Hepatic perivascular lymphedema: CT appearance

The CT appearance of dilated hepatic lymphatics in liver transplant recipients has been described recently. We have observed similar findings of presumed hepatic lymphatic dilatation and perivascular lymphedema in 20 patients seen over an 8-month period, none of whom had received a liver transplant. Review of these patients' records showed that 18 (90%) of 20 had underlying disease processes that could have caused dilated lymphatics as a result of either increased lymph flow or lymphatic obstruction. We have grouped these processes into three etiologic categories: (1) posttraumatic hepatic lymphatic obstruction, (2) obstruction caused by malignant lymphadenopathy, and (3) congestive hepatomegaly caused by cardiac decompensation. The appearance of hepatic lymphatic dilatation and surrounding lymphedema needs to be recognized so that lymphatic dilatation is not mistaken for dilated intrahepatic bile ducts.     

Hepatic cirrhosis: magnetic resonance imaging

The effect of periportal collagen deposition on magnetic resonance images and T1 and T2 relaxation times was studied in the rat. Hepatic cirrhosis was induced in 29 rats by chronic intraperitoneal thioacetamide injections. Another 14 rats in which liver abnormalities did not develop were used as controls. The rats were imaged using a small-bore resistive magnet. Histologic correlations and hydroxyproline measurements were performed to document the changes in periportal collagen deposition. The T1 and T2 relaxation times, determined both in vivo and in vitro with spectroscopy, were compared between the normal group and the group with moderate to severe histologic evidence of cirrhosis. The deposition of two to four times the normal amount of collagen in the liver did not affect the T1 or T2 relaxation time. Relatively pure periportal collagen fibrosis does not appear to affect the magnetic resonance image or T1 or T2 relaxation times of the rat liver.     

Lemierre syndrome: magnetic resonance imaging and computed tomographic appearance

Lemierre syndrome consists of septic thrombophlebitis of the internal jugular vein secondary to oropharyngeal infection, usually with Fusobacterium necrophorum. Septic metastatic emboli and distant infection are characteristic. We describe the imaging appearance of Lemierre syndrome in an adolescent female by both magnetic resonance imaging and computed tomography. This case illustrates the rapid onset and characteristic progression of the rare syndrome of Lemierre. In addition, we used magnetic resonance imaging to effectively distinguish between inflammatory venous thrombosis and abscess, thus avoiding surgery in our patient. Early directed antibiotic therapy is mandatory to ensure good outcome.     

The magnetic resonance imaging appearance at 1.5 Tesla of cartilaginous tumors involving the epiphysis

Three cases of lytic, calcified epiphyseal lesions with plain film and computed tomography features suggestive of chondroblastoma were imaged by magnetic resonance imaging. Histopathologic correlation was obtained in each case. Two cases of chondroblastoma showed low signal intensity on both short (TR600/TE20ms) and long (TR2500/TE80ms) spin echo (SE) images. The third case, a clear cell chondrosarcoma, demonstrated increased signal intensity on moderately T2 weighted (TR2500/TE40ms) images. These findings suggest that magnetic resonance imaging may be helpful in distinguishing these lesions.     

Subacute osteoporotic compression fracture: Misleading magnetic resonance appearance

Three patients with benign subacute ostcoporotic vertebral compression fractures are presented. T₁ weighted magnetic resonance (MR) images (SE 500/30) showed decreased vertebral signal. Because the results of the MR examination were thought to indicate malignant disease, extensive medical workups, including one biopsy, were pursued in all three patients. Routine (SE 500/30) spin-echo pulse sequences cannot definitively distinguish between benign and malignant vertebral compression fractures.     

Orbital imaging: factors determining magnetic resonance imaging appearance

This article addresses the dependence of the image characteristics in MR imaging of the orbit. Among the variables discussed are signal-to-noise (SNR), field of view (FOV), spatial resolution, and their interdependence. It is further shown how image contrast can be controlled by judicious choice of pulse timing parameters and how contrast depends on the intrinsic tissue MR parameters T1, T2, and proton density.     

Hepatic tumors: differentiation by transverse relaxation time (T2) of magnetic resonance imaging

Fifty-three patients who had hepatic tumors (24 hepatomas, ten metastases, and 19 cavernous hemangiomas) underwent MR imaging using a 0.35-T superconducting imager. The transverse relaxation time (T2) was calculated from a pair of spin echo images (repetition time [TR] of 1600 msec) with echo delay times (TE) of 35 and 70 msec. The computed T2 value was obtained in a fashion similar to that used to obtain CT numbers with region-of-interest cursors. The mean T2 was 59 +/- 9 msec in hepatomas, 64 +/- 15 msec in metastases, and 100 +/- 30 msec in hemangiomas. The difference between the T2 of hemangioma and that of liver malignancies was statistically significant (P less than .001); however, differentiation between hepatoma and metastases was not possible. The T2 was shorter than 80 msec in all 24 hepatomas and in nine of ten metastases, and was longer than 80 msec in 16 of 19 hemangiomas. Forty-nine of 53 cases (92%) were correctly classified when the borderline of T2 between hemangioma and hepatic malignancies was set at 80 msec. MR with T2 calculation was valuable in differentiating between hemangioma and hepatic malignancies.     

Radio-frequency-induced thermal lesions: subacute magnetic resonance appearance and histological correlation

PURPOSE: To investigate the relationship between subacute magnetic resonance (MR) images of radio-frequency (RF) ablation lesions and tissue viability as determined from histological tissue samples. MATERIALS AND METHODS: We generated lesions (N = 5) in a rabbit thigh model. Four days later, we obtained in vivo T(2)- and contrast-enhanced (CE) T(1)-weighted images and ex vivo histological samples approximately perpendicular to the electrode path. Using three-dimensional registration and warping, we spatially compared manually segmented boundaries apparent on MR images to boundaries separating distinct histological zones determined from hematoxylin and eosin (H&E) and Masson trichrome (MT) stains, as well as birefringence studies. RESULTS: Lesions have a characteristic MR appearance: an outer hyperintense margin (M2) separating background tissue (M3) from an inner core (M1), in both T(2) and CE T(1) images. Histologically, there are two zones of damage: an outer zone of likely nonviable cells (H2) separating background tissue (H3) from an inner core of coagulated nonviable cells (H1). We measured distances between automatically computed correspondence points along histological and MR boundaries. For T(2) and CE T(1) images, respectively, M1 vs. H1 distances were 0.72 +/- 0.99 mm (mean +/- SD) and 0.10 +/- 0.95 mm, while outer M2 vs. H2 boundary distances were 0.26 +/- 1.16 mm and 0.05 +/- 1.08 mm. The discrepancy between histological and MR boundaries was larger than the variability in segmenting MR images, but probably within registration error. There were no significant differences between T(2) and CE T(1) boundaries. CONCLUSION: Lesion boundaries apparent in both T(2)- and CE T(1)-weighted MR scans, performed several days postablation, similarly predict the histological response. That is, the lesion core (M1) corresponds to nonviable coagulated cells (H1), while the hyperintense margin (M2) corresponds to likely nonviable cells undergoing necrotic changes (H2).     

Fibrous dysplasia: magnetic resonance imaging appearance at 1.5 tesla

Fibrous dysplasia has been described in a small number of cases in the literature as showing low signal intensity on T1- and T2-weighted magnetic resonance images. We reviewed magnetic resonance scans of 13 patients with fibrous dysplasia to determine if there might be a characteristic appearance. All lesions had sharply defined borders and were of intermediate signal intensity on T1-weighted images. With T2 weighting, six lesions (46%) showed high signal intensity, four (31%) showed persistent intermediate signal intensity, and three (23%) showed mixed intermediate and high signal intensity. Ten lesions (77%) had inhomogeneous signal intensity and three (23%) had homogeneous signal intensity. We concluded that fibrous dysplasia does not have a characteristic appearance on magnetic resonance imaging. However, magnetic resonance may be helpful in establishing the diagnosis of fibrous dysplasia if low to intermediate signal intensity is seen on both T1- and T2-weighted images. This situation occurred in 54% of our cases, whereas the other 46% had nonspecific signal characteristics indistinguishable from many other bone lesions.     

Neonatal tuberous sclerosis: magnetic resonance appearance of subependymal tubers

A case of tuberous sclerosis in a neonate, with cerebral and cardiac hamartomas evaluated by MR imaging, is presented. Intracranial subependymal tubers in this neonate exhibit increased signal intensity on short TR images. This differs from the signal characteristics of subependymal tubers in older patients.     

Magnetic resonance appearance of peripheral nerve sheath tumors

Magnetic resonance imaging (MRI) was used to evaluate 22 histologically proven peripheral nerve sheath tumors, approximately two-thirds of which arose in the lower extremity. The histologic distribution was as follows: 12 schwannomas, 7 neurofibromas, and 3 malignant peripheral nerve sheath tumors (2 of which occurred in patients with neurofibromatosis). Most lesions demonstrated an intermediate to moderately bright signal on T₁-weighted images and were minimally inhomogeneous. All lesions were moderately bright on proton-density-weighted images and bright on T₂-weighted images, again with variable inhomogeneity. The extent of the tumor was best assessed on proton-density- and T₂-weighted images. Smooth margins were noted in 19 lesions. Of the 3 remaining lesions, 2 were malignant (but had been subjected to biopsy prior to MRI), and the other lesion was a plexiform neurofibroma. MRI accurately determined the relationship between the lesion and the adjacent neurovascular structures and muscles, thereby assisting surgical management. On MRI, 5 lesions demonstrated coexistent subtle muscle atrophy along the longitudinal axis of surrounding or distally innervated musculature. This latter finding, together with the presence of a tumor in the vicinity of a large nerve trunk, suggests a peripheral nerve sheath neoplasm.The opinions and assertions contained herein are the private views of the authors and do not reflect the views of the Uniformed Services University of the Health Sciences, the Department of the Army, or of the Department of Defense     

CT appearance of some colonic villous tumors.

OBJECTIVE: A review was made of the CT studies and pathology reports of four patients with surgically resected colonic villous adenomatous tumors, two of whom had focal carcinomatous invasion. CONCLUSION: Two patients had villous tumors with IV contrast-enhancing convolutional gyral patterns. The other two patients had tumor masses that showed oral contrast medium collecting in surface interstices, analogous to findings with barium enemas. One of the latter also had an unusual cluster of mesenteric vessels adjacent to the lesion.     

Hepatic vascular anatomy on magnetic resonance imaging

This study evaluated the ability of magnetic resonance imaging (MRI) to depict the hepatic vasculature and surgical anatomy of the liver using the transaxial, coronal, and sagittal planes. Retrospective analysis of the abdominal MRI examinations of 94 patients was performed. The spin-echo imaging technique was used to obtain transaxial images in all patients and coronal and sagittal sections in 35 of these patients. Overall, the hepatic vasculature was better delineated on the longer repetition rates (2000 msec TR) and the first echo images (28 msec TE). The inferior vena cava, right and middle hepatic veins, and main and right portal veins were seen in 100% of the cases in the transaxial plane. The left hepatic vein was seen in 98%, the left portal vein in 93%, and the hepatic artery in 44% in the transaxial plane. In the sagittal and coronal planes, the inferior vena cava and main and right portal veins were seen in 100% of cases. The other hepatic vasculature was less frequently demonstrated. In the sagittal plane, the right hepatic vein was seen in 85% of the cases, the left hepatic vein in 62%, the middle hepatic vein in 90%, the left portal vein in 90%, and the hepatic artery in 14%. In the coronal plane, the right hepatic vein was seen in 85% of cases, the left hepatic vein in 14%, the middle hepatic vein in 79%, the left portal vein in 71%, and the hepatic artery in 7%. These results are from preliminary work. Further developments with MRI technology may render better visualization of hepatic vasculature.     

Occult intraosseous fracture: magnetic resonance appearance versus age of injury

Twenty-two cases of occult intraosseous fracture in the region of the knee are presented. Occult intraosseous fractures have been incidentally detected in the magnetic resonance (MR) evaluation of the knee in the setting of a recent physical injury and normal radiographic studies. There is no unique mechanism of injury, but occult intraosseous fracture presumably results from direct impaction or axial overloading. MR shows speckled or band-like areas of low signal in the intramedullary space of the epiphyses, and occasionally, the adjacent metaphyses. In most cases, T2-weighted images show high signal in corresponding regions of variable size. The relative extent of high signal findings is shown to vary significantly with the age of injury. Individual variability within groups, however, precludes the actual prediction of lesion age on the basis of the MR appearance. Our observations provide indirect evidence that the findings on T2-weighted images resolve earlier than the corresponding findings on T1-weighted proton density images. The primary differential diagnosis in cases of occult intraosseous fracture is stress fracture. The diagnosis of occult intraosseous fracture may be important in explaining persistent pain after injury in otherwise normal knees.     

Calcific tendinosis and periarthritis: classic magnetic resonance imaging appearance and associated findings

Calcification within tendon and periarticular soft tissues with or without a history of pain is commonly encountered in the interpretation of musculoskeletal MR imaging (MRI) studies. This article presents a pictorial illustration of both the classic and atypical MR imaging (MRI) features of soft tissue calcifications in the musculoskeletal system. Familiarity with this topic can help to avoid pitfalls in imaging diagnosis.     

Bone tumors: magnetic resonance imaging versus computed tomography

The magnetic resonance (MR) imaging characteristics of bone tumors are described and the clinical utility of MR imaging in patient evaluation is reported. Fifty-two patients with skeletal lesions were examined with a Picker MR imager (0.15-T resistive magnet). Twenty-five patients had primary malignancies, seven had benign bone neoplasms, 15 had skeletal metastases, and five had neoplasm simulators. Forty-five patients had CT scans available for comparison. For demonstrating the extent of tumor in marrow, MR was superior to CT in 33% of cases, about equal to CT in 64%, and inferior to CT in 2%. For delineating the extent of tumor in soft tissue, MR was superior to CT in 38% of cases and about equal to CT in 62%. CT was superior in all cases for demonstrating calcific deposits and pathologic fractures. In four patients with metal prostheses or surgical clips, MR was superior to CT in documenting recurrent tumor because of artifactual degradation of the CT image. Direct sagittal and coronal images from MR permit accurate assessment of the relationship of tumor to adjacent normal structures, including the physis, joints, and neurovascular structures. MR is useful in the evaluation of bone tumors: it is of greatest value in evaluations of the peripheral skeleton, the medullary canal, soft tissues, and postoperative tumor recurrence. With a 0.15-T magnet, MR is less useful in the evaluation of the axial skeleton and cortical bone.     

肝脏肿瘤射频消融术后螺旋CT表现及临床意义

目的：研究肝肿瘤经皮射频消融治疗后的典型和不典型CT表现并分析其临床意义。方法：52冽原发和肝转移瘤患者经皮射频消融术后或术后1月,如果效果显著3月后应用CT三期增强扫描。结果：根据肿瘤灶毁损的程度及时间的变化,消融区影像表现差异大。结论：肝脏肿瘤消融术后螺旋CT扫描,尤其是三期增强扫描对治疗后的疗效及并发症可作出精确的影像诊断,对确定肿瘤残存及复发与否有着重要的作用。     

Reactive sclerosis: hyperintense appearance on T2-weighted magnetic resonance imaging

Osteosclerosis is defined as increased density of bone on X-ray imaging studies. It is known that osteosclerosis appears hypointense on both T1- and T2-weighted magnetic resonance imaging sequences. In this review, we present our experience in various sclerotic skeletal pathologies that appear hyperintense on T2-weighted magnetic resonance imaging. We emphasize the possible pathophysiological mechanisms that may cause this appearance, such as bone marrow edema and/or composition of newly formed bone.     

Hepatic cavernous hemangioma: magnetic resonance imaging. Work in progress

Using a 0.35-T superconducting magnet and spin echo imaging, we prospectively evaluated 11 patients who had proved hepatic cavernous hemangioma. Magnetic resonance (MR) identified more lesions than either contrast-enhanced CT, or ultrasonography. The MR appearance was consistent; hemangiomas were homogeneous and generally isointense at short TR and TE intervals but were hyperintense at long TR intervals and greatly hyperintense at long TR and long TE intervals. However, the MR appearance of hemangioma was not specific; 2/14 other focal hepatic masses had similar features. The calculated relaxation times (T1, T2) were not useful in lesion characterization, although the intensity ratio of hemangioma to normal liver at the TR = 2.0 sec TE = 56 msec pulse sequence was useful in diagnosis since hemangiomas always had a ratio greater than 1.4.