23204973

28th Annual

In-Training Examinationfor DiagnosticRadiology ResidentsRationalesSponsored by:Commission on EducationCommittee on Residency Training in Diagnostic Radiology

February 3, 2005

The American College of Radiology www.acr.org

American College of Radiology

Section XII – Nuclear

320. You are shown coronal images from an F-18 FDG PET study (Figure 1) performed in a 62-year-oldman with a history of alcohol abuse, presenting with abdominal pain. What is the MOST likelydiagnosis?

A. Hodgkin’s disease

B. Metastatic colon carcinoma

C. Hepatocellular carcinoma

D. Pancreatic carcinoma

Figure 1

Diagnostic In-Training Exam 2005


Question #320

Findings:Coronal FDG-PET images demonstrate a focal area of markedly increased tracer uptake in the right lowerquadrant, in the region of the cecum. There are multiple focal right iliac and paraaortic lymph node metastasesand 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 lesionwithin the right colon.

In addition, there is no splenomegaly or other sites of lymphadenopathy, which would commonly be seenin association with involvement of the liver and abdominal and pelvic nodes. Extensive involvement of theliver is also more common in non-Hodgkin’s lymphoma.

Therefore, while Hodgkin’s disease is a plausible diagnosis, metastatic colon carcinoma is more likely inthis case.

B. Correct. The findings in this case are typical for advanced carcinoma of the cecum, with increased FDGuptake 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 issubstantially 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 focallesion 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 metastasesmay 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 FDGuptake within a primary lesion in the pancreas.

The small foci of increased uptake in the lower epigastric region could conceivably be located within thebody 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.



321. You are shown a posterior Tc-99m MDP bone scintigram (Figure 2) obtained in a 58-year-old manwith back pain. What is the MOST likely diagnosis?

A. Metastatic prostate carcinoma

B. Acute osteomyelitis

C. Metastatic renal carcinoma

D. Prior radiation therapy

Figure 2



Question #321

Findings:Whole-body and spot images of the skeleton demonstrate a focal area of decreased tracer uptake within thevertebral body of T12. The remainder of the study demonstrates only mild arthritic changes. The focal “hotspot” in the region of the left elbow is related to a small amount of extravasation of the dose at the site ofinjection.

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 carcinomaoften 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 onTc-99m MDP or Tc-99m HDP bone scans. Radiographically, prostatic carcinoma bone metastases areoften associated with sclerotic lesions on plain films or CT. In this case, the lesion demonstrates decreasedtracer uptake, a relatively uncommon finding that is more often associated with aggressive, lytic destructivelesions or metastases from primary lesions less likely to result in blastic or bone-forming lesions, such asrenal and thyroid carcinoma. Statistically, “cold” bone metastases are most often due to metastatic lung orbreast carcinoma. Therefore, while plausible, metastatic prostate carcinoma is not the most likely etiologyfor the findings in this case.

B. Incorrect. Acute osteomyelitis is most often associated with focal skeletal hyperemia on the flow portionof 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 scintigraphysecondary to decreased perfusion to involved sites due to the presence of pus under pressure within theinvolved bone. However, this appearance is much less commonly encountered in adult patients, and whenit occurs, it is primarily encountered in the long bones. Therefore, osteomyelitis would be an unlikelyexplanation for the finding in this case. In addition, no history suggesting the presence of an infectiousprocess 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, alongwith 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 mayalso be seen in multiple myeloma, a lesion arising within the bone marrow, for which plain radiographs areoverall more sensitive than skeletal scintigraphy for detection. Only a small percentage of metastasesdetected 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 toreduction in regional blood flow and microvascular injury and injury to osteoblasts, with resultant decreasednew bone formation. However, it would be unusual for a radiation therapy port to involve only a singlevertebral level. In addition, in the current case the entire vertebra is not involved, with activity remainingin 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.



Figure 3

322. You are shown anterior whole body Tc-99m MDP bone scan (Figure 3) in a 84-year-old womanwith head and neck pain and a history of papillary thyroid carcinoma. What is the MOST likelyexplanation 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



Question #322

Findings:There is marked increased activity in the stomach, thyroid, and salivary glands, with some activity seen in boweland 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 othersoft 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, willlocalize in the locations mentioned above, the stomach, thyroid, and salivary glands. This condition canbe 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 skeletonon a bone scan. Soft tissue metastases in the thyroid bed, cervical lymph nodes, lungs or mediastinum maybe 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.



Figure 4

323. A 54-year-old diabetic man presents 5 days following renal transplantation with pain at the graftsite. You are shown anterior Tc-99m MAG-3 scintigraphic images of the pelvis (Figure 4). What isthe MOST likely diagnosis?

A. Urinoma

B. Acute tubular necrosis

C. Lymphocele

D. Acute rejection



Question #323

Findings:There is prompt perfusion to the transplanted kidney in the right iliac fossa, with normal tubular transit timeand prompt excretion into the collecting system and bladder. In addition, there is progressive accumulation ofactivity 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 diagnosticof a urinoma.

B. Incorrect. Acute tubular necrosis (ATN), though common, is typically painless. ATN is associated withrelatively preserved perfusion to the transplant with poor tubular function, without extrarenal traceraccumulation. The findings in this case are not consistent with ATN.

C. Incorrect. A common postsurgical complication, lymphoceles typically produce photopenic fluid collectionsadjacent to the transplant, since they are not in communication with the renal collecting system. Inaddition, 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 rightlower 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.



Figure 5

324. You are shown stress and rest vertical long-axis images (Figure 5) from a SPECT myocardialperfusion scan in a 50-year-old woman with chest discomfort. During treadmill exercise, the patientachieved 70% of the maximum predicted heart rate. What is the MOST likely explanation of thefindings?

A. Normal study

B. Diaphragmatic attenuation artifact

C. Inferior wall ischemia

D. Non-diagnostic study due to inadequate heart rate response



Question #324

Findings:There is a moderate area of mildly decreased perfusion in the inferior wall, with reversibility noted on theresting 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 thereis 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 theinferior wall, corresponding to the right coronary artery territory.

D. Incorrect. The patient achieved only 70% of maximum predicted heart rate during treadmill exercise. Theusual target for exercise studies is 85% of maximum predicted heart rate (based on maximum predictedheart rate = 220 – age). A submaximal exercise test reduces the sensitivity of the study. However, if thepatient 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.



325. What factor is MOST important in identifying sentinel lymph nodes on breast lymphoscintigraphystudies?

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 thefirst node(s) visualized.

B. Incorrect. The sentinel node(s) are often located close to the site of injection, and are usually closer to theinjection site than other visualized nodes. However, as a result of the variability of lymphatic pathways, it ispossible for the sentinel node to be located farther from the site of injection than other nodes that visualizelater.

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, isthe 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.



326. The likelihood of malignancy in a hypofunctioning (“cold”) thyroid nodule identified on I-123thyroid 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, andfemale gender is therefore not a relative risk factor.

B. Incorrect. The incidence of thyroid carcinoma increases overall with increasing age, with a bimodaldistribution. 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 radiationthan the general public. In particular, more than 1 million patients were given hundreds of rads ofradiation 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 wascommonplace during the period from 1940-1960, and some of these patients are still being monitored forthe development of thyroid cancer. The distribution of lesions in these patients is not significantly differentthan that encountered in spontaneously occurring thyroid carcinoma. The incidence of benign thyroidnodules is also significantly increased in this patient population. By contrast, the much higher radiationexposure to the thyroid gland that occurs with radioiodine treatment for Graves’ disease, in the order oftens 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 eithersolitary or a dominant lesion, ie, one that is substantially larger than any other focal thyroid nodulepresent. On the other hand, the incidence of thyroid carcinoma in patients with multinodular goiters isonly 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.



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 matchingventilation and perfusion abnormalities, secondary to reflex vasoconstriction.

D. Incorrect. Radiation therapy to the lungs may produce ventilation-perfusion mismatches in the areasirradiated, corresponding to the geometry of the radiation port.



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 interactionwith various radiopharmaceutical preparations, with resultant colloid formation and subsequent alteredbiodistribution of the radiopharmaceutical, including increased hepatic or pulmonary localization.

B. Correct. Qualitative colorimetric analysis of generator eluate placed upon a special test paperchemically sensitive to Al3+ ion is mandated. Excessive amounts of aluminum ion capable of disturbingradiopharmaceutical 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 ofeluate.

C. Incorrect. Generator parent Molybdenum-99 breakthrough, a radionuclide impurity, increases the patientradiation dose and also degrades image quality by its high-energy gamma rays (primarily 740 keV) as aresult 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, achemical impurity. Hydrolyzed reduced technetium and free pertechnetate are examples of radiochemicalimpurities.

Citations:Henkin et al. ED. Nuclear Medicine. Vol. I, Chapter 33. Quality control in the hot lab. S. Karesh, Mosby, 1996.



Question #329

Rationales:

A. Correct. The mechanism of Tc-99m sestamibi uptake is different than Tl-201. Sestamibi uptake relates tonegative 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. Bycontrast, the uptake of T1-201, a potassium analog, does directly involve the sodium-potassium ATPasepump.

C. Incorrect. Tc-99m sestamibi distributes into tissues with relatively high mitochondrial content. Thepresence of a negative plasma membrane potential and high mitochondrial content are thought to explainthe normal uptake in such organs as the heart, liver, kidney, and skeletal muscle.

D. Incorrect. Tc-99m sestamibi retention is related to membrane potential.

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.

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