would not demonstrate hemophagocytosis.

Explanation
The correct answer is B. This patient died from complications secondary to septic shock. The patient had evidence of early end-organ failure as demonstrated by his decreased urine output. Patients suffering from septic shock can develop diffuse cortical necrosis (shown in the image) of the kidneys, which is believed to result from a combination of hypoperfusion, microangiopathic thrombosis, and infarction; thromboses may be present in the arterioles, capillaries, and glomeruli. The areas of necrosis are generally confi ned to the cortex and, on gross examination, are sharply demarcated
from the rest of the kidney. In cases where the underlying sepsis is quickly treated with fluid
resuscitation and antibiotics, some function of the kidneys may be preserved; otherwise, overwhelming cortical necrosis usually culminates in death.

Answer A is incorrect. Acute pyelonephritis results from hematogenous or ascending infection
of the kidneys. On gross pathologic examination the kidney typically demonstrates patchy areas of abscess formation, but not diffuse, sharply demarcated areas of cortical necrosis as seen in the image.
Answer C is incorrect. Obstructive uropathy results from a blockage distal to the collecting system of the kidneys. On gross pathologic examination the kidney typically demonstrates dilation of the renal pelvis and calyces, but not sharply demarcated areas of cortical necrosis as seen in the image.
Answer D is incorrect. Papillary necrosis can result from infection, analgesic overuse, sickle cell disease, and a number of other conditions. On gross pathologic examination the kidney typically demonstrates yellow-white areas of necrosis limited to the papillae, but not sharply demarcated areas of cortical necrosis as seen in the image.
Answer E is incorrect. Renal infarction results from thromboembolic disease involving the renal
vasculature. On gross pathologic examination the kidney typically demonstrates wedgeshaped
areas of yellow-white infarction extending from the medulla to the cortex, but not diffuse, sharply demarcated areas of cortical necrosis as seen in the image.

Explanation
The correct answer is A. The fi ndings on microscopy indicate a malignant transformation of normal cells. Increased nuclear-to-cytoplasm ratio, open chromatin, and mitotic figures indicate that cells are actively dividing. Given the patient’s history of multiple sexual partners and postcoital bleeding, these cells likely indicate the presence of cervical cancer. Cervical cancer is commonly linked to human papillomavirus infection. The virus can be isolated during cytology through various methods. It is a double-stranded DNA virus.

Answer B is incorrect. Gram-negative diplococci are not associated with cervical cancer.
However, they can be found in gonorrhea cervicitis.
Answer C is incorrect. There are no gram positive cocci associated with cervical cancer.
Answer D is incorrect. There is no singlestranded virus associated with cervical cancer.
Answer E is incorrect. Squamous cells covered with bacteria can be found in bacterial vaginosis,
which causes foul-smelling discharge. There is no known association between bacterial vaginosis
and cervical cancer.

Explanation
The correct answer is A. HNPCC, also known as Lynch’s syndrome, is a rare autosomal dominant
disorder associated with an increased incidence of colorectal cancer. Generally, the syndrome
is associated with mismatch repair. Approximately 70% of people with the syndrome will develop colorectal cancer, typically at 40–45 years of age. Also, there is a high risk of extracolonic cancer, including endometrial, ovarian, urinary tract, small intestinal, stomach, and biliary cancer. As a result, high-risk patients begin annual screening colonoscopies at age 20–25 years, or 10 years before the age of the youngest diagnosed family member. Women >35 years old typically undergo annual
endometrial biopsy due to the high risk of endometrial carcinoma.

Answer B is incorrect. Cholecystitis is secondary to gallstones in 90% of cases. Increased gallstone formation related to HNPCC may be plausible if the patient had undergone resection of the ileum for extracolonic cancer of the small bowel. Gallstones are known to occur in such patients after ileal resection due to disturbed bilirubin metabolism. Moreover, although HNPCC can be associated with biliary cancer, the patient in this case has yet to show signs of HNPCC, and biliary cancer does not
cause cholelithiasis. Thus, the patient presumably has no increased risk of gallstones or cholecystitis.
Answer C is incorrect. Melanin spots of the buccal mucosa and lips can be seen in Peutz-Jeghers syndrome. This syndrome involves multiple polyps of the small bowel, although the large bowel and rectum can be involved. The polyps are generally considered to be nonmalignant hamartomas, but cancer can occasionally develop. Peutz-Jeghers syndrome is not associated with HNPCC.
Answer D is incorrect. Pseudopolyps, also known as infl ammatory polyps, are areas of regenerating,
normal mucosa around which the mucosa has been lost. This typically occurs in the setting of inflammatory bowel disease but may be seen in colitis related to amebic and schistosomal infection or bowel ischemia. Although these “polyps” are not premalignant, they resemble adenomatous polyps on gross examination and should thus be removed and examined histologically. Pseudopolyps are not associated with HNPCC and are unlikely in this patient with no signifi cant past medical history.
Answer E is incorrect. Although vitamin B12 defi ciency is most commonly associated with
pernicious anemia, abdominal surgery secondary to cancer might lead to vitamin B12 deficiency. For example, if the patient underwent gastrectomy for gastric cancer caused by HNPCC, intrinsic factor would not be produced. Furthermore, if the patient underwent bowel resection, including the ileum for small bowel cancer related to HNPCC, B12 could not be absorbed because absorption occurs in
the ileum. However, the patient in this case has yet to show signs of HNPCC and presumably
has normal vitamin B12 levels.

Explanation
The correct answer is D. The patient’s symptoms are consistent with adult polycystic kidney
disease (APKD), a disease most commonly caused by mutation of the polycystin 1 gene located
on chromosome 16. APKD can also be caused by a mutation in polycystin 2 located on chromosome 4, although this is less common. APKD is characterized by the growth of renal cysts, which are believed to lead to renal failure by compressing adjacent normal parenchyma.
The disease often presents in the third or fourth decade of life, and symptoms and signs include abdominal discomfort, frequent urinary tract infections, hematuria, polyuria, and nocturia. Cystic kidneys are often seen on imaging. Mild proteinuria is common. Hepatic cysts, as seen in the image, are also common. The disease is also associated with berry aneurysms and mitral valve prolapse.

Answer A is incorrect. A mutation on chromosome 3 is associated with von Hippel-Lindau disease, which can not only cause renal cysts but also retinal angiomas and central nervous system hemangioblastomas.
Answer B is incorrect. A mutation on chromosome 6 is associated with recessive polycystic
kidney disease, which is associated with a much younger age of onset.
Answer C is incorrect. A mutation on chromosome 9 is associated with tuberous sclerosis,
which can not only cause renal cysts, but also presents with adenoma sebaceum and central
nervous system hamartomas.

Explanation
The correct answer is C. This child most likely has Angelman’s syndrome. Individuals with this phenotype have a characteristic facies with microcephaly, maxillary hypoplasia, deepset eyes, and a large mouth with tongue protrusion. Their gait is jerky and “puppet-like,” and their behavior is marked by frequent paroxysms of inappropriate laughter. Severe mental retardation and speech impairment are usually present, and 80%–90% of patients have epilepsy.
Angelman’s syndrome, along with Prader-Willi syndrome, is a classic example of imprinting, which occurs when the phenotype differs depending on whether the mutation is of paternal or maternal origin. Deletions in Prader-Willi syndrome, a phenotypically distinct disorder, occur exclusively on the paternal chromosome 15, whereas deletions at the same site of chromosome 15 on the maternal
chromosome result in Angelman’s syndrome.
Answer A is incorrect. Anticipation is the phenomenon in which the severity of a disease worsens in succeeding generations. This occurs, for example, in triplet repeat diseases such as Huntington’s disease, wherein the triplet repeat tends to lengthen, age of onset decreases, and disease severity increases with successive generations. This does not occur in Angelman’s syndrome.
Answr B is incorrect. Heteroplasmy describes the presence of both normal and mutated mitochondrial
DNA. This phenomenon is responsible for the variable expression of mitochondrial inherited diseases.
Answer D is incorrect. Locus heterozygosity describes the phenomenon by which mutations at different loci can result in the same phenotype. An example of this is albinism, which can be caused by a number of different mutations.
Answer E is incorrect. Mosaicism occurs when cells in the body have different genetic makeup. This sometimes occurs, for example, in Turner’s syndrome. This does not occur in Angelman’s syndrome.

Explanation
The correct answer is B. Duchenne’s muscular dystrophy (DMD) is the most common form of muscular dystrophy, affecting 1 in 3500 live male births. Symptoms become evident by the age of 5 years and include delayed walking, clumsiness, weakness in the pelvic girdle muscles, and enlargement of the calf muscles (termed pseudohypertrophy). Laboratory testing reveals an elevated creatine kinase level. DMD is caused by an abnormality of Xp21, the region that codes for dystrophin, a myocyte anchoring protein.
Answer A is incorrect. Cystic fi brosis transmembrane conductance regulator (CFTR) transports chloride ions across epithelial cell membranes. Mutations of the CFTR gene lead to cystic fibrosis, which is associated with symptoms such as diffi culty breathing, frequent pneumonias, and pancreatic insufficiency.
Answer C is incorrect. Phenylalanine hydroxylase (PAH) is an enzyme that catalyzes the conversion
of phenylalanine to tyrosine. Deficiency of PAH leads to phenylketonuria, characterized by problems with brain development, mental retardation, and seizures.
Answer D is incorrect. Spectrin is a cytoskeletal protein important in maintaining RBC plasma membrane structure. Absence of spectrin leads to hereditary spherocytosis, whose symptoms include anemia, splenomegaly, and jaundice.
Answer E is incorrect. Type II collagen is the building block of articular and hyaline cartilages.
Defi ciency of type II collagen leads to a severe form of osteogenesis imperfecta that is usually lethal in the perinatal period.

Explanation
The correct answer is A. This patient has developed nasopharyngeal carcinoma, a condition common in certain parts of the world, including Asia and Africa. Development of this tumor is always associated with infection by Epstein-Barr virus (EBV), a DNA virus in the herpesvirus family. Development of this tumor is believed to be related to a synergistic interaction between EBV and a diet high in carcinogenic nitrosamines (common in foods that has been smoked or preserved). Common symptoms include nasal congestion, epistaxis, ear infections (due to tumor-induced blockage of the Eustachian tubes), and headache.
Answer B is incorrect. Many bacteria are capable of infecting the nasopharynx; however, none are directly associated with malignancy.
Answer C is incorrect. Nasopharyngeal zygomycosis is a condition that could present with these symptoms in an immunocompromised patient. However, biopsy would show filamentous nonseptate hyphae and a granulomatous response.
Answer D is incorrect. Although a tuberculoma in the nasopharynx can be confused with a nasopharyngeal tumor, biopsy would show caseating granulomas with multinucleated giant cells.
Answer E is incorrect. Although a retrovirus such as HIV can create an immunocompromised
state favoring the development of a malignancy, it is not the direct cause of tumor formation. Lymphomas can be associated with the retrovirus human T-cell lymphoma virus; however, biopsy would show sheets of malignant T lymphocytes typical of this lymphoma. Other RNA viruses are not associated with malignancy.

Explanation
The correct answer is C. This patient is suffering from squamous cell carcinoma of the bladder.
Although this condition is rare in the United States, it is the most common type of bladder cancer in the world. The most common cause is chronic irritation by the eggs of the helminth Schistosoma haematobium, which lodge in the bladder wall. Squamous cell carcinoma can be distinguished from transitional cell carcinoma pathologically by its appearance. This specimen shows keratin pearl formation, a common fi nding in squamous cell cancers.
Answer A is incorrect. Cigarette smoking is the most common risk factor associated with transitional cell bladder carcinoma. In this case, however, the patient’s presentation and pathology are more suggestive of squamous cell carcinoma.
Answer B is incorrect. Aniline dyes are associated with transitional cell carcinoma, the most common type of bladder cancer in the United States. They are not associated with squamous cell carcinoma of the bladder.
Answer D is incorrect. Papovaviridae such as human papilloma virus are responsible for genital
warts and cervical carcinoma. They are not associated with bladder cancers.
Answer E is incorrect. Long-term catheterization is associated with the development of squamous cell carcinoma of the bladder. Based on the patient’s history, however, there is no reason to assume this patient has had an indwelling catheter at any time.

Explanation
The correct answer is C. The image shows the typical large, round intranuclear inclusion with perinuclear halo seen in cells affected by cytomegalovirus (CMV) infection. This Cowdry type A bodies are typically referred to as “owl’s eyes” due to their microscopic appearance. In immunocompromised patients, CMV infection can present as retinitis, pneumonitis, infl ammation along the gastrointestinal tract, polyradiculopathy, transverse myelitis, and focal encephalitis. In patients with HIV/AIDS, these sequelae occur most prominently when the CD4+ cell count is 10,000 copies/mm3. CMV can cause further immunosuppression, leading to other opportunistic infections such as Pneumocystis and Aspergillus pneumonia.
Answer A is incorrect. Candida is a fungus that produces a wide spectrum of diseases, ranging from superfi cial mucocutaneous disease in immunocompetent hosts to invasive illnesses in immunocompromised hosts. Histology reveals round or ovoid yeast cells, hyphae, or pseudohyphae.
Answer B is incorrect. Cryptococcus neoformans causes meningitis and meningoencephalitis in patients with AIDS. This fungus is difficult to observe with routine hematoxylin and eosin stains, so methenamine silver or periodic acid-Schiff stains are used to identify the characteristic narrow-based buds and round-to-oval yeast, surrounded by a polysaccharide capsule.
Answer D is incorrect. Herpes simplex virus in HIV-infected individuals can cause recurrent orolabial, genital, and perianal lesions. A Tzanck smear is positive for multinucleated epithelial giant cells. It does not cause the large intranuclear inclusion body shown.
Answer E is incorrect. Mycobacterium avium causes lung disease in immunocompromised hosts and is subsequently spread via the blood to the liver, spleen, bone marrow, and other sites. Histology of mycobacterium is not consistent with this image. Rather, acid-fast staining would show organisms in foamy macrophages, granulomas, giant cells, and cells with eosinophilic necrosis.
Answer F is incorrect. Pneumocystis jiroveci (formerly carinii) causes pneumonia in immunocompromised individuals

Explanation
The correct answer is C. Hereditary hemochromatosis is an autosomal recessive adult onset disorder characterized by inappropriately high iron absorption that leads to progressive iron overload. The organs damaged by iron deposition include the liver, heart, pancreas, pituitary, joints, and skin. Cirrhosis results from progressive iron deposition in the liver parenchyma of patients with hemochromatosis. In the image, hepatocellular iron deposition is seen as granular brown cytoplasmic pigment. Microscopic evidence of cirrhosis includes an increased quantity of connective tissue extending from the portal areas. Cirrhosis, which simply means fi brosis, is the result of past or
chronic tissue destruction. Acute destruction would be evidenced by the presence of inflammatory
cells in the portal areas, as is seen in hepatitis.

Answer A is incorrect. Alcoholic liver disease occurs in patients who are heavy drinkers. Liver biopsy in these patients may show cirrhosis. However, in contrast to patients with hemochromatosis, the hepatic iron levels are relatively normal, and iron stores are usually

Explanation
The correct answer is E. This HIV-positive patient has multiple anogenital warts, or condylomata
acuminata, which are commonly caused by human papilloma virus (HPV) types 6 and 11. A feared complication of condylomata acuminata is anorectal cancer, as seen here. Immunodefi ciency predisposes to the development of HPV-induced transformation. The mechanism of HPV-induced transformation involves the production of a viral protein, E6, which binds to a cellular ubiquitin ligase E6AP. On binding to E6, E6AP polyubiquitinates the tumor suppressor p53, leading to dysregulated cell proliferation and, eventually, oncogenesis.

Answer A is incorrect. APC is a tumor suppressor gene mutated in certain hereditary forms of colon cancer. The APC protein normally degrades the transcription factor β-catenin, which is involved in colonic epithelial cell proliferation. In the absence of APC, increased levels of β-catenin accumulate, eventually leading to oncogenesis.
Answer B is incorrect. BRCA1 is a tumor suppressor gene commonly mutated in hereditary forms of breast and ovarian cancers. The BRCA1 protein functions in DNA repair processes, and inherited mutations in BRCA1 interfere with DNA repair, leading to the accumulation of mutations and, eventually, oncogenesis.
Answer C is incorrect. The MSH2 gene regulates a mismatch repair enzyme and is mutated in certain hereditary forms of colon cancer. In the absence of MSH2, increased levels of DNA
mutations accumulate, leading to eventual cellular transformation.

Answer D is incorrect. NF1 is a tumor suppressor gene mutated in neurofi bromatosis type 1. The NF1 protein functions as a GTPase activating protein for the small G protein Ras. Because Ras is only active when it is GTPbound, NF1-mediated GTP hydrolysis leads to inactivation of Ras. In the absence of NF1, Ras is hyperactive, leading to enhanced growth factor signal transduction and, eventually, oncogenesis.

Explanation
The correct answer is A. The boy’s brain biopsy demonstrates medulloblastoma. This is a poorly differentiated neuroectodermal tumor that occurs predominantly in children and exclusively in the cerebellum. The cerebellar vermis is the medial section of the cerebellum and is responsible for proximal muscle coordination, balance, and vestibulo-ocular refl exes. As seen in this patient, lesions of the vermis lead to vertigo, nausea, and diffi culties in coordinating movement of trunk and proximal limb muscles. The presence of medulloblastoma commonly leads to obstruction of the outflow of cerebrospinal fluid and the potential for hydrocephalus, a life-threatening condition.

Answer B is incorrect. Medulloblastomas arise in the midline of the cerebellum in children. The intermediate section of the cerebellar hemisphere is more lateral than the vermis. Lesions in the intermediate section would cause deficits in coordinating movements of the ipsilateral distal extremities, not the vertigo and proximal limb problems seen in this patient.

Answer C is incorrect. Medulloblastomas arise in the midline of the cerebellum in children. Lesions of the lateral hemisphere would likely cause defi cits in planning movements of the ipsilateral distal extremities, not the vertigo and proximal limb problems seen in this patient.

Answer D is incorrect. Medulloblastomas arise in the midline of the cerebellum in children, not in the occipital cortex. Occipital cortex lesions could lead to defects in vision, not the vertigo and proximal limb problems seen in this patient.

Answer E is incorrect. Medulloblastomas arise in the midline of the cerebellum in children, not in the parietal cortex. The postcentral gyrus of the parietal lobe is the primary somatosensory cortex. Lesions of this area would cause sensory defi cits, not the vertigo and proximal limb problems seen in this patient.

Explanation
The correct answer is B. This image demonstrates an advanced case of mesothelioma, in which the entire left lung is encased with tumor. The clinical history supports this diagnosis. Asbestos is present in certain building materials and fi re-resistant materials, and exposure to asbestos is a risk factor for the development of mesothelioma.

Answer A is incorrect. Afl atoxin B is produced by Aspergillus and is a common contaminant of cereals, spices, and nuts. It has been associated with carcinoma of the liver.

Answer C is incorrect. Long-term exposure to high levels of benzene can lead to leukemia and Hodgkin’s lymphoma. Benzene is the main component of light oil, and is found in gasoline and other fuels.

Answer D is incorrect. Cadmium is a carcinogen associated with the development of prostate
cancer. It can be found in batteries and in metal coatings.

Answer E is incorrect. Exposure to silica may occur in the manufacturing of several materials,
such as glass, ceramics, and electronics. Silicosis is characterized by bilateral, fi ne nodularity in
the upper lung lobes. It is slowly progressive. Its role as a carcinogen is controversial.

Explanation
The correct answer is E. This patient is in shock due to cardiac tamponade secondary to the rupture of the ventricular free wall, which usually occurs 4–10 days after the initial myocardial infarction (MI). It usually presents with sudden shock with signs of cardiac tamponade, such as the hypotension, distant heart sounds, and elevated jugular venous pressure observed in this patient. Survival depends primarily on the rapid recognition of myocardial rupture and the provision of immediate therapy, such as urgent pericardiocentesis or surgery. Unfortunately, this complication of an MI is often a fatal one.
Answer A is incorrect. Aneurysm formation may occur post-MI due to a lack of contractility that results in the infarcted area. Sequelae of ventricular aneurysm formation include decreased cardiac output, increased risk of arrhythmias, and potential mural thrombus formation with risk of mbolization.
Answer B is incorrect. Cardiac arrhythmias are a common cause of death in the first few days after an MI. However, this patient’s clinical picture is more consistent with a diagnosis of cardiac tamponade secondary to ventricular free wall rupture.

Answer C is incorrect. Fibrinous pericarditis is a complication that usually occurs 3–5 days post-MI. This condition usually presents with chest pain that is relieved when the patient leans forward; often a pericardial friction rub can be auscultated on cardiac examination. However, this patient’s clinical picture is more consistent with a diagnosis of cardiac tamponade secondary to ventricular free wall rupture.
Answer D is incorrect. Papillary muscle rupture is another complication of MI that usually occurs 4–10 days post-MI. However, patients with papillary muscle rupture usually present with acute mitral regurgitation, causing the abrupt onset of heart failure in the setting of a new systolic murmur. Emergent surgical intervention is the treatment of choice for this condition.