USMLE-STEP-3 Exam Questions & Answers

Correct Answer: C Section: (none)

Explanation:

The patient's most likely diagnosis is superior vena cava syndrome (SVCS), which is usually due to external compression of the SVC by tumor or lymph nodes, sometimes associated with intraluminal thrombosis. The diagnosis is established by CT of the chest with intravenous contrast, which can demonstrate the level and extent of obstruction, as well as the presence of any caval thrombus. Plain chest radiography may show some mediastinal widening, but yields much less information. Echocardiography would be appropriate if the patient had suspected pericardial effusion with tamponade, but that would not produce unilateral arm edema and discoloration. Doppler studies of the deep veins of the arm would be useful if the problem were isolated to the upper extremity. In this case, the cerebral venous drainage is also involved, so the obstruction is more proximal, i.e. at the level of the SVC. Arteriogram would not be indicated, since the issue in this case is venous obstruction, not arterial insufficiency. Unless the patient has cerebral edema with mental status changes or upper airway compromise due to tracheal obstruction, the diagnosis of SVCS is not immediately life-threatening, and emergent therapy is not usually indicated. The majority of patients with SVCS present with this as the initial presentation of their malignancy, before a tissue diagnosis has been established. This is problematic, since therapy is guided by the underlying malignancy (radiation therapy for non-small cell lung cancers, chemotherapy +/-radiation for small cell lung cancers or lymphomas), but empiric initiation of radiation or glucorticoids (if the underlying diagnosis is lymphoma) may obscure the histologic diagnosis. The most important initial step is to try to obtain a biopsy to establish the cancer type before initiating therapy. If symptoms are severe, placement of intravascular stents may provide rapid symptomatic relief without compromising subsequent diagnostic or therapeutic efforts. Surgical intervention is rarely indicated, and usually only for benign causes of SVCS.

Correct Answer: D Section: (none)

Explanation:

This patient presents with classic symptoms of a bowel obstruction. The diagnosis is often made by a thorough history and physical examination. Following the initial evaluation, an acute abdominal x-ray series should be obtained, which includes supine and erect views of the abdomen. The diagnosis is confirmed with the presence of dilated loops of bowel with the presence of air-fluid levels. These plain films may also suggest the location of the obstruction (small vs. large intestine). Abdominal ultrasonography has limited role in the diagnosis or management of intestinal obstruction. Serum electrolyte determination helps in identifying the electrolyte disturbances that have taken place. Fluid loss needs to be corrected with rehydration, and nasogastric suction helps in decreasing abdominal distention. Upper GI endoscopy would increase distention, and is contraindicated. Antiemetics should not be given until a definitive diagnosis is made, and then only if indicated; promotility agents have little to no role in the management of a patient with bowel obstruction, and may even be contraindicated.

An annular constricting lesion with overhanging edges is typical of annular carcinoma of the colon. Mechanical small bowel obstruction results in multiple air-fluid levels in distended small bowel loops. Intussusception produces a "corkscrew" appearance on barium enema, and sigmoid volvulus produces a "bird's beak" appearance. In diverticulitis, extravasation of barium outside the lumen of the colon typically is seen.

Correct Answer: C Section: (none)

Explanation: The current American College of Obstetricians and Gynecologists guidelines for screening women on tamoxifen for endometrial cancer state that no screening except for routine yearly gynecologic examinations should be performed in asymptomatic women. In symptomatic women with vaginal bleeding on tamoxifen therapy, endometrial biopsy is recommended. Tamoxifen directly affects the endometrium, and a pelvic ultrasound will reveal a thickened endometrium in 75% of asymptomatic women. The most common changes to the endometrium include benign cystic glandular dilation, stromal edema, endometrial hyperplasia, and polyps. Approximately 2030% of women will develop benign endometrial and endocervical polyps. Women on tamoxifen have a two-to threefold increased risk for endometrial cancer. Given the high rate of benign changes in the endometrium from tamoxifen, the usefulness of TVUS and endometrial biopsy is drastically diminished. In the setting of tamoxifen, ultrasound has only a 9% positive predictive value. However, the negative predictive value is 99%, meaning that if the ultrasound is normal, you may be 99% certain that there is no disease present. CT scans in general are less effective than ultrasound at evaluating the endometrial cavity, and they are not recommended for screening. Hysteroscopy will allow direct visualization with directed biopsy of the abnormal endometrium. However, again, the majority of lesions in women on tamoxifen will be benign, and a large number of hysteroscopies would be performed with the detection of very few cancers. Thus, this is not cost-effective and is a low yield diagnostic procedure in this group of women. Also, there is some debate as to whether hysteroscopy in the presence of endometrial cancer increases the risk for positive cytology and leads to a seeding of the peritoneal cavity with endometrial cancer cells by efflusing cancer cells from the endometrium out through the Fallopian tubes into the abdominal cavity.