Answers to Unknown Case Sets

What is the most likely diagnosis? Unobstructed patulous collecting system of the right kidney with prompt washout of activity from the collecting system after Lasix.

If 370 MBq (10 mCi) of ^99m TcO ₄ ⁻ had been administered to the patient inadvertently instead of ^99m Tc-MAG3, would this constitute a reportable “medical event”? No. An administration of a wrong radiopharmaceutical is reportable only if it causes an effective whole-body dose exceeding 0.05 Sv (5 rem) or 0.5 Sv (50 rem) to any organ. This does not occur with most diagnostic doses.

What is the difference in mechanism of renal excretion between DTPA and MAG3? DTPA is predominantly filtered whereas MAG3 is excreted by proximal tubules with minimal filtration (about 2%).

What is the likely diagnosis?

• A.

  Cortical atrophy with ventricular CSF reflux

• B.

  Communicating arachnoid cyst

• C.

  CSF leak

• D.

  Ventricular shunt obstruction

• E.

  Normal pressure hydrocephalus

• Answer E. Normal pressure hydrocephalus (NPH).

What characteristics differentiate this from a normal study? Prominent early ventricular entry with persistence and lack of “ascent” of activity over the cerebral convexities at 24 hours.

Identify the anatomy on these images. In this case, the heart-shaped central activity is abnormal entry into the bodies and anterior horns of the lateral ventricles. The bilateral adjacent foci are the inferior (temporal) horns of the ventricles. Activity immediately below this is in the basal cisterns. In normal patients, activity is seen on the anterior view as a trident with activity in the interhemispheric (central) and sylvian (bilateral) cisterns with no persistent ventricular activity.

Regarding the images, which of the following is/are true?

• A.

  The results may be due to improper energy window setting.

• B.

  Energy peaking is typically done using the activity in the patient.

• C.

  The energy window should be 20% and centered at 160 keV.

• D.

  A collimator defect was likely present on the posterior camera head.

• E.

  The posterior camera head may be too far from the patient.

• Answers are A and E. The bone scan demonstrates loss of resolution on the posterior image. This may be caused by the posterior camera head being off-peak (not set for the correct energy window [140 keV] for ^99m Tc), the posterior camera head being too far from the patient, or a camera electronic malfunction. Peaking is not typically done using activity in the patient due to excessive scatter.

What is the finding? Gastrointestinal hemorrhage at the hepatic flexure of the colon. (Activity throughout the blood pool, including the heart, aorta, and iliac vessels, identifies this as a ^99m Tc RBC scan.)

What bleeding rate is necessary to reliably detect the bleeding with angiography and scintigraphy? 1.0 mL/min with angiography and about 0.2 mL/min on scintigraphy.

If the study had been negative, what would be the next step in management? Imaging can be continued or, if the patient appears to be bleeding again within 24 hours after ^99m Tc RBC administration, he or she can be returned for reimaging without reinjection, to assess for intermittent bleeding.

What is the most likely diagnosis? Most cold thyroid nodules are due to colloid cysts, but about 10% to 20% may be thyroid cancer.

What is the differential diagnosis? A solitary cold nodule is a nonspecific finding. The common differential includes thyroid adenoma, colloid cyst, or thyroid cancer.

What is the next step in management? If not a simple cyst on ultrasound, fine-needle aspiration.

What is the most likely diagnosis?

• A.

  Dextrocardia

• B.

  Breast attenuation artifact

• C.

  Diaphragmatic attenuation artifact

• D.

  Large anterior-apical infarct

• E.

  Ischemic dilatation

• Answer D. Large anterior-apical infarct

Are there important ancillary findings? There is a severe fixed anterior-apical defect with the ventricular walls diverging toward the apex (the “trumpet sign”), consistent with aneurysm formation in a region of infarction.

What is the route of exctetion of ^99m Tc-sestamibi? Biliary to bowel. Nearby liver, biliary, and bowel activity must be taken into account in timing the images to minimize artifacts. The organ receiving the highest dose is the gallbladder, or the colon if the gallbladder is absent.

What is the most likely primary pathology? Lung cancer.

Is this patient amenable to surgery? No, because there are contralateral mediastinal metastases.

Is bronchioalveolar cancer (adenocarcinoma in situ) typically FDG-avid? No.

What type of scan is this? A bone scan.

What is the most likely diagnosis?

• A.

  Hepatic necrosis

• B.

  Hepatitis

• C.

  Budd-Chiari syndrome

• D.

  Liver metastases

• Answer D. Multifocal or patchy diffuse uptake in an enlarged liver consistent with hepatic metastases. Hepatic necrosis could also be considered but is much less common. Mucinous tumors of the colon, ovary, and breast may calcify and have uptake.

What are some other causes of soft tissue uptake on bone scans? Infarcts, malignant ascites and malignant pleural effusions, lymphoma, lung cancer, meningioma, osteogenic sarcoma, dystrophic calcification, uterine fibroids, amyloidosis, dermatomyositis, calcific tendonitis, renal failure, hyperparathyroidism, mastitis, hematomas, and diffuse or focal soft tissue inflammation.

Assuming the ventilation scan is normal and the chest radiograph shows hyperinflation, what is the probability of pulmonary embolism? Low probability for pulmonary embolism.

Does this appearance have a specific name? This is a “fissure sign” (right major and minor fissures) seen with pleural fluid or pleural thickening (often appearing in patients with COPD).

What is the “stripe” sign and what is its significance, if any? The stripe sign is different from the fissure sign. The stripe sign refers to a stripe of activity, between a perfusion defect and the pleura, indicating preserved perfusion in the subpleural lung. It is characteristic of COPD and without other significant findings indicates a very low probability of pulmonary embolism.

Regarding the image, which of the following is/are true?

• A.

  The meter reading indicates that the package is likely damaged, and the delivery carrier and the NRC should be notified.

• B.

  The radioactive II label means that this is a Type B package.

• C.

  The limit for radiation dose at 1 meter from this package is 1 mrem (10 µSv) per hour.

• D.

  A wipe test of the surface of this package is required upon receipt.

• E.

  Such packages are required to be monitored within 3 hours of receipt or within the first 3 hours of the next business day.

• Answers C, D, and E are true.

What is the most likely diagnosis?

• A.

  Colon cancer metastasis

• B.

  Tuberculosis

• C.

  Lymphoma

• D.

  Hemorrhagic stroke

• Answer C. ¹⁸ F-FDG-avid brain lymphoma seen as a homogeneously hypermetabolic mass.

How would an area of central necrosis have changed your diagnosis? An area of necrosis would be common in a high-grade astrocytoma.

How useful is this test in a patient with suspected CNS metastases from lung cancer? This would be a poor choice because most metastases are less metabolic than normal brain tissue and may not be apparent on FDG PET imaging. An enhanced MRI is the best test.

What are the findings? Decreased activity in the frontal and frontotemporal regions on a ^99m Tc-HMPAO SPECT brain scan.

What are the differential possibilities? These findings are characteristic of frontotemporal dementia (Pick disease) but can also be seen in schizophrenia, depression, and supranuclear palsy. Atypical Alzheimer disease may uncommonly present in this manner.

Does the distribution of activity represent regional metabolism or regional blood flow? HMPAO is a marker of regional blood flow, not metabolism.

What is the most likely diagnosis?

• A.

  Regenerating nodule

• B.

  Focal nodular hyperplasia

• C.

  Hepatoma

• D.

  Hemangioma

• E.

  Recent hematoma

• Answer C. Hepatoma. Gallium-67 is very sensitive for the detection of hepatocellular carcinoma. However, the test of choice if a hepatoma is suspected is a three-phase CT scan.

What other liver lesions may accumulate gallium? Abscess, lymphoma, and metastasis, with sensitivity varying with the primary tumor type .

What are appearances of hepatic adenoma and focal nodular hyperplasia on a ^99m Tc-sulfur colloid liver scan? Adenomas will typically appear cold, whereas FNH typically has Kupffer cells and thus may appear to have the same activity as the liver or even increased.

What type of scan is this? Hepatobiliary .

What is the diagnosis?

• A.

  Bile leak

• B.

  Free pertechnetate from poor radiopharmaceutical labeling

• C.

  Biliary atresia

• D.

  Choledochal cyst

• E.

  Hepatitis

• The correct answer is E, neonatal hepatitis, as evidenced by the small bowel activity and inclusion of the entire body on the image indicating a neonate or small child. Premedication for 5 to 7 days with oral phenobarbital (2.5 mg/kg bid) may be used to improve hepatic excretion and test accuracy.

In an effort to keep radiation doses low to children, what administered activity should be given to this 2-kg infant? 1.0 mCi (37 MBq). Nobody expects you to memorize weight-specific doses in children, but you should know where to look them up. See Appendix D .

What is the most likely diagnosis?

• A.

  Shin splints

• B.

  Hyperparathyroidism

• C.

  Hypertrophic osteoarthropathy (HOA)

• D.

  Renal failure

• E.

  Bone contusion

• Answer C. Hypertrophic pulmonary.

Is there an incidental finding? Yes, right nephrectomy .

What other radiopharmaceutical can be used for bone scans besides ^99m Tc-MDP? PET/CT bone scans can be done with ¹⁸ F-sodium fluoride. This radiopharmaceutical is very sensitive but has a several-fold higher cost and a sevenfold higher radiation dose than does MDP.

What is the most likely diagnosis?

• A.

  Fat emboli

• B.

  Pneumonia

• C.

  COPD

• D.

  Metastases

• E.

  Multiple thromboemboli

• Answer C. Chronic obstructive pulmonary disease (COPD). There are multiple matched ventilation/perfusion abnormalities bilaterally with delayed clearance of ¹³³ Xe from the lungs.

What category is this according to PIOPED II criteria? Very low.

A large amount of central airway deposition on a ^99m Tc-DTPA aerosol scan is an indication of what entity? COPD.

What is the most likely diagnosis? Superscan with diffuse skeletal metastases.

Under what circumstances would you treat such a patient with ⁸⁹ Sr-chloride or similar therapeutic radiopharmaceutical? Intractable bone pain with active blastic metastases should be present, and the WBC and platelet counts should be above 2400/µL and 60,000/µL, respectively. Optimally, renal function should be normal or the administered dose should be reduced to accommodate renal dysfunction, depending on its severity.

What radiation protection precautions are necessary after ⁸⁹ Sr treatment? Because of beta (and no gamma) emission, few restrictions are necessary. Excretion is urinary and, to a lesser extent, fecal, which requires some instructions regarding frequency of urination to reduce bladder dose, sitting to urinate, and flushing the toilet twice afterward. Life expectancy should be at least 3 months because many states have restrictions on cremation, etc.

What is the most likely diagnosis? Lymphoma based upon extensive adenopathy and multiple lung lesions. Other possibilities include metastatic melanoma and diffuse infection in an immunocompromised patient.

What is/are the main use(s) for FDG PET/CT in lymphoma? It is useful for staging, assessing treatment response and possible change of therapy, and detection of suspected recurrence.

Are MALT lymphomas typically FDG-avid? No .

What is the most likely diagnosis? Multinodular goiter.

Is fine-needle aspiration biopsy warranted? In general, no, because the cold areas commonly are a result of nonfunctioning or poorly functioning adenomas and are much less likely to be cancer than is a solitary cold nodule. A dominant nodule, sonographically suspicious nodule, or MNG in a child deserves further characterization.

With what radiopharmaceutical was this scan performed? Significant activity in the salivary glands indicates that it was performed with ^99m Tc-pertechnetate rather than ¹²³ I.

In treating toxic MNG with ¹³¹ I, is the administered activity generally more or less than when treating Graves disease? More, largely because the lower, heterogeneously distributed uptake of radioiodine requires a larger dose.

Is there a problem with delivery of this package containing radioactive material? Yes, it is not in a secured location, and the office almost certainly has no precautionary sign indicating “radioactive materials.”

What are the requirements concerning transport of a radioactive package? Material must be in an approved, usually Type A, container with a label indicating the transport index (TI) as well as the radiopharmaceutical and contained activity.

What are the requirements concerning acceptance? Packages must be secured, examined, monitored, and logged in. This procedure should be performed within 3 hours of receipt if it is received during normal working hours, otherwise within 3 hours on the next work day.

What is the diagnosis? Bile leak with activity in the porta hepatis and right paracolic gutter.

Is the gallbladder present? No. In this case, the patient has had a recent cholecystectomy. Leaking bile commonly pools in the porta hepatis, gallbladder fossa, or around the liver (the “reappearing liver” sign). Obtaining a history of prior surgery is critical for accurate interpretation of the images.

What special views can be helpful? Right lateral decubitus and pelvic views can often be useful to search for bile flowing to other locations in the abdomen or pelvis.

What is the most likely diagnosis? Brain death, as evidenced by no intracranial perfusion on the ^99m Tc-pertechnetate study. The actual diagnosis of brain death should not be made by nuclear imaging tests alone but requires consideration of clinical parameters.

Can this study be done with ^99m Tc-hexamethylpropyleneamine oxime (HMPAO)? Yes, although it is more costly than ^99m Tc-pertechnetate or DTPA.

What would be the significance of sagittal sinus activity in a patient without obvious arterial phase activity? The significance is somewhat controversial, but most of the patients have a grave prognosis, and slight venous activity does not contradict the diagnosis of brain death.