Multimodality imaging of mediastinal masses and mimics.

A wide variety of neoplastic and nonneoplastic conditions occur in the mediastinum. Imaging plays a central role in the evaluation of mediastinal pathologies and their mimics. Localization of a mediastinal lesion to a compartment and characterization of morphology, density/signal intensity, enhancement, and mass effect on neighboring structures can help narrow the differentials. The International Thymic Malignancy Interest Group (ITMIG) established a cross-sectional imaging-derived and anatomy-based classification system for mediastinal compartments, comprising the prevascular (anterior), visceral (middle), and paravertebral (posterior) compartments. Cross-sectional imaging is integral in the evaluation of mediastinal lesions. Computed tomography (CT) and magnetic resonance imaging (MRI) are useful to characterize mediastinal lesions detected on radiography. Advantages of CT include its widespread availability, fast acquisition time, relatively low cost, and ability to detect calcium. Advantages of MRI include the lack of radiation exposure, superior soft tissue contrast resolution to detect invasion of the mass across tissue planes, including the chest wall and diaphragm, involvement of neurovascular structures, and the potential for dynamic sequences during free-breathing or cinematic cardiac gating to assess motion of the mass relative to adjacent structures. MRI is superior to CT in the differentiation of cystic from solid lesions and in the detection of fat to differentiate thymic hyperplasia from thymic malignancy.

Pearls and pitfalls in imaging of mediastinal masses.

In imaging of the mediastinum, advances in computed tomography (CT), and magnetic resonance imaging (MRI) technology enable improved characterization of mediastinal masses. Knowledge of the boundaries of the mediastinal compartments is key to accurate localization. Awareness of distinguishing imaging characteristics allows radiologists to suggest a specific diagnosis or narrow the differential. In certain situations, MRI adds value to further characterize mediastinal lesions.

Implications for high-precision dose radiation therapy planning or limited surgical resection after percutaneous computed tomography-guided lung nodule biopsy using a tract sealant.

PURPOSE: Precision radiation therapy such as stereotactic body radiation therapy and limited resection are being used more frequently to treat intrathoracic malignancies. Effective local control requires precise radiation target delineation or complete resection. Lung biopsy tracts (LBT) on computed tomography (CT) scans after the use of tract sealants can mimic malignant tract seeding (MTS) and it is unclear whether these LBTs should be included in the calculated tumor volume or resected. This study evaluates the incidence, appearance, evolution, and malignant seeding of LBTs. METHODS AND MATERIALS: A total of 406 lung biopsies were performed in oncology patients using a tract sealant over 19 months. Of these patients, 326 had follow-up CT scans and were included in the study group. Four thoracic radiologists retrospectively analyzed the imaging, and a pathologist examined 10 resected LBTs. RESULTS: A total of 234 of 326 biopsies (72%, including primary lung cancer [n = 98]; metastases [n = 81]; benign [n = 50]; and nondiagnostic [n = 5]) showed an LBT on CT. LBTs were identified on imaging 0 to 3 months after biopsy. LBTs were typically straight or serpiginous with a thickness of 2 to 5 mm. Most LBTs were unchanged (92%) or decreased (6.3%) over time. An increase in LBT thickness/nodularity that was suspicious for MTS occurred in 4 of 234 biopsies (1.7%). MTS only occurred after biopsy of metastases from extrathoracic malignancies, and none occurred in patients with lung cancer. CONCLUSIONS: LBTs are common on CT after lung biopsy using a tract sealant. MTS is uncommon and only occurred in patients with extrathoracic malignancies. No MTS was found in patients with primary lung cancer. Accordingly, potential alteration in planned therapy should be considered only in patients with LBTs and extrathoracic malignancies being considered for stereotactic body radiation therapy or wedge resection.

PET/CT Interpretative Pitfalls in Thoracic Malignancies.

Applications of positron emission tomography/computed tomography (PET/CT) in the thorax include the evaluation of solitary pulmonary nodules, staging and restaging of oncologic patients, assessment of therapeutic response, and detection of residual or recurrent disease. Accurate interpretation of PET/CT requires knowledge of the physiological distribution of [18F]-fluoro-2-deoxy-D-glucose, as well as artifacts and quantitative errors due to the use of CT for attenuation correction of the PET scan. Potential pitfalls include malignancies that are PET negative and benign conditions that are PET positive. Awareness of these artifacts and potential pitfalls is important in preventing misinterpretation that can alter patient management.

Staging Lung Cancer: Metastasis.

The updated eighth edition of the tumor, node, metastasis (TNM) classification for lung cancer includes revisions to T and M descriptors. In terms of the M descriptor, the classification of intrathoracic metastatic disease as M1a is unchanged from TNM-7. Extrathoracic metastatic disease, which was classified as M1b in TNM-7, is now subdivided into M1b (single metastasis, single organ) and M1c (multiple metastases in one or multiple organs) descriptors. In this article, the rationale for changes in the M descriptors, the utility of preoperative staging with PET/computed tomography, and the treatment options available for patients with oligometastatic disease are discussed.

Imaging of Metastases in the Chest: Mechanisms of Spread and Potential Pitfalls.

Pulmonary and pleural metastases are routinely identified on thoracic computed tomography. Pulmonary metastases are the most common pulmonary neoplasms and commonly originate from primary malignancies of the lung, breast, colon, pancreas, stomach, skin (ie, melanoma), head and neck, and kidney. Metastatic disease to the lungs may occur via 3 routes of spread: hematogenous, lymphatic, and endobronchial. Pleural metastases most commonly originate from primary malignancies of the lung and breast. Mechanisms of pleural metastatic involvement include hematogenous spread, direct invasion from a neighboring tumor, and retrograde lymphatic spread from the mediastinum. Awareness of the spectrum of appearances of metatastic disease in the chest is important in avoiding misinterpretation.

Imaging of Eosinophilic Lung Diseases.

Eosinophilic lung diseases encompass a broad range of conditions wherein patients present with pulmonary opacities and eosinophilia of the serum, pulmonary tissue, or bronchoalveolar lavage fluid. Many of these entities can be idiopathic or are secondary to parasitic infection, exposure to drugs, toxins, or radiation. These diseases exhibit a wide range of imaging findings, including consolidation, ground-glass opacities, nodules, and masses. Diagnoses often require bronchoalveolar lavage and/or biopsy to confirm respiratory eosinophilia and to exclude other entities, such as infection or malignancy. Treatment entails administration of corticosteroids, removal of inciting agents, and treatment of underlying infection.

Characterizing proton-activated materials to develop PET-mediated proton range verification markers.

Conventional proton beam range verification using positron emission tomography (PET) relies on tissue activation alone and therefore requires particle therapy PET whose installation can represent a large financial burden for many centers. Previously, we showed the feasibility of developing patient implantable markers using high proton cross-section materials ((18)O, Cu, and (68)Zn) for in vivo proton range verification using conventional PET scanners. In this technical note, we characterize those materials to test their usability in more clinically relevant conditions. Two phantoms made of low-density balsa wood (~0.1 g cm(-3)) and beef (~1.0 g cm(-3)) were embedded with Cu or (68)Zn foils of several volumes (10-50 mm(3)). The metal foils were positioned at several depths in the dose fall-off region, which had been determined from our previous study. The phantoms were then irradiated with different proton doses (1-5 Gy). After irradiation, the phantoms with the embedded foils were moved to a diagnostic PET scanner and imaged. The acquired data were reconstructed with 20-40 min of scan time using various delay times (30-150 min) to determine the maximum contrast-to-noise ratio. The resultant PET/computed tomography (CT) fusion images of the activated foils were then examined and the foils' PET signal strength/visibility was scored on a 5 point scale by 13 radiologists experienced in nuclear medicine. For both phantoms, the visibility of activated foils increased in proportion to the foil volume, dose, and PET scan time. A linear model was constructed with visibility scores as the response variable and all other factors (marker material, phantom material, dose, and PET scan time) as covariates. Using the linear model, volumes of foils that provided adequate visibility (score 3) were determined for each dose and PET scan time. The foil volumes that were determined will be used as a guideline in developing practical implantable markers.

Role of imaging in the diagnosis, staging, and treatment of thymoma.

Thymoma is a rare mediastinal neoplasm but is the most common primary neoplasm of the anterior mediastinum. There have been only a few published reports assessing this disease. Furthermore, many of these reports are from a single institution and span several decades, which may lead to potentially misleading conclusions related to diagnosis, staging, and treatment. Computed tomography is the imaging modality of choice for evaluating thymoma and can help distinguish thymoma from other anterior mediastinal abnormalities. Tumor stage and extent of resection are the most important prognostic factors. Tumors that are encapsulated and are amenable to complete resection have a good prognosis, whereas invasive and unresectable tumors have a poor prognosis regardless of their histologic characteristics. Radiologists must be aware of the full spectrum of imaging findings of thymoma, the standard guidelines for diagnostic evaluation, and how imaging findings affect therapeutic decisions.

Multidetector CT of solitary pulmonary nodules.

With the increasing use of MDCT, more solitary pulmonary nodules are being detected. Although the majority of these lesions are benign, lung cancer constitutes an important consideration in the differential diagnosis of solitary pulmonary nodules. The goal of management is to correctly differentiate malignant from benign nodules to ensure appropriate treatment. Stratifying patients' risk factors for malignancy, including patient age, smoking history, and history of malignancy, is essential in the management of solitary pulmonary nodules. In terms of radiologic evaluation, obtaining prior films is important to assess for nodule growth. The detection of certain patterns of calcification and stability for 2 years or more have historically been the only useful findings for determining whether a nodule is or is not benign. However, recent technological advances in imaging, including MDCT and PET/CT, have improved nodule characterization and surveillance. For solid nodules, CT enhancement of less than 15 HU and hypometabolism on PET (SUVmax <2.5) favor a benign etiology. Potential pitfalls in nodule enhancement and PET evaluation of solitary pulmonary nodules include infectious and inflammatory conditions. Stratified according to patient risk factors for malignancy and nodule size, recent guidelines for the management of incidentally detected small pulmonary nodules have been useful in decision analysis. An important exception to these guidelines is the evaluation and management of the subsolid nodule. These lesions are not suitable for CT enhancement studies and may show low metabolic activity on PET imaging. Due to their association with bronchioloalveolar carcinoma and adenocarcinoma, subsolid nodules require a more aggressive approach in terms of reassessing serial imaging and/or obtaining tissue diagnosis. As data from the low-dose CT lung cancer screening trials are analyzed and further studies with new imaging techniques are performed, management strategies for the imaging evaluation of the solitary pulmonary nodule will continue to evolve.

Multidetector CT of solitary pulmonary nodules.

With the increasing use of multidetector CT, small nodules are being detected more often. Although most incidentally discovered nodules are benign, usually the sequelae of pulmonary infection and malignancy, either primary or secondary, remains an important consideration in the differential diagnosis of solitary pulmonary nodules. This article reviews the role of imaging in the detection and characterization of solitary pulmonary nodules. Strategies for evaluating and managing solitary pulmonary nodules are also discussed.

Tumor cavitation during therapy with antiangiogenesis agents in patients with lung cancer.

PURPOSE: Treatment of lung cancer patients with antiangiogenesis agents is a new promising paradigm. Tumor cavitation is frequently noted in these patients, but the clinical significance of this finding has not been fully determined. Our purposes were to evaluate the frequency, imaging characteristics, and clinical outcome of patients receiving antiangiogenesis agents who develop tumor cavitation, and correlate these findings with therapy related adverse events, especially hemoptysis. METHODS: Retrospective analysis of lung cancer patients treated with antiangiogenesis agents in MD Anderson Cancer Center between June 1998 and June 2005. Clinical data were retrieved from medical records, and chest imaging findings were documented. RESULTS: One hundred and twenty-four patients were treated in 10 different trials. All patients had advanced lung cancer and failed previous chemotherapy. Seventeen patients developed tumor cavitation during the trial (14%; median time to event, 1.8 months; range, 0.7-6.2 months), 16 patients (13%) had preexisting cavitary tumors, and 91 (73%) did not develop cavitation. Cavity formation was more common with squamous cell histology (p = 0.04) but was not associated with hemoptysis (p = 0.12), tumor location (central versus peripheral), imaging characteristics, progression-free survival (p = 0.56), or overall survival (p = 0.33). Hemoptysis was noted in five patients (median time to event, 1.3 months; range, 0.8-2.9 months). One of five patients with hemoptysis was fatal in a cavitary squamous cell tumor. Additional adverse events were hypertension, rash, and proteinuria, none associated with cavitation. CONCLUSION: Development of tumor cavitation is not rare in lung cancer patients treated with antiangiogenesis agents, but the clinical implications are minimal in most cases.

CT, positron emission tomography, and MRI in staging lung cancer.

Lung cancer is a common malignancy and remains the leading cause of cancer-related deaths in both men and women in the United States. Imaging plays an important role in the detection, diagnosis, and staging of the disease as well as in assessing response to therapy and monitoring for tumor recurrence after treatment. This article reviews the staging of the two major histologic categories of lung cancer-non-small-cell lung carcinoma (NSCLC) and small-cell lung carcinoma-and emphasizes the appropriate use of CT, MRI, and positron emission tomography imaging in patient management. Also discussed are proposed revisions of the International Association for the Study of Lung Cancer's terms used to describe the extent of NSCLC in terms of the primary tumor, lymph nodes, and metastases descriptors.

PET/CT of esophageal cancer: its role in clinical management.

Positron emission tomography (PET)/computed tomography (CT) has important utility and limitations in the initial staging of esophageal cancer, evaluation of response to neoadjuvant therapy, and detection of recurrent malignancy. Esophageal cancer is often treated by using a combined modality approach (chemotherapy, radiation therapy, and esophagectomy); correct integration of PET/CT into the conventional work-up of esophageal cancer requires a multidisciplinary approach that combines the information from PET/CT with results of clinical assessment, diagnostic CT, endoscopic gastroduodenoscopy, and endoscopic ultrasonography. PET/CT has limited utility in T staging of esophageal cancer and relatively limited utility in detection of dissemination to locoregional lymph nodes. However, PET/CT allows detection of metastatic disease that may not be identifiable with other methods. PET/CT is not sufficiently reliable in the individual patient for determination of treatment response in the primary tumor. Interpretation of PET/CT results is optimized by understanding the diagnostic limitations and pitfalls that may be encountered, together with knowledge of the natural history of esophageal cancer and the staging and treatment options available.

Pedicle muscle flaps in intrathoracic cancer resection: imaging appearance and evolution.

Pedicle muscle flaps that are used to enhance surgical site integrity after thoracic cancer resections may simulate a recurrent mass at postoperative imaging. However, such flaps have a characteristic appearance and location that should allow their differentiation from a solid mass or fluid collection. The location and appearance of a flap depend on the type of muscle used (whether intercostal, serratus anterior, or latissimus dorsi) and the extent of resection. The appearance also varies according to the presence and amount of fat and calcification in the flap. Most flaps have fat strands along the flap axis that increase in size over time. Linear areas of calcification also may occur because of the inclusion of periosteum in a flap, or more extensive calcification may lead to ossification over time. Uncomplicated flaps do not show substantial radionuclide uptake at positron emission tomography (PET), but areas of extensive calcification may show increased uptake similar to that in bone. Vessels also may be seen within a flap, particularly if the flap has a high fat content; and enhancing vessels frequently are evident at contrast material-enhanced computed tomography (CT). The magnetic resonance (MR) imaging characteristics of flaps are similar to those of normal fat and muscle. Although CT is the modality most often used for follow-up imaging, PET or MR imaging may be helpful in cases in which the CT findings are questionable.

Incidental pulmonary emboli in oncology patients: prevalence, CT evaluation, and natural history.

PURPOSE: To retrospectively determine the prevalence and natural history of incidental pulmonary emboli in oncology patients, the number of such cases reported at initial thoracic computed tomographic (CT) image interpretation, and the factors that contribute to underdiagnosis. MATERIALS AND METHODS: Institutional review board approval, which included HIPAA-compliant access to protected health information and waived patient consent requirements, was obtained for this retrospective study. Four hundred three consecutive oncology patients (199 male, 204 female; age range, 14-87 years; mean age, 55 years) in whom adequate-quality multidetector thoracic CT was performed within a 10-day period for indications other than pulmonary emboli assessment were identified. There were 31 (7.7%) inpatients at the time of imaging. Each imaging case was reviewed by two independent radiologists, and all pulmonary emboli were confirmed by a panel of three thoracic radiologists. Clinical charts were reviewed for demographic data, embolus detection, and outcomes up to 2 years after the initial examination. Patient groups were compared by using chi2 and one-sided binomial tests. RESULTS: Sixteen (4.0%) of the 403 patients had pulmonary emboli. The highest prevalences were in patients with gynecologic malignancies (two of 13, 15%) and in those with melanoma (four of 41, 10%). Four (25%) of the 16 patients with emboli were identified at initial clinical CT image interpretation, and all had multiple emboli involving at least the lobar arteries. Missed emboli typically were solitary and involved smaller arteries; no other confounding factors were identified. Six (60%) of 10 patients with emboli who underwent any lower extremity imaging had deep vein thrombosis. With the exception of one patient, who was transferred back to the referring physician and lost to follow-up, all patients with reported pulmonary emboli were treated. Two patients had subsequent embolic events: one death despite treatment and one recurrent embolus in a nontreated patient. CONCLUSION: Incidental pulmonary emboli were seen in 16 (4%) oncology patients but were initially reported in only four of them. The small size of involved arteries contributes to the failed detection at initial CT image interpretation, and patients with emboli in these small vessels may have deep vein thrombosis or recurrent emboli.

Preoperative chemo-radiation-induced ulceration in patients with esophageal cancer: a confounding factor in tumor response assessment in integrated computed tomographic-positron emission tomographic imaging.

HYPOTHESIS: Positron emission tomography can be useful in predicting response of esophageal cancer after preoperative chemo-radiation therapy (CRT). We evaluated the use of integrated computed tomography (CT)-PET among patients with esophageal cancer being considered for resection after CRT. METHODS: Three reviewers blinded to clinical and pathologic staging retrospectively reviewed the CT-PET scans of patients with esophageal cancer after preoperative CRT who underwent esophagectomy. [F]-fluoro-2-deoxy-D-glucose uptake for residual malignancy was determined by visual analysis and semi-quantitatively when standardized uptake value (SUV) was > or =4. RESULTS: Forty-two patients underwent esophageal resection. Using visual analysis, CT-PET had a sensitivity of 47% and specificity of 58% in detecting residual malignancy. Using semi-quantitative analysis, 19 patients had a SUV > or =4 in the region of the primary esophageal tumor and were interpreted as having residual malignancy (sensitivity 43%, specificity 50%). Of these 19, six had complete pathologic response to CRT. These false-positive results, due to therapy-induced ulceration detected at endoscopy, limit the use of CT-PET alone in detecting residual malignancy. Similarly, sensitivity (25%) and specificity (73%) of endoscopy/biopsy in detecting residual malignancy were poor. However, the accuracy of CT-PET in detecting residual malignancy was improved when combined with endoscopic findings. In the absence of ulceration at endoscopy, 8 of 8 patients with SUV > or =4 after chemo-radiation had residual malignancy at surgery. CONCLUSIONS: CRT-induced ulceration results in false-positive results on CT-PET and precludes accurate detection of residual esophageal tumor. However, CT-PET in combination with endoscopy is useful in identifying patients with a high risk of residual tumor post-CRT.

Focal uptake of fluorodeoxyglucose by the thyroid in patients undergoing initial disease staging with combined PET/CT for non-small cell lung cancer.

PURPOSE: To retrospectively evaluate the prevalence of focal fluorodeoxyglucose (FDG) uptake by the thyroid gland on combined positron emission tomographic (PET) and computed tomographic (CT) scans in patients undergoing staging of newly diagnosed non-small cell lung cancer (NSCLC). MATERIALS AND METHODS: Institutional review board approval was obtained, informed consent was waived, and the study was Health Insurance Portability and Accountability Act-compliant. Whole-body PET/CT scans and medical records of 140 consecutive patients with newly diagnosed NSCLC (80 men, 60 women; mean age, 66 years; range, 39-89 years) were retrospectively reviewed by two experienced PET/CT scan readers. Maximum standardized uptake value (SUV) was calculated for FDG-avid thyroid foci. Corresponding thyroid CT findings were recorded in patients with focal increased FDG thyroid uptake. RESULTS: PET results showed that six patients (4.3%) had seven foci of increased FDG uptake in the thyroid. Five of the seven foci (in four patients) corresponded to a low-attenuation thyroid lesion on the non-enhanced CT scan. Lesions ranged in diameter from 0.8 to 2.5 cm. Four of the lesions were found to be papillary thyroid cancers at fine-needle aspiration biopsy. The fifth lesion was found to be benign at thyroidectomy. The remaining two patients did not have histologic confirmation of their thyroid lesion because no specific biopsy site was visualized on CT or sonographic images and lesions were considered benign. Maximum SUV of the thyroid cancers ranged from 3.0 to 32.9 (mean, 13.7). Maximum SUV of benign thyroid lesions ranged from 4.6 to 6.2 (mean, 5.4). CONCLUSION: Focal thyroid FDG uptake found during the initial staging of NSCLC at PET/CT indicates a high likelihood of primary thyroid cancer.

Integrated computed tomography-positron emission tomography in patients with potentially resectable malignant pleural mesothelioma: Staging implications.

BACKGROUND: Integrated computed tomography-positron emission tomography imaging with coregistration of anatomic and functional imaging data may improve the accuracy of malignant pleural mesothelioma staging. We evaluate the use of integrated computed tomography-positron emission tomography in patients with malignant pleural mesothelioma who are being considered for extrapleural pneumonectomy. METHODS: Twenty-nine patients with malignant pleural mesothelioma who were judged to be candidates for extrapleural pneumonectomy after clinical and conventional radiologic evaluation underwent whole-body integrated computed tomography-positron emission tomography and pathologic staging. Two reviewers blinded to the results of clinical and pathologic staging retrospectively evaluated computed tomography, positron emission tomography, and coregistered computed tomography-positron emission tomography images. Staging was performed according to the International Mesothelioma Interest Group TNM staging system. Histopathology and/or results of further radiologic evaluation or follow-up served as the reference standard. RESULTS: Integrated computed tomography-positron emission tomography provided additional information in 11 of 29 patients that precluded extrapleural pneumonectomy. The overall tumor stage was correctly classified in 21 of 29 patients. The tumor stage was correctly determined in 15 of 24 patients, 6 of whom had T4 (nonresectable) disease. The node stage was accurately determined in 6 of 17 patients. Extrathoracic metastases not identified by routine clinical and conventional radiologic evaluation were detected in 7 of 29 patients and were found to be diffuse (n = 2) or solitary (n = 5). CONCLUSIONS: Integrated computed tomography-positron emission tomography increases the accuracy of malignant pleural mesothelioma staging and is important in determining the appropriate therapy in patients being considered for extrapleural pneumonectomy.