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  1. 1. 28th Annual In-Training Examination for Diagnostic Radiology Residents Rationales Sponsored by: Commission on Education Committee on Residency Training in Diagnostic Radiology February 3, 2005 The American College of Radiology www.acr.org
  2. 2. Section XII – Nuclear Figure 1 320. You are shown coronal images from an F-18 FDG PET study (Figure 1) performed in a 62-year-old man with a history of alcohol abuse, presenting with abdominal pain. What is the MOST likely diagnosis? A. Hodgkin’s disease B. Metastatic colon carcinoma C. Hepatocellular carcinoma D. Pancreatic carcinoma American College of Radiology
  3. 3. Section XII – Nuclear Question #320 Findings: Coronal FDG-PET images demonstrate a focal area of markedly increased tracer uptake in the right lower quadrant, in the region of the cecum. There are multiple focal right iliac and paraaortic lymph node metastases and numerous focal hypermetabolic lesions in the liver, consistent with hepatic metastases. Rationales: A. Incorrect. Hodgkin’s disease is usually highly FDG-avid, and commonly involves abdominal and pelvic lymph nodes and the liver. However, the more discrete focal lesion in the right lower quadrant is more typical for a primary lesion within the right colon. In addition, there is no splenomegaly or other sites of lymphadenopathy, which would commonly be seen in association with involvement of the liver and abdominal and pelvic nodes. Extensive involvement of the liver is also more common in non-Hodgkin’s lymphoma. Therefore, while Hodgkin’s disease is a plausible diagnosis, metastatic colon carcinoma is more likely in this case. B. Correct. The findings in this case are typical for advanced carcinoma of the cecum, with increased FDG uptake noted in the primary lesion, regional lymph nodes, and extensive hepatic metastases visualized. FDG-PET imaging is highly sensitive for the staging and re-staging of colon carcinoma, and is substantially more sensitive and specific than CT for this purpose. C. Incorrect. Hepatocellular carcinoma demonstrates variable FDG uptake on PET scans. It can be solitary or multifocal. However, it would be unusual to see lymph node metastases remote from the liver, and the larger focal lesion in the right lower quadrant would not constitute a typical site of metastatic involvement. D. Incorrect. FDG uptake of pancreatic carcinoma is also variable. Multiple hypermetabolic hepatic metastases may occur, and can have the appearance seen in this case. However, adenopathy in the pelvis would be uncommon, and there is also no evidence of increased FDG uptake within a primary lesion in the pancreas. The small foci of increased uptake in the lower epigastric region could conceivably be located within the body of the pancreas, but are not striking, and are relatively inferiorly located. These foci are more consistent with small paraaortic lymph node metastases. Citations: Lowe VJ, Delbeke D, Coleman RE. Applications of PET in oncologic imaging. In: Sandler MP, et al, eds. Diagnostic Nuclear Medicine. 4th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2003:987-1014. Bar-Shalom R, Valdivia AY, Blaufox MD. PET imaging in oncology. Semin Nucl Med. 2000; 30:150-185. Hustinx R, Benard F, Alavi A: Whole-body FDG-PET imaging in the management of patients with cancer. Semin Nucl Med. 2002;32:35-46. Diagnostic In-Training Exam 2005
  4. 4. Section XII – Nuclear Figure 2 321. You are shown a posterior Tc-99m MDP bone scintigram (Figure 2) obtained in a 58-year-old man with back pain. What is the MOST likely diagnosis? A. Metastatic prostate carcinoma B. Acute osteomyelitis C. Metastatic renal carcinoma D. Prior radiation therapy American College of Radiology
  5. 5. Section XII – Nuclear Question #321 Findings: Whole-body and spot images of the skeleton demonstrate a focal area of decreased tracer uptake within the vertebral body of T12. The remainder of the study demonstrates only mild arthritic changes. The focal “hot spot” in the region of the left elbow is related to a small amount of extravasation of the dose at the site of injection. Rationales: A. Incorrect. Prostate carcinoma has a high predilection for metastasis to the skeleton, and bone scintigraphy is a highly sensitive examination for detection of prostate carcinoma metastatic to bone. Prostate carcinoma often metastasizes early to the thoracolumbar spine via the vertebral venous plexus of Batson. However, in the vast majority of cases, prostate carcinoma bone metastases demonstrate increased tracer uptake on Tc-99m MDP or Tc-99m HDP bone scans. Radiographically, prostatic carcinoma bone metastases are often associated with sclerotic lesions on plain films or CT. In this case, the lesion demonstrates decreased tracer uptake, a relatively uncommon finding that is more often associated with aggressive, lytic destructive lesions or metastases from primary lesions less likely to result in blastic or bone-forming lesions, such as renal and thyroid carcinoma. Statistically, “cold” bone metastases are most often due to metastatic lung or breast carcinoma. Therefore, while plausible, metastatic prostate carcinoma is not the most likely etiology for the findings in this case. B. Incorrect. Acute osteomyelitis is most often associated with focal skeletal hyperemia on the flow portion of 3-phase bone scans and with focal increased bone uptake on the blood pool and delayed static images. In children, acute osteomyelitis is occasionally associated with decreased tracer uptake on bone scintigraphy secondary to decreased perfusion to involved sites due to the presence of pus under pressure within the involved bone. However, this appearance is much less commonly encountered in adult patients, and when it occurs, it is primarily encountered in the long bones. Therefore, osteomyelitis would be an unlikely explanation for the finding in this case. In addition, no history suggesting the presence of an infectious process was given. C. Correct. Renal carcinoma is one of the primary neoplasms that may be associated with well-circumscribed, expansile lytic metastases on radiographs and “photopenic” skeletal metastases on bone scintigrams, along with thyroid carcinoma. As noted above, statistically the most common primary neoplasms associated with “cold” metastases are lung and breast carcinoma. “Cold” lesions or absence of abnormal tracer uptake may also be seen in multiple myeloma, a lesion arising within the bone marrow, for which plain radiographs are overall more sensitive than skeletal scintigraphy for detection. Only a small percentage of metastases detected on bone scintigraphy are “cold” lesions, like the lesion in this case. D. Incorrect. Radiation therapy can produce decreased tracer uptake on bone scintigrams secondary to reduction in regional blood flow and microvascular injury and injury to osteoblasts, with resultant decreased new bone formation. However, it would be unusual for a radiation therapy port to involve only a single vertebral level. In addition, in the current case the entire vertebra is not involved, with activity remaining in portions of the posterior elements, which would not be anticipated in the case of postradiation changes. Therefore, radiation therapy is not the most likely etiology for the finding in this case. Citations: Alazraki NP: Case 1: “Cold” Bone Metastasis. In: Siegel BA, ed. Nuclear Radiology II. Chicago, Ill: American College of Radiology; 1978:2-17. Diagnostic In-Training Exam 2005
  6. 6. Section XII – Nuclear Figure 3 322. You are shown anterior whole body Tc-99m MDP bone scan (Figure 3) in a 84-year-old woman with head and neck pain and a history of papillary thyroid carcinoma. What is the MOST likely explanation for the scintigraphic findings? A. Poor bone uptake due to osteoporosis B. Metastatic calcification due to hyperparathyroidism C. Poor labeling of the MDP D. Metastatic papillary thyroid cancer American College of Radiology
  7. 7. Section XII – Nuclear Question #322 Findings: There is marked increased activity in the stomach, thyroid, and salivary glands, with some activity seen in bowel and bladder. Rationales: A. Incorrect. Patients with severe osteoporosis may demonstrate relatively decreased activity in the skeletal system, with increased soft tissue activity. Diffusely increased skeletal uptake may also occur. However, osteoporosis would not show localization in the sites mentioned above. B. Incorrect. Metastatic calcifications can result in increased activity in the stomach, lungs, kidneys, and other soft tissue locations. However, it would not demonstrate increased activity in salivary glands or thyroid. C. Correct. Free Technetium-99m pertechnetate, which occurs when there is poor labeling of the MDP, will localize in the locations mentioned above, the stomach, thyroid, and salivary glands. This condition can be confirmed by performing thin-layer paper chromatography on the radiopharmaceutical. D. Incorrect. Metastatic papillary thyroid cancer may show areas of increased or decreased activity in the skeleton on a bone scan. Soft tissue metastases in the thyroid bed, cervical lymph nodes, lungs or mediastinum may be seen on a whole body I-131 or I-123 scan, but are not normally visualized on a bone scan. Thus, metastatic papillary thyroid carcinoma would not demonstrate the distribution of radiotracer seen above. Diagnostic In-Training Exam 2005
  8. 8. Section XII – Nuclear Figure 4 323. A 54-year-old diabetic man presents 5 days following renal transplantation with pain at the graft site. You are shown anterior Tc-99m MAG-3 scintigraphic images of the pelvis (Figure 4). What is the MOST likely diagnosis? A. Urinoma B. Acute tubular necrosis C. Lymphocele D. Acute rejection American College of Radiology
  9. 9. Section XII – Nuclear Question #323 Findings: There is prompt perfusion to the transplanted kidney in the right iliac fossa, with normal tubular transit time and prompt excretion into the collecting system and bladder. In addition, there is progressive accumulation of activity in the right lower quadrant appearing during the excretory phase of the study. Rationales: A. Correct. An often-painful surgical complication, urinary extravasation (urinoma) is demonstrated by progressive accumulation of tracer, which persists postvoiding. The current case findings are diagnostic of a urinoma. B. Incorrect. Acute tubular necrosis (ATN), though common, is typically painless. ATN is associated with relatively preserved perfusion to the transplant with poor tubular function, without extrarenal tracer accumulation. The findings in this case are not consistent with ATN. C. Incorrect. A common postsurgical complication, lymphoceles typically produce photopenic fluid collections adjacent to the transplant, since they are not in communication with the renal collecting system. In addition, lymphoceles are a later complication, not usually occurring during the first postoperative week. D. Incorrect. Acute rejection is occasionally painful, and is associated with poor flow and function of the graft, manifested by delayed and reduced uptake and excretion by the transplanted kidney. Neither finding is present in this case. In addition, the progressive accumulation of activity in the right lower quadrant, surrounding the transplant, cannot be explained by acute rejection. Citations: Dubovsky E. Evaluation of renal transplants. In: Henkin R, et al, ed. Nuclear Medicine. St Louis, Mo: Mosby; 1996. Diagnostic In-Training Exam 2005
  10. 10. Section XII – Nuclear Figure 5 324. You are shown stress and rest vertical long-axis images (Figure 5) from a SPECT myocardial perfusion scan in a 50-year-old woman with chest discomfort. During treadmill exercise, the patient achieved 70% of the maximum predicted heart rate. What is the MOST likely explanation of the findings? A. Normal study B. Diaphragmatic attenuation artifact C. Inferior wall ischemia D. Non-diagnostic study due to inadequate heart rate response American College of Radiology
  11. 11. Section XII – Nuclear Question #324 Findings: There is a moderate area of mildly decreased perfusion in the inferior wall, with reversibility noted on the resting study. Rationales: A. Incorrect. There is a moderate reversible defect of mild severity noted in the inferior wall. This is not a normal study. B. Incorrect. Diaphragmatic attenuation can produce artifactual defects in the inferior wall region. Typically, diaphragmatic attenuation affects both the stress and resting studies, producing fixed defects, unless there is significant patient motion between the two sets of images. Diaphragmatic attenuation is more commonly seen in male patients. Therefore, while plausible, diaphragmatic attenuation artifact is not the most likely diagnosis in this case. C. Correct. The best explanation for the findings in this case is exercise-induced ischemia involving the inferior wall, corresponding to the right coronary artery territory. D. Incorrect. The patient achieved only 70% of maximum predicted heart rate during treadmill exercise. The usual target for exercise studies is 85% of maximum predicted heart rate (based on maximum predicted heart rate = 220 – age). A submaximal exercise test reduces the sensitivity of the study. However, if the patient demonstrates ischemia despite failure to achieve the target heart rate, then the findings are still valid, although it should be noted that the degree or extent of exercise-induced ischemia may be underestimated. Diagnostic In-Training Exam 2005
  12. 12. Section XII – Nuclear 325. What factor is MOST important in identifying sentinel lymph nodes on breast lymphoscintigraphy studies? A. Nodal size B. Proximity to the injection site C. Intensity of uptake D. Timing of visualization Question #325 Rationales: A. Incorrect. Nodal size is not a factor considered in identifying sentinel lymph nodes. The sentinel node(s) may or may not be the largest ones visualized, but are correctly identified as being the first node(s) visualized. B. Incorrect. The sentinel node(s) are often located close to the site of injection, and are usually closer to the injection site than other visualized nodes. However, as a result of the variability of lymphatic pathways, it is possible for the sentinel node to be located farther from the site of injection than other nodes that visualize later. C. Incorrect. The sentinel node may or may not be the “hottest” node seen on imaging. This factor is irrelevant in the identification of the sentinel node(s). D. Correct. The essential element in the identification of the sentinel node(s), whether single or multiple, is the fact that they are visualized prior to any other nodes seen. Citations: Glass EC, Essner R, Giuliano AE. Sentinel node localization in breast cancer. Semin Nucl Med. 1999; 29:57-68. American College of Radiology
  13. 13. Section XII – Nuclear 326. The likelihood of malignancy in a hypofunctioning (“cold”) thyroid nodule identified on I-123 thyroid scintigraphy is increased by ALL of the following EXCEPT: A. Female gender B. Age < 30 years old C. Prior head and neck irradiation D. Absence of other thyroid nodules Question #326 Rationales: A. Correct. The overall incidence of thyroid carcinoma is greater in females than males. However, the incidence of benign thyroid nodular disease is substantially greater in females than in males. As a result, in a given patient with a solitary thyroid nodule, the risk of malignancy is relatively greater in males, and female gender is therefore not a relative risk factor. B. Incorrect. The incidence of thyroid carcinoma increases overall with increasing age, with a bimodal distribution. However, the incidence of benign thyroid nodules increases more rapidly with increasing age, therefore the relative risk of malignancy is greater in younger patients. C. Incorrect. The incidence of thyroid carcinoma is increased 3- to 4-fold in patients exposed to radiation than the general public. In particular, more than 1 million patients were given hundreds of rads of radiation to the head and neck region for the treatment of benign pediatric conditions such as acne, tonsillitis, and thymic enlargement, before the risks of this exposure were widely known. This practice was commonplace during the period from 1940-1960, and some of these patients are still being monitored for the development of thyroid cancer. The distribution of lesions in these patients is not significantly different than that encountered in spontaneously occurring thyroid carcinoma. The incidence of benign thyroid nodules is also significantly increased in this patient population. By contrast, the much higher radiation exposure to the thyroid gland that occurs with radioiodine treatment for Graves’ disease, in the order of tens of thousands of rads, is not associated with an increased risk of thyroid carcinoma. D. Incorrect. The likelihood of malignancy in a cold nodule is substantially greater if the lesion is either solitary or a dominant lesion, ie, one that is substantially larger than any other focal thyroid nodule present. On the other hand, the incidence of thyroid carcinoma in patients with multinodular goiters is only in the range of 5%, provided that they were not previously exposed to head and neck irradiation. Citations: Martin WH, Sandler MP. Thyroid imaging. In: Sandler MP, et al, eds. Diagnostic Nuclear Medicine. 4th Philadelphia, Pa: Lippincott Williams & Wilkins; 2003:616-625. Diagnostic In-Training Exam 2005
  14. 14. Section XII – Nuclear 327. ALL of the following are associated ventilation-perfusion mismatch EXCEPT: A. Hypoplastic pulmonary artery B. Chronic pulmonary embolism C. Mucus plugging D. Radiation therapy Question #327 Rationales: A. Incorrect. Hypoplastic pulmonary arteries are often associated with a degree of ventilation-perfusion mismatch. B. Incorrect. Chronic pulmonary embolism will demonstrate ventilation-perfusion mismatches. C. Correct. Mucus plugging is a primary ventilatory disorder, and most commonly demonstrates matching ventilation and perfusion abnormalities, secondary to reflex vasoconstriction. D. Incorrect. Radiation therapy to the lungs may produce ventilation-perfusion mismatches in the areas irradiated, corresponding to the geometry of the radiation port. American College of Radiology
  15. 15. Section XII – Nuclear 328. Aluminum ion (Al3+) breakthrough following elution of a Molybdenum-99/Tc-99m generator is: A. Physically harmful to the patient B. Detectable colorimetrically C. Detectable with a dose calibrator D. A radiochemical impurity Question #328 Rationales: A. Incorrect. Although a heavy metal, the chemical quantity is inadequate to cause direct physical harm to a patient. Aluminum impurities are only indirectly harmful by their unexpected chemical interaction with various radiopharmaceutical preparations, with resultant colloid formation and subsequent altered biodistribution of the radiopharmaceutical, including increased hepatic or pulmonary localization. B. Correct. Qualitative colorimetric analysis of generator eluate placed upon a special test paper chemically sensitive to Al3+ ion is mandated. Excessive amounts of aluminum ion capable of disturbing radiopharmaceutical purity and scan quality will produce an obvious pink color change on the test paper. For a fission-produced generator, the maximum allowable limit for alumina breakthrough is 10 ug/ml of eluate. C. Incorrect. Generator parent Molybdenum-99 breakthrough, a radionuclide impurity, increases the patient radiation dose and also degrades image quality by its high-energy gamma rays (primarily 740 keV) as a result of beta decay, detectable in the dose calibrator. Aluminum 3+ ion is not radioactive, and thus not detectable with a radiation detector device. D. Incorrect. Aluminum ion is a nonradioactive (stable) ionic contamination of a generator eluate, ie, a chemical impurity. Hydrolyzed reduced technetium and free pertechnetate are examples of radiochemical impurities. Citations: Henkin et al. ED. Nuclear Medicine. Vol. I, Chapter 33. Quality control in the hot lab. S. Karesh, Mosby, 1996. Diagnostic In-Training Exam 2005
  16. 16. Section XII – Nuclear 329. Concerning Tc-99m sestamibi uptake, ALL of the following are true EXCEPT: A. The mechanism of uptake is identical to that of Tl-201 chloride. B. Uptake does not directly involve the sodium-potassium ATPase pump. C. It distributes preferentially into tissues with high mitochondrial content. D. Its retention is related to membrane potential. Question #329 Rationales: A. Correct. The mechanism of Tc-99m sestamibi uptake is different than Tl-201. Sestamibi uptake relates to negative plasma membrane potential and cellular mitochondrial content. Therefore, this statement is false, and is the correct answer to this question. B. Incorrect. Tc-99m sestamibi uptake does not directly involve the sodium potassium ATPase pump. By contrast, the uptake of T1-201, a potassium analog, does directly involve the sodium-potassium ATPase pump. C. Incorrect. Tc-99m sestamibi distributes into tissues with relatively high mitochondrial content. The presence of a negative plasma membrane potential and high mitochondrial content are thought to explain the normal uptake in such organs as the heart, liver, kidney, and skeletal muscle. D. Incorrect. Tc-99m sestamibi retention is related to membrane potential. American College of Radiology