Key points
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ECFs on nuclear SPECT MPI are not uncommon and can be easily missed.
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ECFs are seen in 1.7% (0-2.8%) of all cases, and 50% of these are unsuspected prior to the study.
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There is a large variability in the incidence of ECFs, depending on the reader’s expertise.
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27% of breast uptake lesions and 46% of focal lung uptake lesions are malignant.
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Patients with ECFs, such as a hiatal hernia, pericardial effusion, pulmonary embolism, aortic dissection, splenomegaly, gallbladder disease, and bone lesions, may have symptoms that can often mimic cardiac symptoms.
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Identifying and reporting ECFs can alert the treating physician to pursue a different diagnostic pathway.
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ECFs are best identified while viewing the raw (unprocessed planar) data in a cine format (cinematic projection).
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ECFs can be small or large and they can be single or multiple
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ECFs can be detected because of either increased (increased vascularity) or decreased (attenuation) tracer concentration in a region of interest.
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Tracer uptake is increased with inflammation, hypermetabolic activity, and malignancy (primary or metastatic).
Background
“Perfusion” tracers such as Tl-201, Tc-99m sestamibi, and Tc-99m tetrofosmin are distributed to various organs according to regional MBF. Since resting MBF represents only ~ 4% of cardiac output, it is clear that most of the injected tracer dose is deposited outside the myocardium. These regions include the muscles, liver, kidneys, brain (in the case of Tl-201 only), bowel, salivary glands, and thyroid gland, to name just a few. There is also some activity in the lungs in the form of diffuse activity, which, in the case of Tl-201, has been used as a useful marker of elevated LV filling pressure. This type of activity should not be confused with the localized extracardiac activity being discussed in this chapter. At times, tracer activity is either detected at sites where it should not be or is not detected at sites where it should be. These constitute collectively incidental findings, which may in a given patient be more important than the cardiac perfusion study itself. If not detected and reported, a poor outcome might follow (e.g., from undiagnosed breast or lung cancer). Most of these incidental findings are detected by careful review of the rotating images; few, if any, are detected on tomographic slices or polar maps!
The most common ECFs are summarized in Table 16-1 . We will present a series of case examples to illustrate the pertinent findings.
| Defect | Location | Causes |
|---|---|---|
| Decreased uptake | Thorax | Permanent pacemaker/defibrillator |
| Pleural effusion | ||
| Pericardial effusion | ||
| Widened mediastinum/aortic aneurysm/dissection | ||
| Breast implants | ||
| Abdomen | Liver (cyst, cirrhosis, ascites) | |
| Gallbladder stones/Cholecystitis | ||
| Kidney (cyst, congenital absence) | ||
| Increased uptake | Head & neck | Thyroid (poor labeling, adenoma, malignancy, goiter) |
| Parathyroid (adenoma, hyperplasia, malignancy) | ||
| Thorax | Thymoma | |
| Hiatal hernia | ||
| Elevated hemi-diaphragm | ||
| Sarcoidosis (hilar/mediastinal/lung fibrosis) | ||
| High lung to heart (L/H) Tl-201 uptake | ||
| Lung nodules (primary or metastatic) | ||
| Breast (carcinoma, nodules, lactating) | ||
| Axillary (contamination, lymphangitic spread) | ||
| Bone (multiple myeloma, severe anemia) | ||
| Abdomen | Liver (hepatocellular cancer, metastasis) | |
| Stomach (poor labeling) | ||
| Splenomegaly | ||
| Cloth/skin | Contamination/residual activity at site of injection | |
| Miscellaneous | Dilated RV/pulmonary thromboembolism |
Case 16-1
ICD/Pacemaker ( Figure 16-1 )
A 64-year-old man with ischemic cardiomyopathy (LVEF of 25%), status post placement of an ICD, underwent Tc-99m sestamibi stress/rest SPECT MPI to evaluate his recurrent chest pain. The rest raw image demonstrated a dilated heart with a photopenic area in the left upper chest at the site of the ICD.
Comments
Permanent pacemakers and/or ICDs are commonly placed in the left or right subclavicular regions of the chest. On the raw images, they produce a significant photopenic area that can readily be identified unless a small field of view gamma camera is used and the position of the heart is at the bottom of the field of view, rather than at the center.
Case 16-2
Pleural Effusion ( Figure 16-2 )
A 58-year-old man underwent stress MPI prior to liver transplantation because of dyspnea on exertion. Significant physical exam findings included decreased breath sounds in the left lung field, hepatomegaly, positive fluid wave, and pedal edema. His laboratory values were significant for pancytopenia, acute kidney injury, mildly elevated bilirubin, and hypoalbuminemia. Stress SPECT MPI showed normal perfusion and an LVEF of 75%. The raw cine image ( Figure 16-2, A ) showed a large photopenic area shadowing almost the entire left lung field, consistent with a pleural effusion. The chest radiograph confirmed the diagnosis and showed a large pleural effusion ( Figure 16-2, B ). On the raw cine images, there was also a photopenic area around the liver, consistent with ascites ( Figure 16-2, C ). The field of view did not visualize the spleen, but the abdominal ultrasound did show significant ascites and splenomegaly.
Comments
Pleural effusions are common in patients with liver cirrhosis and hypoalbuminemia, but are also common in patients with congestive heart failure, lung cancer, and other conditions. Large effusions compress the lung and attenuate any lung activity, giving rise to a reverse pattern of lung activity (decreased rather than increased).
Case 16-3
Pericardial Effusion ( Figure 16-3 )
A 61-year-old woman with hypertrophic cardiomyopathy, no known coronary artery disease, class III-IV New York Heart Association heart failure symptoms, and symptomatic atrial fibrillation was initially referred for ablation therapy using pulmonary vein isolation. She was volume-overloaded on physical examination. After diuresis, she underwent stress SPECT MPI with Tc-99m sestamibi that showed normal perfusion and an LVEF of 57%. The raw cine image ( Figure 16-3. A ) showed a large photopenic area surrounding the heart, consistent with a pericardial effusion. Gated SPECT images ( Figure 16-3. B ) demonstrate swinging heart motion. 2D transthoracic echocardiogram confirmed the presence of a large (25 mm) pericardial effusion, but there were no echocardiographic signs of cardiac tamponade.
Comments
The diagnosis of pericardial effusion by SPECT MPI is uncommon, but there are multiple published case reports. The raw cine images picked up a large photopenic area around the heart, suggestive of pericardial effusion that was not suspected by history or physical examination. The ECG showed atrial fibrillation but no electrical alternans, while the gated SPECT images demonstrated the swinging/translational motion of the heart ( Figure 16-3, B , and Video 16-1).
Case 16-4
Aortic Dissection ( Figure 16-4 )
A 71-year-old woman presented to the ED with sudden onset of sharp chest pain, radiating to the neck and left shoulder. The pain was associated with nausea, diaphoresis, dyspnea, and dysphagia and was minimally relieved with sublingual nitroglycerin. Her past medical history was significant for hypertension, hyperlipidemia, and atrial fibrillation. Her medication list included warfarin, digoxin, lisinopril, HCTZ, and atenolol. She denied tobacco, alcohol, or illicit drug use. Her mother died of heart disease at age 40.
On physical exam, she appeared ill and in pain. Blood pressure was 152/68, pulse 81 irregular, and respirations were 24/min. She was afebrile, saturating 98% on a 2 L nasal cannula. Significant findings on exam included an increased jugular venous distention (10 cm) and a grade 2:6 systolic ejection murmur at the left lower sternal border.
Laboratory work-up was unremarkable except for a therapeutic international normalized ratio and intermediate troponin levels. The ECG ( Figure 16-4, A ) showed atrial fibrillation with non-specific T-wave changes. The chest radiograph ( Figure 16-4, B ) showed mediastinal enlargement, but was interpreted as having no significant change compared to one performed a year ago. She underwent a rest Tc-99m sestamibi SPECT MPI and was injected during active chest pains while in the ED. Rest SPECT MPI ( Figure 16-4, C ) revealed normal perfusion, the LVEF was 50% on gated images. She was admitted to the cardiac floor for monitoring. Shortly after, she had a cardiac arrest with pulseless electrical activity. She expired despite aggressive resuscitative efforts. Autopsy revealed a type A aortic dissection complicated by retrograde dissection with hemopericardium and hemothorax ( Figures 16-4, D, E ).The raw images showed a widened mediastinum and a photopenic area surrounding the heart, consistent with a pericardial effusion ( Figure 16-4F ).
Comments
Ascending aortic dissection can mimic acute coronary syndrome and should always be on the differential diagnosis, especially with such a clinical presentation. When suspected, CT chest or transesophageal echocardiogram should be promptly performed followed by emergency surgery, if positive.
Case 16-5
Breast Implants ( Figure 16-5 )
A 55-year-old woman with alcoholic liver cirrhosis underwent stress SPECT MPI with Tc-99m sestamibi as part of the liver transplant work-up. Raw cine image demonstrated well-defined symmetrical breast shadows that are consistent with breast implants ( Figure 16-5, A ).
Comments
Although breast implants are performed for cosmetic reasons, many are done after mastectomy for breast cancer. It is important to be diligent while looking at the raw images so as not to miss a recurrent breast cancer. Often a rim of breast tissue is seen overlying the implant anteriorly and can best be appreciated on cine images. The breast shadows appear symmetric and central in location. The attenuation by either natural breast or breast implant varies considerably and is not directly related to size. Breast tissue proper is more attenuating than fat tissue, which is abundant in redundant breasts ( Figures 16-5, B and C ).
Case 16-6
Liver Cyst ( Figure 16-6 )
A 91-year-old woman presented to the ED with nausea, vomiting, right-sided atypical chest pain, and upper abdominal pain. Stress/rest Tc-99m sestamibi SPECT MPI was normal. The raw cine image, however, showed photopenic areas in the liver suggestive of liver cysts ( Figure 16-6, A ). She underwent CT of the abdomen that showed multiple low attenuation lesions within the liver, predominantly medial segment left lobe, consistent with cysts, the largest 6.1 cm in size ( Figure 16-6, B ).
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