Computed tomography and magnetic resonance imaging of mediastinal tumors

We describe the clinical, pathological, and imaging findings of mediastinal tumors with focus on thymic hyperplasia, thymic epithelial tumors, and germ cell tumors, malignant lymphoma, and various cystic masses. Chemical shift magnetic resonance imaging (MRI) is useful in characterization of the normal thymus and differentiation of hyperplastic thymus and thymic tumors. In contrast to noninvasive thymomas, invasive thymomas and thymic carcinomas show a more aggressive growth pattern. Local invasion and pleural spread are characteristic of invasive thymoma and mediastinal lymphadenopathy and distant metastasis suggest thymic carcinomas. Mature teratoma typically shows various computed tomography (CT) attenuation, and MR signal intensity depending on its contents and fat tissue and bone within the lesions are its characteristic findings. Seminomas typically have homogenous internal CT attenuation and MR signal intensity with minimal contrast enhancement. Nonseminomatous malignant germ cell tumors characteristically show prominent internal degenerative changes and invasion to the adjacent structures. In mediastinal lymphomas, a residual mass is common after treatment and MRI provides important information in distinguishing viable tumors from residual benign masses. Some mediastinal cysts may reveal high attenuation similar to solid lesions on CT depending on their contents and MRI can be useful in the differentiation of cystic masses from solid lesions.     

Normal and abnormal thymus in childhood: MR imaging

Magnetic resonance (MR) imaging studies of 47 children without thymic disease were compared with those of 14 children with proved thymic abnormalities (eg, lymphoma, leukemia, hyperplasia) to evaluate the spectrum of MR features of the normal and abnormal thymus and to determine the best indicators of thymic disease. In healthy children younger than 5 years of age, the thymus had a quadrilateral shape and biconvex lateral contours. Older children and adolescents had a triangular thymus with straight lateral margins. The thymus appeared homogeneous with a signal intensity slightly greater than that of muscle on T1-weighted images and close to that of fat on T2-weighted images. Qualitative evaluation of gross thymic morphology (size, shape, margins, and signal intensity) usually was sufficient for distinguishing between the normal and abnormal thymus. The abnormal thymus generally was enlarged, multilobular, or inhomogeneous because of the presence of cystic degeneration, hemorrhage, septations, fibrosis, or calcification on pathologic sections. In patients with lymphoma, the presence of associated lymphadenopathy also was helpful in distinguishing the normal from the abnormal thymus.     

MR imaging of the thyroid: comparison with scintigraphy in the normal and diseased gland

Spin-echo magnetic resonance (MR) imaging of the thyroid gland was performed in patients using a superconducting magnet operating at 0.35 T. There were 17 women and two men with an age range of 21-77 years. All of the patients with disease were also evaluated with scintigraphy and three of the four subjects with normal thyroid glands also had scintigraphy. Final diagnoses in the patients were normal gland in four, Graves disease in two, thyroid cyst in one, benign follicular adenoma in two, papillary cell carcinoma in one, Hürthle cell carcinoma in one, Hashimoto thyroiditis in one, and multinodular goiter in seven. The normal thyroid and surrounding anatomy were clearly demonstrated by intrinsic signal intensity differences of the tissues. The thyroid gland in Graves disease was enlarged and had homogeneously increased signal intensity at all pulse sequences compared with skeletal muscle and normal thyroid. The thyroid cyst and benign adenoma were well defined; however, the cyst displayed the greater signal intensity on more T2-weighted pulse sequences. The MR signal intensity features of multinodular goiter and Hashimoto thyroiditis appear similar to those of the normal gland. In cases of focal masses, MR could not reliably distinguish benign from malignant tumor. However, using intensity ratio data there was a statistically significant difference between solid and hemorrhagic cystic disease.     

Characterization of thymic lesions with F-18 FDG PET-CT: an emphasis on epithelial tumors

Thymic lesions may represent an unresolved diagnostic problem that often requires surgical procedure for an accurate diagnosis and staging. A noninvasive imaging study to determine the nature of thymic lesions would help to identify patients who are true candidates for surgery. Published preliminary clinical observations have suggested a role of fluorine-18 fluorodeoxyglucose (F-18 FDG) positron emission tomography-computed tomography (PET-CT) in the characterization of thymic lesions. Benign uptake of the thymus on F-18 FDG PET-CT is seen in children and young adults, and may also indicate thymic hyperplasia in patients after chemotherapy or with Graves' disease. F-18 FDG PET-CT proves to be effective in differentiating thymic carcinoma from other entities within the thymus, and thymoma from thymic hyperplasia. The intensity of FDG uptake is useful for predicting the grade of malignancy in thymic epithelial tumors. However, the literature is equivocal with regard to the ability of F-18 FDG PET-CT to differentiate between invasive and noninvasive thymomas. Further larger studies are required to clarify the effectiveness and explore more clinical implications of F-18 FDG PET-CT on thymic lesions.     

18F-FDG PET/CT of thymic epithelial tumors: usefulness for distinguishing and staging tumor subgroups.

The purpose of our study was to assess the usefulness of integrated PET/CT using 18F-FDG for distinguishing thymic epithelial tumors according to the World Health Organization (WHO) classification. METHODS: Thirty-three patients (age range, 34-68 y; mean age, 54.6 y) with thymic epithelial tumors, who underwent both integrated PET/CT and enhanced CT, were included. The clinicopathologic stages, maximum standardized uptake values (SUVs), and uptake patterns of tumors on integrated PET/CT images, and various enhanced CT findings, are described according to the simplified (low-risk [types A, AB, and B1] and high-risk [types B2 and B3] thymomas and thymic carcinomas) subgroups of the WHO classification. Discriminant analysis was performed to determine the relative capabilities of integrated PET/CT and enhanced CT findings to differentiate tumor subgroups. RESULTS: Tumors included 8 low-risk thymomas, 9 high-risk thymomas, and 16 thymic carcinomas. The maximum SUVs of high-risk thymomas (P < 0.001) and low-risk thymomas (P < 0.001) were found to be significantly lower than those of thymic carcinomas. Homogeneous 18F-FDG uptake within tumors was more frequently seen in thymic carcinomas than in high-risk thymomas (P = 0.027) or low-risk thymomas (P = 0.001). The uptake pattern (homogeneous vs. heterogeneous) on integrated PET/CT images and the presence of mediastinal fat invasion on enhanced CT images were found to be useful for differentiating tumor subgroups. In addition, integrated PET/CT helped detect lymph node metastases, which were not identified on enhanced CT in 2 patients. CONCLUSION: Integrated PET/CT was found to be useful for differentiating subgroups of thymic epithelial tumors and for staging the extent of the disease.     

The thymus gland in computerized tomography. Normal findings and pathology

The diagnostic value of CT in follicular thymic hyperplasia and in thymomas in 8 patients with myasthenia gravis and in 12 patients without myasthenia gravis suffering from thymic tumors was evaluated by correlating CT-findings to surgical results and pathological-histological findings. Thymic size of the six patients with histologically proven follicular hyperplasia were scattered within the normal range, but half of them were at the upper limit. Thymic tumors were differentiated between invasive and non invasive tumors by CT staging. Solid tumors with different histology could not be further classified; the attenuation values ranging from 15-55 HU were the same in tumors, follicular hyperplasia and normal thymus.     

Thymic epithelial tumors: comparison of CT and MR imaging findings of low-risk thymomas, high-risk thymomas, and thymic carcinomas

OBJECTIVE: To assess the CT and magnetic resonance (MR) imaging findings of thymic epithelial tumors classified according to the current World Health Organization (WHO) histologic classification and to determine useful findings in differentiating the main subtypes. MATERIALS AND METHODS: Sixty patients with thymic epithelial tumor who underwent both CT and MR imaging were reviewed retrospectively. All cases were classified according to the 2004 WHO classification. The following findings were assessed in each case on both CT and MRI: size of tumor, contour, perimeter of capsule; homogeneity, presence of septum, hemorrhage, necrotic or cystic component within tumor; presence of mediastinal lymphadenopathy, pleural effusion, and great vessel invasion. These imaging characteristics of 30 low-risk thymomas (4 type A, 12 type AB, and 14 type B1), 18 high-risk thymomas (11 type B2 and seven type B3), and 12 thymic carcinomas on CT and MR imaging were compared using the chi-square test. Comparison between CT and MR findings was performed by using McNemar test. RESULTS: On both CT and MR imaging, thymic carcinomas were more likely to have irregular contours (P < .001), necrotic or cystic component (P < .05), heterogeneous contrast-enhancement (P < .05), lymphadenopathy (P < .0001), and great vessel invasion (P < .001) than low-risk and high-risk thymomas. On MR imaging, the findings of almost complete capsule, septum, and homogenous enhancement were more commonly seen in low-risk thymomas than high-risk thymomas and thymic carcinomas (P < .05). MR imaging was superior to CT in the depiction of capsule, septum, or hemorrhage within tumor (all comparison, P < .05). CONCLUSION: The presence of irregular contour, necrotic or cystic component, heterogeneous enhancement, lymphadenopathy, and great vessel invasion on CT or MR imaging are strongly suggestive of thymic carcinomas. On MR imaging, the findings of contour, capsule, septum, and homogenous enhancement are helpful in distinguishing low-risk thymomas from high-risk thymomas and thymic carcinomas.     

Mediastinal imaging in myasthenia gravis: correlation of chest radiography, CT, MR, and surgical findings

Chest radiographs and CT and MR images of the mediastinum were studied in 16 patients with myasthenia gravis who underwent thymectomy (two with a final diagnosis of thymoma, seven with hyperplasia, and seven with a normal thymus). The anterior mediastinum was analyzed on imaging studies for thymic morphology and the presence of mass lesions, and the findings were then correlated with the results of surgical resection and pathologic examination. The chest radiographs detected an anterior mediastinal mass in two patients consistent with thymoma on subsequent CT and MR examinations. Chest radiographs in the other 14 patients were normal. In seven patients with a final diagnosis of thymic hyperplasia, both CT and MR demonstrated normal thymic morphology in five, an enlarged thymus in one, and a small thymus in one that was easily identified on CT but was difficult to define on MR. In the other seven patients with a normal thymus on pathologic examination, both CT and MR showed an involuted thymus in four, a normal thymus in two, and an enlarged thymus in one. While both CT and MR were superior to chest radiography for studying the thymus, CT provided better spatial resolution and thymic definition in a much shorter scanning time than MR did. This study suggests that CT should remain the procedure of choice when further imaging of the thymus is needed after the initial chest radiographs in patients with myasthenia gravis.     

MR imaging of thymoma--comparison with CT, operative, and pathological findings]

Twenty-six patients with thymoma, who had magnetic resonance (MR) imaging and computed tomography (CT) before surgery, were studied. Twenty-six thymomas were classified into 11 non-invasive thymomas (Masaoka's clinical stage I) and 15 invasive thymomas (stage II, III, and IV). On MR imaging compared with histological findings, low signal intensity rim of the tumor was corresponded to fibrous capsule of the tumor, and linear and/or reticular low signal intensity lines in the tumor were corresponded to the fibrous septae dividing thymoma into lobules. The detectability of these findings by MR imaging was superior to that by CT. Margin of the tumor was smooth in non-invasive thymoma rather than invasive thymoma. The diagnostic accuracy of invasion to vessel, and pleura or lung on MR imaging and CT was compared with operative and histological findings. MR imaging was same as CT in its ability to detect tumoral invasion to vessel, and slightly superior to pleura or lung. In conclusion MR images clearly show the findings corresponding to pathologic specimens, and MR imaging combining with CT is useful to differentiate non-invasive thymoma to invasive thymoma.     

Thymic lesions and myasthenia gravis. Diagnosis based on mediastinal imaging and pathological findings

Purpose:
To achieve a better understanding of the role of CT and MR imaging in the study of the mediastinum in patients with myasthenia gravis (MG). Material and Methods:
Mediastinal CT and MR findings were correlated with the histopathological results in 104 thymectomized MG patients. Results:
CT was performed in 104 patients; in 11 of them, MR was also carried out. 44 patients had hyperplasia at histology. On CT, thymic hyperplasia was confirmed in 16 cases, thymoma was diagnosed in 10 and a normal thymus in 18 (sensitivity 36%, specificity 95%). Of 52 patients with thymoma at histology, CT showed thymoma in 46, hyperplasia in 1, and normal thymus in 5. CT showed 88.5% sensitivity and 77% specificity for thymoma. In 10 patients with invasive thymoma, CT was indiscriminate, while invasiveness was detected in 7 cases at MR (70% sensitivity) and at CT in 1 case. Both CT and MR detected tumor recurrence in 5 cases, but the exact localization and degree of invasion were best defined by MR. Conclusion:
In MG patients CT is a sensitive, specific and efficient modality for detecting thymoma, but is less so for detecting thymic hyperplasia. MR was shown to be accurate in detecting invasive thymoma both preoperatively and in postoperative follow-up.     

Thymic masses on MR imaging

MR imaging is an excellent technique for identifying and defining the extent of thymic tumors. T1-weighted spin-echo MR images (e.g., 600/15 [TR/TE]) best demonstrate tumor extent, and T2-weighted images (e.g., 2500/90 [TR/TE]) help differentiate "cystic" from solid thymic masses. Cyst formation and/or hemorrhage appear as areas of high signal intensity (greater than that of fat) on T2-weighted images. Focal areas of low signal intensity (less than that of muscle) correspond pathologically to fibrous capsules and septa, air, or calcification. In this report, the MR appearance of the normal thymus is reviewed briefly, and the gamut of abnormal thymic masses on MR is illustrated.     

MR imaging in thyroid disorders: correlation of signal intensity with Graves disease activity

Thirty-six patients with a variety of thyroid disorders and eight healthy subjects were studied with T1- and T2-weighted magnetic resonance (MR) imaging. Solid benign nodules, malignant tumors, and inflammatory conditions were not distinguishable by thyroidal MR signal intensity, but almost all patients with Graves disease had a moderate to marked diffuse increase in signal intensity at both settings. Quantitative evaluation showed that in these patients, the thyroid-muscle signal intensity contrast ratio was linearly related to both the serum thyroxine (T4) level and the 24-hour radioactive iodine uptake. In three patients treated with iodine 131, this contrast ratio rose or fell in parallel with the serum T4 level and 24-hour radioactive iodine uptake. Either parenchymal changes or increased vascularity in Graves disease, or both, could produce these findings. In patients without Graves disease, signal intensity was not correlated with serum T4 levels. These findings suggest that MR signal intensity may reflect the activity of the stimulatory process in Graves disease and may therefore be a useful measure of thyroid function in this disorder, with both diagnostic and prognostic value.     

Thymic hyperplasia after high-dose chemotherapy and autologous stem cell transplantation: incidence and significance in patients with breast cancer.

OBJECTIVE: The purpose of this study was to determine the incidence and clinical significance of thymic hyperplasia after high-dose chemotherapy and autologous stem cell transplantation for treatment of metastatic or high-risk primary (with at least four positive lymph nodes) breast cancer. MATERIALS AND METHODS: We retrospectively reviewed clinical records and CT scans of 102 breast cancer patients treated with high-dose chemotherapy and autologous stem cell transplantation. Patients were 26-63 years old (mean, 46 years). The length and width of the thymus gland were measured on serial CT scans obtained before and after treatment. Moderate thymic hyperplasia was recorded if a focal or diffuse increase was seen in the oblong, triangular soft-tissue opacity conforming to the configuration of the normal gland within the anterior mediastinum after therapy. Minimal hyperplasia was recorded when a minimal increase was seen in soft-tissue attenuation conforming to the configuration of the normal bilobed thymus gland within the anterior mediastinum, but no discrete mass was visible. RESULTS: CT showed no thymic hyperplasia in 91 (89%) of the 102 patients. CT showed thymic hyperplasia in the other 11 patients (11%). Three patients (3%) had moderate hyperplasia, and eight patients (8%) had minimal hyperplasia. When comparing patients with and without hyperplasia, we found no difference in mean age or survival. CONCLUSION: Thymic hyperplasia is rare after high-dose chemotherapy and autologous stem cell transplantation in adult patients with metastatic or high-risk primary breast cancer. In this population, thymic hyperplasia does not appear to correlate with survival.     

Characterization of the normal and hyperplastic thymus on chemical-shift MR imaging

OBJECTIVE: We designed our study to prospectively assess a potential role for chemical-shift MR imaging in identifying a thymus that has not been completely replaced by fat tissue. CONCLUSION: The thymic tissue revealed homogeneous decrease in intensity on opposed-phase MR images relative to that seen on in-phase images in 15 healthy volunteers and two patients with hyperplastic thymus. Chemical-shift MR imaging may be useful in identifying normal thymic tissue and the hyperplastic thymus in early adulthood.     

Dynamic contrast-enhanced T2*-weighted MR imaging of gliomatosis cerebri

BACKGROUND AND PURPOSE: MR imaging characteristics of gliomatosis cerebri reiterate the diffuse nature of this tumor but are nonspecific and thus may pose a diagnostic challenge. Because perfusion MR imaging can provide a physiologic map of the microcirculation, we compared the measured relative cerebral blood volume (rCBV) at perfusion imaging with histopathologic findings in gliomatosis cerebri. MR spectroscopic findings were also reviewed. METHODS: Retrospective analysis was performed of conventional and perfusion MR images from seven patients with proved gliomatosis cerebri. The conventional MR images were evaluated for the presence or absence of contrast enhancement, necrosis, and extent of T2-weighted signal intensity abnormality. Dynamic contrast-enhanced T2*-weighted gradient-echo echo-planar images were acquired during the first pass of a bolus injection of gadopentetate dimeglumine. The rCBV was calculated by using nondiffusible tracer kinetics and expressed relative to normal-appearing white matter. Pathologic findings were reviewed in all patients and compared with the MR perfusion data. Multivoxel 2D chemical shift imaging proton MR spectroscopic data were available for three patients and single-voxel data for one patient. RESULTS: Conventional MR images showed diffuse abnormality in all cases and absence of contrast enhancement in all but one case. Average rCBV range was 0.75-1.26 (mean, 1.02 +/- 0.42 [SD]). MR spectroscopic data revealed spectra consistent with presence of tumoral disease. Histopathologic review showed absence of vascular hyperplasia in all specimens. CONCLUSION: The low MR rCBV measurements of gliomatosis cerebri are in concordance with the lack of vascular hyperplasia found at histopathologic examination; thus, perfusion MR imaging provides useful adjunctive information that is not available from conventional MR imaging techniques.     

Use of fluorine-18 fluorodeoxyglucose positron emission tomography in the detection of thymoma: A preliminary report

Thymomas are lacking in malignant cytological features. Their staging is defined by the invasiveness of the tumour. This study aimed to analyse the uptake patterns of fluorine-18 fluorodeoxyglucose (FDG) in thymomas of different stages. FDG positron emission tomography (PET) scan was performed in 12 patients suspected of having thymoma and in nine controls. Qualitative visual interpretation was used to detect the foci with FDG uptake higher than that of normal mediastinum. Tumour/lung ratio (TLR) was calculated from the counts of ROIs over the mass and over comparable normal lung tissue in thymoma patients. Mediastinum/lung ratio (MLR) was calculated from the counts of ROIs over the anterior mediastinum and lung in controls. The PET scan patterns of distribution of foci with FDG uptake and TLRs were correlated with the computed tomography (CT) or magnetic resonance imaging (MRI) findings, and staging of the thymomas. Thymectomy was performed in ten patients and thoracoscopy was done in two patients. The results revealed ten thymomas (two stage I tumours, two stage II, four stage III and two stage IV, according to the Masaoka classification), and two cases of thymic hyperplasia associated with myasthenia gravis. Myasthenia gravis was also noted in four thymoma patients. FDG studies showed (a) diffuse uptake in the widened anterior mediastinum in patients with thymic hyperplasia, (b) confined focal FDG uptake in the non-invasive or less invasive, stage I and II thymomas, and (c) multiple discrete foci of FDG uptake in the mediastinum and thoracic structures in stage III and IV advanced invasive thymomas. The thymomas had the highest TLRs, followed by the TLRs of thymic hyperplasia and the MLRs of control subjects (P <0.005). No significant difference was found between thymomas in different stages or between thymomas with and thymomas without myasthenia gravis. In comparison with CT and/or MRI, FDG-PET detected more lesions in patients with invasive thymomas and downgraded the staging of thymoma in four patients. Our preliminary results suggest that FDG-PET is useful in the assessment of the invasiveness of thymomas, and may have the potential to differentiate thymomas from thymic hyperplasia.     

Renal angiomyolipoma with minimal fat: differentiation from other neoplasms at double-echo chemical shift FLASH MR imaging

PURPOSE: To prospectively evaluate the diagnostic performance of double-echo gradient-echo (GRE) chemical shift magnetic resonance (MR) imaging in the differentiation of angiomyolipoma (AML) with minimal fat from other renal neoplasms, with pathologic examination or follow-up data serving as the reference standard. MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained. Double-echo GRE chemical shift MR imaging was performed in 55 patients (29 men and 26 women; mean age, 49 years +/- 14 [standard deviation]) with 55 renal tumors, including 37 (67%) pathologically proved tumors (23 renal cell carcinomas, nine AMLs, two oncocytomas, two lymphomas, and one reninoma) and 18 (33%) clinically diagnosed tumors (17 AMLs and one indeterminate malignancy). All tumors showed no intratumoral fat and had homogeneous enhancement and a prolonged or gradual enhancement pattern on biphasic helical computed tomographic scans. Signal intensity was measured in the renal tumor and spleen on in-phase and opposed-phase images. The signal intensity index and tumor-to-spleen ratio in AMLs and non-AMLs were calculated and compared with the Student t test. Receiver operating characteristic (ROC) analysis was performed to evaluate the diagnostic accuracy of the signal intensity index and tumor-to-spleen ratio and to extract the optimal cut-off values in the differentiation of AMLs and non-AMLs. RESULTS: The signal intensity index and tumor-to-spleen ratio were different between AMLs (42% +/- 11 and -43% +/- 17, respectively) and non-AMLs (5% +/- 14 and -4% +/- 16, respectively) (P < .001). The area under the ROC curve was 0.975 for the signal intensity index and 0.952 for the tumor-to-spleen ratio. For differentiation of AMLs from non-AMLs, sensitivity and specificity were (a) 96% and 93%, respectively, with a signal intensity index of 25% and (b) 88% and 97%, respectively, with a tumor-to-spleen ratio of -32%. CONCLUSION: Double-echo GRE chemical shift MR imaging can be used to differentiate AML with minimal fat from other renal neoplasms.     

Magnetic resonance of the prostate: critical evaluation of diagnostic possibilities

The authors retrospectively reviewed 140 MR examinations of the prostate to assess the presence of similar findings in the different patients affected with the same prostatic disease. In 35 patients with acute phlogosis, MR imaging showed enlargement of peripheral gland, with increased signal intensity on T2-weighted images, while reduced peripheral gland with low signal intensity was demonstrated in chronic phlogosis. Five patients presented roundish cystic lesions, with clear-cut outlines, clearly distinguishable from the surrounding parenchyma. Benign Prostatic Hyperplasia (BPH) was observed in 32 cases. 52% of them had multiple nodules with high signal intensity, 40% had hyperintense enlarged central glands, with no evidence of BPH nodules, and the remaining 8% presented single/multiple nodules with low signal intensity. In 56 patients with prostatic carcinoma the tumor extent ranged from 18-20 mm nodules to 5-6 cm masses with involvement of periprostatic adipose tissue or surrounding organs. The smallest lesions were always found in the peripheral gland and had low signal intensity on T2-weighted sequences. In spite of the different findings in the patients affected with BPH, the study proved MR imaging to be able to distinguish the various patterns of the different prostatic diseases.     

Characterization of focal hepatic lesions with ferumoxides-enhanced T2-weighted MR imaging

OBJECTIVE: The purpose of this study was to evaluate whether ferumoxides-enhanced MR imaging of focal hepatic lesions provides distinctive signal intensity and lesion-to-liver contrast changes for benign and malignant lesions, helping to further characterize and differentiate these lesions. MATERIALS AND METHODS: Data analysis was performed on 70 patients, with previously identified focal hepatic lesions, who underwent MR imaging of the liver before and after IV administration of ferumoxides (10 micromol Fe/kg). Lesions analyzed with pathologically proven diagnoses included metastases (n = 40), hepatocellular carcinoma (n = 11), cholangiocarcinoma (n = 6), hemangioma (n = 4), focal nodular hyperplasia (n = 6), and hepatocellular adenoma (n = 3). Response variables measured and statistically compared included the percentage of signal-intensity change and lesion-to-liver contrast. RESULTS: Focal nodular hyperplasia showed significant signal intensity loss on ferumoxides-enhanced T2-weighted images (mean, -43%+/-6.7%, p < 0.01). All other lesion groups showed no statistically significant change in signal intensity on ferumoxides-enhanced T2-weighted images, although signal intensity loss was seen in some individual hepatocellular adenomas (mean, -6.6%+/-24.0%) and hepatocellular carcinomas (mean, -3.3%+/-10.3%). All lesions, with the exception of hepatocellular carcinoma, had a marked increase in lesion-to-liver contrast on ferumoxides-enhanced T2-weighted images, which was statistically significant for metastases and hemangioma (p < 0.02). CONCLUSION: Focal nodular hyperplasia shows significant decrease in signal intensity on ferumoxides-enhanced T2-weighted images, which may aid in the differentiation of focal nodular hyperplasia from other focal hepatic lesions. Other lesions, namely, hepatocellular adenoma and carcinoma, can have reticuloendothelial uptake, but usually to a lesser degree than that of focal nodular hyperplasia.     

MR of cystic aberrant cervical thymus.

The clinical, MR imaging, surgical, and histologic findings in two cases of cystic aberrant cervical thymus were reviewed. Aberrant cervical thymic tissue was sharply circumscribed and extended deep to the posterior pharyngeal wall at the level of the piriform sinus in both cases. Both lesions had cyst contents that were of increased signal intensity on T1-weighted images. Solid components displayed MR signal characteristics identical to normal thymus.