MR appearance of the pseudocapsule of renal cell carcinoma and its pathologic basis

The pseudocapsule of renal cell carcinoma (RCC) appears as a low-intensity band or rim on magnetic resonance (MR) images. The frequency of its appearance differed on T1- and T2-weighted images. In our group of 19 RCC (in 18 patients), it appeared on 26.3% of T1-weighted images and on 57% of T2-weighted images. The pathology of the pseudocapsule on MR is its thickness and composition. On T1-weighted images, the appearance of the pseudocapsule is mainly related to the fibrous element, and on T2-weighted images to the fibrous element and compressed renal parenchyma.     

Significance of the pseudocapsule on MRI of renal neoplasms and its potential application for local staging: a retrospective study

OBJECTIVE: The purpose of our study was to evaluate the role of MRI in showing a pseudocapsule for local staging of renal tumors, and its potential application to select patients for partial surgery. MATERIALS AND METHODS: Eighty tumors (73 renal cell carcinomas [RCCs] and seven oncocytomas) were preoperatively evaluated by MRI. MRI findings were assessed with a special focus on perinephric fat and pseudocapsule. Correlations were performed with pathologic staging after surgery. RESULTS: At pathology, a pseudocapsule was recognized in 79 cases. Twenty-three RCC were staged pT3a (21 clear cell; two papillary). MR images exhibited a pseudocapsule in 90% of cases as a hypointense rim surrounding the tumor on T2-weighted images. MRI findings concerning isolated analysis of the pseudocapsule for differentiating stage T1/T2 from T3a were sensitivity: 86%, 50%; specificity: 95%, 92%; positive predictive value: 95%, 33%; negative predictive value: 88%, 92%; and accuracy: 93%, 89%, for clear cell and papillary types, respectively. For stage T3a, with both abnormalities of the pseudocapsule and perirenal fat, results were, for overall RCC sensitivity: 84%; specificity: 95%; positive predictive value: 91%; negative predictive value: 91%; and accuracy: 91%. CONCLUSION: The identification of the pseudocapsule offers an additional value for local staging by MRI. The presence of an intact pseudocapsule is a sign of lack of perinephric fat invasion. It is more likely to predict that the tumor can be removed by partial surgery.     

Telangiectatic focal nodular hyperplasia: US,CT, and MR imaging findings with histopathologic correlation in 13 cases

PURPOSE: To review the ultrasonographic (US), computed tomographic (CT), and magnetic resonance (MR) imaging findings in 13 patients with telangiectatic focal nodular hyperplasia (FNH) and to compare imaging features with histopathologic results from resected specimens. MATERIALS AND METHODS: US, helical multiphasic CT, and MR images in 13 patients with pathologically proven telangiectatic FNH were reviewed retrospectively. Two abdominal radiologists evaluated lesions for number, size, heterogeneity, surface characteristics, presence of a central scar, presence of a pseudocapsule, US appearance, attenuation at CT, signal intensity at MR imaging, and presence of associated lesions. Imaging and pathologic findings were compared. RESULTS: Sixty-one lesions (5-140 mm in diameter) were seen at imaging. Lesions were multiple in eight of 13 (62%) patients. Imaging characteristics were heterogeneity in 26 of 61 lesions (43%), well-defined margins in 43 of 61 (70%), lack of a central scar in 56 of 61 (92%), presence of a pseudocapsule in three of 61 (5%), hyperintensity on T1-weighted MR images in 17 of 32 (53%), strong hyperintensity on T2-weighted MR images in 24 of 54 (44%), and persistent enhancement on delayed contrast material-enhanced CT or T1-weighted MR images in 23 of 38 (61%). No specific US pattern was noted. Two patients had additional lesions: One had classic FNH, and the other had a cavernous hemangioma. Hyperintensity on T1-weighted MR images was due to sinusoidal dilatation. Hyperintensity on T2-weighted MR images correlated well with the presence of inflammation. CONCLUSION: Telangiectatic FNH differs from typical FNH at imaging: Atypical FNH features often observed with telangiectatic FNH are lack of a central scar, lesion heterogeneity, hyperintensity on T1-weighted MR images, strong hyperintensity on T2-weighted MR images, and persistent contrast enhancement on delayed contrast-enhanced CT or T1-weighted MR images.     

Focal nodular hyperplasia of the liver: MR imaging and pathologic correlation in 37 patients.

Thirty-seven patients with 48 lesions of focal nodular hyperplasia (FNH) underwent preoperative magnetic resonance (MR) examination and surgical resection. Sixteen lesions were imaged at 0.5 T with T1- and T2-weighted spin-echo sequences; 32 lesions were imaged at 2 T with T1-and T2-weighted spin-echo and gradient-recalled-echo sequences. Contrast material-enhanced MR imaging was performed in 20 lesions. MR imaging failed to depict six tumors that were less than 3 cm in diameter. Typical appearance was present in 18 of the 42 (43%) lesions seen at MR. Atypical lesion features included no scar (n = 15), hypointense scar on T2-weighted images (n = 7), pseudocapsule (n = 6), strong hyperintense lesion on T2-weighted images (n = 3), diffuse hyperintensity on T1-weighted images (n = 3), and heterogeneous lesion (n = 1). Comparison between findings at MR imaging and at histopathologic examination was performed in 38 lesions: There was good correlation between presence and size of the scar on both examinations. In 13 of 20 (65%) of the hyperintense scars on T2-weighted images, edema was prominent, whereas in five of the seven (71%) hypointense scars on T2-weighted images, edema was absent or low.     

MR imaging of neurilemoma arising from the renal hilus

The authors present the radiologic findings of a neurilemoma arising from the kidney. Ultrasound, CT, and angiography could not exclude the diagnosis of renal cell carcinoma (RCC). Magnetic resonance (MR) imaging at 1.5 T showed an isointense tumor on T1-weighted images and a high signal intensity on T2-weighted images compared with normal renal parenchyma. The MR findings were helpful in the differentiation from RCC.     

Uterine leiomyoma: correlation between signal intensity on magnetic resonance imaging and pathologic characteristics.

To correlate the signal intensity of uterine leiomyoma with its pathologic characteristics, with particular emphasis on the fibrous component, 33 magnetic resonance (MR) examinations that revealed 93 leiomyomas were prospectively studied. All patients were imaged in axial and sagittal planes with different spin-echo pulse sequences to obtain T1-, T2-weighted, and proton density images. Nondegenerative leiomyomas (n = 62) showing a homogeneous signal of low intensity, and degenerative leiomyomas (n = 31) with a heterogeneous signal of variable intensity on T2-weighted images could be correlated. Histopathological assessment of fiber constitution and degeneration, and MR intensity were interpreted by independent observers. There was excellent accord between the averages for MR intensity, T2 relaxation time and fiber content, although the intensity values in each fiber grade showed a wide range. The greater the fiber content the lower the MR intensity on T2-weighted images, and the shorter the T2 relaxation time (p < 0.0001). In addition, the manner in which fiber distribution affected MR appearance was also elucidated. These data contribute guidelines for precise tissue differentiation of myogenic tumors on MR images, and for MR imaging tissue diagnosis of any lesion with a considerable fibrous element.     

MR imaging follow-up after percutaneous radiofrequency ablation of renal cell carcinoma: findings in 18 patients during first 6 months

PURPOSE: To prospectively evaluate the magnetic resonance (MR) imaging findings seen within the first 6 months after radiofrequency (RF) thermal ablation of renal cell carcinoma (RCC). MATERIALS AND METHODS: After providing written informed consent, 18 patients (17 men, one woman; mean age, 71.2 years) with RCC underwent MR imaging-guided percutaneous RF thermal ablation, which was performed by using protocols approved by a comprehensive cancer center protocol committee and the institutional review board for human investigation. The study was Health Insurance Portability and Accountability Act compliant. Follow-up unenhanced T2-weighted MR images and unenhanced and gadolinium-enhanced T1-weighted MR images were acquired immediately, 2 weeks, 3 months, and 6 months after ablation. Thermal ablation zone size was analyzed, and contrast-to-noise ratios (CNRs) were calculated from the signal amplitudes of the thermal ablation zone, perirenal fat, and normal renal cortex on the MR images. Statistical analyses were performed by using the paired Student t test. P < .05 was considered to indicate statistical significance. RESULTS: The mean follow-up time was 16.1 months (range, 6.0-41.2 months). The mean sizes of the thermal ablation zones were 6.8, 7.0, 6.1, and 4.7 cm2, respectively, at immediate, 2-week, 3-month, and 6-month follow-up MR imaging examinations. Thermal ablation zones were uniformly hypointense and had a surrounding bright rim on T2-weighted images and were predominantly hyperintense on T1-weighted images. Thin rim enhancement with central hypointensity was noted on the gadolinium-enhanced images. Gadolinium-enhanced T1-weighted and unenhanced T2-weighted MR images showed significantly higher CNRs than unenhanced T1-weighted MR images. Residual tumor was detected after RF thermal ablation in two cases and was best seen on unenhanced T2-weighted and gadolinium-enhanced T1-weighted MR images. CONCLUSION: After initially increasing in size within the first 2 weeks, renal RF thermal ablation zones involuted during the remainder of the MR imaging follow-up period.     

The pseudocapsule in hepatocellular carcinoma: correlation between dynamic MR imaging and pathology

Nodular hepatocellular carcinoma (HCC) is characterized by the presence of a pseudocapsule (constructed usually from connective fibrous tissue) that appears hypointense on T1- and T2-weighted spin-echo (SE) and gradient-echo (GE) MR imaging sequences without a contrast medium. The presence of vascular structures inside the tumor, which are verified by histological exam, affects enhancement of the PC after administrating the contrast medium: The impregnation is more evident in the dynamic study but also persists on the delayed T1-weighted SE images. The accuracy of MR in detecting the pseudocapsule of HCC and contrast enhancement of the pseudocapsule during dynamic studies were evaluated and related to pathological findings. Thirty-seven HCC were examined in 33 patients and afterwards resected. In capsulated nodules, besides usual hematoxylin, eosin, and trichrome stainings, histochemical and immunohistochemical methods were performed. On a 1.5-T MR unit, T1- and T2-weighted SE and GE FLASH 2D sequences after intravenous injection of Gd-DTPA (dynamic study) were used. In a later phase, T1-weighted SE sequences were repeated. Histologically, the pseudocapsule (thickness 0.2–6 mm) was present in 26 of 37 nodules (70 %). The dynamic study was the most suitable technique to show the pseudocapsule, which was recognized in 80.7 % (21 of 26 nodules). In 5 of 26 cases, the pseudocapsule, not demonstrated by MR, was thinner than 0.4 mm. In 16 of 21 cases, in the early portal phase (30–60 s), the pseudocapsule had an early enhancement, which was more evident later; in 5 of 21 cases the enhancement was observed only in the late portal phase (1–2 min). At histological examination, 14 of 16 pseudocapsules with early enhancement showed a more prominent vasculature than those with enhancement in the equilibrium phase. Magnetic resonance was a reliable tool in demonstrating the pseudocapsule of HCC. The histological examination demonstrated a good correlation between the enhancement behavior and the vessel number of the pseudocapsule. Received: 28 July 1997; Revision received: 9 February 1998; Accepted: 20 March 1998     

Human peripheral arteries: feasibility of transvenous intravascular MR imaging of the arterial wall

Feasibility of in vivo transvenous intravascular magnetic resonance (MR) imaging of the human arterial wall was determined. All subjects provided written informed consent, and institutional review board approved the study. Six arteries in six patients were imaged with a guidewire placed in the iliac vein (n = 5) or left renal vein (n = 1). Pre- and postcontrast T1-weighted and T2-weighted transvenous MR imaging were performed. An atherosclerotic plaque with a fibrous cap was identified on 27 (42%) of 64 images of veins without stents; intimal hyperplasia in a renal artery with a stent was identified on 12 images. Contrast-to-noise ratios (CNRs) on arterial wall postcontrast T1-weighted images were superior to those on images obtained with other sequences (P < .001), and the postcontrast images demonstrated the greatest number of plaques with a low-signal intensity core and fibrous cap. Preliminary results show that transvenous MR imaging is feasible for high-spatial-resolution imaging of the arterial wall and atherosclerotic plaque. Postcontrast T1-weighted imaging affords greatest CNR for the arterial wall.     

Endometrial cysts of the ovary: MR imaging

Magnetic resonance (MR) images of 15 cases of ovarian endometrial cyst were reviewed. With a high-field-strength (1.5-T) MR imager, T1- and T2-weighted images were obtained in axial and sagittal planes, with 5-mm section thickness. MR findings highly suggestive of an endometrial cyst included adhesions to the surrounding organs (e.g., loss of clear margin of the uterine body and tethered appearance of the rectum); a distinct low-intensity zone surrounding a cyst loculus on both T1- and T2-weighted images produced by a thick fibrous capsule; loculus contents with short T1 and long T2 values, attributed to hemorrhagic fluid; and prominent low intensity (shading) within a loculus on T2-weighted images, the mechanism of which is yet to be determined.     

MR appearance of fibrous dysplasia

Magnetic resonance (MR) imaging is utilized in diverse clinical circumstances for evaluation of the musculoskeletal system. Consequently, common benign skeletal lesions may be detected incidentally following MR scan obtained for unrelated reasons. The spectrum of MR appearances of fibrous dysplasia has not been previously reported. We retrospectively reviewed all radiologic images (including the MR scans) of 11 sites of fibrous dysplasia encountered in seven patients. On MR, the fibrous dysplastic lesion causes an "expanded" bony contour and is characterized by decreased signal on T1-weighted image. The signal on T2-weighted MR scan is variable, however. Since fibrous dysplasia is a (relatively) common skeletal lesion that can be encountered incidentally, all radiologists should be familiar with its MR appearance. Furthermore, in the unlikely possibility of surgical intervention, MR is useful in determining the extent of disease within the affected bone and planning the preoperative strategy.     

子宫肌瘤的MR成像研究以--DSA为参照

目的 以DSA为参照评价子宫肌瘤的MRI表现。资料与方法 对DSA上有明显血供的子宫肌瘤行MRI检查,所有病例采用SE T1、turbo—SE T2WI和SET1WI增强扫描,对比剂为Gd—DTPA,剂量0．1mmol／kg体重,对不同成像序列的MRI信号特点和相关征象进行分析。结果 37个肌瘤T1WI均表现为等、低信号T2WI多为等、高信号(28个肌瘤),增强扫描肌瘤均出现明显强化,信号多数高于或等于子宫肌层(35个肌瘤)。多数肌瘤内部为均匀结节状或团块状改变,其间可见分隔结构,肌瘤包膜在T1WI、T1WI和增强扫描时能明确显示。结论 DSA表现明显血供的子宫肌瘤MRI有一定的特征性表现,增强扫描能够较为准确地反映肌瘤血供。     

Small renal cell carcinoma: MRI with pathologic correlation

The MRI features of small renal cell carcinomas (RCCs) were retrospectively reviewed and correlated with histology in 24 patients. MRI features on both T1- and T2-weighted images were classified into hypointensity, isointensity, and hyperintensity. Each tumor was pathologically classified into four types: alveolar, papillary, tubular, and cystic. These findings were correlated with MR signal intensities. Alveolar tumors showed hypointensity to isointensity on T1-weighted image and isointensity to hyperintensity on T2-weighted image. In contrast, all papillary tumors showed hypointensity on T2-weighted image. Four of six tumors with hypointensity on T2-weighted image were caused by hemosiderin deposition, hemorrhage, and necrosis. However, there were two papillary RCCs that showed hypointensity on T2-weighted image despite no hemosiderin deposition and no hemorrhage. We conclude that papillary RCC is associated with T2-hypointense appearance as well as hemosiderin deposition, hemorrhage, and necrosis.     

MR imaging in retinoblastoma

We studied the appearance of retinoblastoma on unenhanced and gadolinium-enhanced images and the accuracy of tumour staging with MR imaging. The MR images were obtained in 18 children with retinoblastoma and compared with histopathological findings after enucleation. The MR imaging included T1-weighted and dual-echo T2-weighted images before, and T1-weighted images after, gadopentetate dimeglumine injection. The contrast between tumour and ipsilateral vitreous strongly increased (57%) after gadolinium on T1-weighted images (p=0.004). Tumour was strongly hypointense as compared with ipsilateral vitreous in all patients using heavily T2-weighted (TE=120 ms) images (p=0.001). The estimated T2 of tumour (mean 96+14 ms) did not correlate with histological grading or degree of calcification. Unenhanced T1-weighted MR images rightfully excluded extrascleral growth in 16 of 16 cases, but its presence was confirmed after enucleation in only one of 2 abnormal MR scans. Invasion of the optic nerve behind the cribriform plate was confirmed in 2 of 3 abnormal gadolinium-enhanced MR scans, but also in 1 of the 15 cases in which MR images were normal. The T2-weighted images were useful in assessing retinal detachment. We conclude that heavily T2-weighted images, unenhanced T1-weighted images and gadolinium-enhanced T1-weighted MR images are complementary in characterizing and staging retinoblastoma.     

A left atrial pseudomass: Potential pitfall at thoracic MR imaging

We frequently observed a nodular soft-tissue structure in the region of the left atrium anterior to the orifice of the left inferior pulmonary vein on MR scans of the chest. To assess its morphologic characteristics and appearance, chest MR scans obtained in 49 patients were reviewed. ECG-gated conventional spin-echo T1-weighted and fast spin-echo (FSE) T2-weighted sequences were used. The location, morphology, and appearance of this soft-tissue structure was evaluated by two radiologists during one consensus reading. The psendomass in the region of the left atrium was identified on the T1-weighted images in 25 of 49 patients. The structure was also identified on FSE T2-weighted images in 6 of these patients. On the T1-weighted images, its appearance was either linear (54%) or nodular (46%). In conclusion, a nodular soft-tissue mass anterior to the orifice of the left inferior pulmonary vein into the left atrium is a frequent finding on chest MR scans and should not be confused with an intra-atrial mass. Careful evaluation of the regional anatomy identifies this structure as extraluminal and helps to avoid misinterpretation of an intracardiac mass.     

Curvilinear areas in the perinephric fat seen on MR images.

AIM: On magnetic resonance (MR) images, strands correspond to curvilinear areas running in the perinephric fat, and haloes to those lying on the renal surface. Our aim was to examine the diagnostic significance and histopathological basis of these areas. PATIENTS AND METHODS: MR images obtained in 46 patients without renal disease and 96 patients with renal disease were assessed for the signal intensity and extent of strands and haloes, and their degree of right-left asymmetry. RESULTS: Strands usually revealed low signal intensity on T1-weighted MR images and high signal intensity on fat-suppressed T2-weighted images and contrast-enhanced fat-suppressed T1-weighted images. Haloes revealed high signal intensity on fat-suppressed T2-weighted images, but most of haloes were not clearly depicted on T1-weighted images or contrast-enhanced fat-suppressed T1-weighted images. Strands and haloes were common and usually symmetrical or only mildly asymmetrical in both patient groups. However, in 11 of the 96 patients with renal disease, prominent strands and/or haloes appeared with remarkable asymmetry and likely represented definite changes in the perinephric fat. At histopathology, vascular loose fibrous tissue was found at the sites of strands and haloes. CONCLUSION: Strands and haloes usually represent normal anatomical variations. However, the presence of prominent strands or haloes with remarkable right-left asymmetry implies abnormality and may provide additional information in the evaluation of renal disease.     

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.     

Magnetic resonance in neoplasms of the adipose, fibrous and muscular tissues

Two-hundred and three MR examinations were reviewed of 177 patients with lipomatous, fibrous and muscular tissues tumors which were evaluated at staging or during the follow-up. All examinations were obtained with a 1.5T superconductive magnet, and both T1 and T2-weighted images were acquired. Its high-contrast resolution, its direct multiplanarity and its allowing both T1 and T2-weighted images to be obtained, are the most important characteristics of MR imaging. In our experience, MRI demonstrated a high overall accuracy (96.1%)-95.2% at restaging alone--with similar sensitivity both at the staging of the disease (100%) and during the follow-up (97%). Overall sensibility was 97.6%. MR specificity in histologically proven relapses was 87.9%. Even though it is gradually assessing itself as the most important method in the evaluation of soft tissues masses, MRI allows an histological diagnosis to be made only in lipomatous tumors and in benign fibrous tumors, due to their specific signal features. The commonest though aspecific finding is a soft tissue mass with relatively low signal intensity in T1 and high signal intensity in T2-weighted images. In our opinion, MR imaging is the method of choice during the follow-up of the disease, whereas it is probably a complementary technique in the staging.     

Solitary fibrous tumor of the pleura: MR appearance and enhancement pattern

PURPOSE: The aim of the current study was to characterize the MR appearance of solitary fibrous tumor of the pleura (SFTP). METHOD: Twenty-two consecutive patients with histologically confirmed SFTP were retrospectively evaluated with MRI. RESULTS: Tumors demonstrated low signal intensity (n = 18, 82%), iso signal intensity (n = 2, 9%), and high signal intensity (n = 2, 9%) on T1-weighted images. On T2-weighted images, tumors were observed as low signal intensity (n = 10, 45%), high signal intensity (n = 2, 9%), and mixed signal intensity (n = 10, 45%). Solid component in the proliferation of tumor cells corresponded to low signal intensity in 12 tumors (55%) on T2-weighted images. On gadolinium-enhanced T1-weighted images, inhomogeneous enhancement (n = 18, 82%), nodular enhancement (n = 6, 27%), and homogeneous enhancement (n = 4, 18%) were observed. The enhanced lesion within the tumors had dense tumor tissue and dilated microvessels in the pathologic specimen. CONCLUSION: SFTP shows variable appearance and enhancement pattern on MRI according to morphologic tumor heterogeneity.     

MRI of malignant fibrous histiocytoma of soft tissue: analysis of 13 cases with pathologic correlation

We reviewed the magnetic resonance (MR) appearances of 13 malignant fibrous histiocytomas (MFH) of soft tissue and correlated each with the respective lesion's histopathology. The MR images were evaluated for signal intensity on T1- and T2-weighted spin echo sequences, homogeneity of the lesion, presence of internal low signal septations, and margin definition. Histologic subtypes of MFH included storiform-pleomorphic, giant cell, myxoid, and inflammatory. We could not establish a correlation between MR appearance and histopathology. Instead, our series exhibited general features suggestive of malignant soft tissue neoplasms, namely poor margin definition, internal low signal septation, and heterogeneous high signal intensity on T2-weighted images.