British Journal of Radiology (2007) 80, e141-e144
© 2007 British Institute of Radiology
doi: 10.1259/bjr/98272327
Fibrosing mediastinitis manifesting as thoracic prevertebral thin band-like mass on MRI and PET-CT
K Y Lee, MD1,
J G Yi, MD2,
J H Park, MD2,
Y J Kim, MD2,
Y So, MD3 and
J S Kim, MD4
1 Department of Internal Medicine, 2 Department of Radiology, 3 Department of Nuclear Medicine, 4 Department of Thoracic Surgery, Konkuk University College of Medicine, Seoul, Republic of Korea
Correspondence: Dr Jeong Geun Yi, Diagnostic Imaging, Konkuk University Hospital, 4-12 Hwayang Gwangjin, Seoul 143729, Republic of Korea. E-mail: yinatur{at}kuh.ac.kr
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Abstract
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To our knowledge, no report exists of a posterior mediastinal thin band-like mass as a manifestation of fibrosing mediastinitis. A man showed right pleural effusion on chest radiograph. On CT, there was a band-like mass on thoracic prevertebral area. MRI demonstrated the enhancing longitudinal band-like mass all along the vertebrae on coronal and sagittal scans. It was hypermetabolic on PET–CT and there was another hot mass in the presacral area. Additional pelvic MRI showed presacral mass with aortic encasement. Biopsy specimen was consistent with fibrosing mediastinitis. We report a case of fibrosing mediastinitis of posterior mediastinum manifesting as thoracic prevertebral band-like mass and discontiguous presacral, periaortic mass studied with CT, MRI and PET-CT.
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Introduction
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Fibrosing mediastinitis is a rare condition of uncertain cause, characterized by replacement of normal mediastinal tissue with acellular collagen, fibrous tissue and/or chronic inflammatory tissue [1, 2]. This disease is also known as sclerosing mediastinitis and mediastinal fibrosis. Fibrosing mediastinitis typically presents as middle mediastinal or hilar mass. Most patients present with signs and symptoms of obstruction of the superior vena cava, pulmonary veins or arteries, large airways and oesophagus. Although most of the cases are idiopathic, many are thought to be caused by an abnormal immune reaction to Histoplasma capsulatum or Mycobacterium tuberculosis and sometimes by malignancy [2–5].
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Case report
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A 74-year-old man was referred to our hospital with complaints of fever and chill over the previous 4 weeks. Chest radiographs showed a small amount of pleural effusion on the right side. The heart was not enlarged and lung parenchyma looked normal. A computed tomography (CT) (LightSpeed Pro 16; General Electric Medical Systems, Milwaukee, WI) was performed to find the etiology of pleural effusion. On axial chest CT, a diffuse homogeneous soft tissue band-like mass was shown all along the thoracic vertebrae which was enhanced after intravenous contrast injection and right pleural effusion was demonstrated (Figure 1
). There was no anterior, middle mediastinal and hilar lesion. Lung parenchyma showed emphysema, without evidence of histoplasmosis or tuberculosis, and thoracic vertebrae showed no tuberculous change. For further evaluation, the patient underwent magnetic resonance (MR) imaging (HD excite 1.5-T system; General Electric Medical Systems, Milwaukee, WI). The band-like longitudinal posterior mediastinal mass was shown on coronal and sagittal MR scans with high signal intensity on T1 weighted images and intermediate signal intensity on T2 weighted images, and was homogeneously enhanced after intravenous contrast administration (Figure 2a,b). Vertebral bodies were normal without evidence of spine tuberculosis on MRI. Fluorodeoxyglucose (FDG) positron emission tomogram (PET)-CT was performed for evaluation of the metabolic status of the lesion and to elucidate the hidden malignancy. Posterior mediastinal mass was hypermetabolic (maximum SUV: 3.5) on PET-CT and there was another longitudinal hypermetabolic lesion in the presacral area with a similar degree of uptake (Figure 3). Pelvic MRI showed the presacral mass extending up to the lower abdomen and encasement of the aorta (Figure 4). PET-CT scan of peri-aortic lesion was hypermetabolic with a similar degree of uptake to that of the prevertebral lesion, which could be misdiagnosed as aortitis (Figure 5). Histopathology from thoracoscopic biopsy showed fibroblasts with inflammatory infiltrates of lymphocytes, histiocytes and plasma cells, consistent with fibrosing mediastinitis or retroperitoneal fibrosis; immunohistochemical stains showed no evidence of lymphoma and carcinoma. The pleural fluid aspirated during biopsy was exudate (total protein: 4.0 g dl–1, LDH, lactic dehydrogenase: 608 IU l–1) with no evidence of tuberculosis. Follow-up CT scans after 2 months of steroid treatment showed marked improvement of the posterior mediastinal mass and pleural effusion (Figure 6).
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Figure 1. Contrast-enhanced axial chest CT shows the band-like soft tissue mass, anterior paravertebral in location with homogeneous enhancement (arrows). Anterior and middle mediastinum are preserved.
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Figure 2. MR images of the thoracic spine.(a) Coronal fast spin-echo T1 weighted image (TR/TE 750/12) shows symmetric band-like soft tissue mass of high signal intensity (arrows). (b) Contrast-enhanced coronal fast spin-echo fat-saturated T1 weighted image (TR/TE 716/12) shows marked and homogeneous enhancement of the band-like paravertebral mass (arrows).
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Figure 3. Sagittal FDG fused PET-CT image of the whole body shows band-like hypermetabolic foci, and thoracic prevertebral and presacral areas.
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Figure 4. Axial fast spin-echo T1 weighted MR image (TR/TE 650/9) of the pelvis shows soft tissue mass encasing the abdominal aorta (arrows).
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Figure 6. Follow-up contrast-enhanced CT after steroid treatment shows an improvement in prevertebral mass (arrows) and a decrease in right pleural effusion.
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Discussion
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Fibrosing mediastinitis is an uncommon benign mediastinal disease characterized by proliferation of dense fibrous tissue in the mediastinum [2–8]. Patients may present with dyspnea, hemoptysis, hoarseness, pleuritic pain, fever, superior vena cava syndrome, weakness, dysphagia or are sometimes asymptomatic, according to the anatomy involved. Despite extensive investigation, the precise etiology and pathogenesis remains elusive. Many, if not most, cases have been linked to Histoplasma capsulatum or Mycobacterium tuberculosis infection [2, 4, 8].
Sherrick et al described two patterns of involvement on CT scans: a focal pattern and a diffuse pattern [4]. The focal pattern (82% of cases) manifests as a mass of soft tissue density, frequently with calcifications (63%), and is usually located in paratracheal, subcarinal regions of the mediastinum or hilar area, more commonly on the right side. Many of these cases are associated with either histoplasmosis or tuberculosis, and resistance to treatment. The diffuse pattern, seen in 18% of cases, manifests as a diffusely infiltrating, often non-calcified mass that affects multiple mediastinal compartments. These patients do not have evidence of granulomatous infection and some are associated with other idiopathic fibrosing disorders such as retroperitoneal fibrosis, sclerosing cholangitis, Riedel's thyroiditis and systemic sclerosis, and are usually responsive to steroid treatment [2, 4]. The findings of our case — location of mass, no calcifications, no evidence of granulomatous inflammation, associated retroperitoneal fibrosis, and improvement after steroid therapy — support that this case could be a diffuse type.
Diagnosis requires clinical suspicion, multiple imaging studies including CT or MRI and finally histological confirmation. In this case, chest radiographs showed pleural effusion only. Mass was not apparent on radiographs because the soft tissue band was thin and even in thickness along the thoracic vertebrae. CT and coronal, sagittal MRI showed a non-calcified, thin rim of tissue, which was continuous on posterior mediastinum and could not be easily differentiated from neurofibromatosis, malignant lymphoma and extramedullary haematopoiesis. CT and multi-planar MRI are the modalities of choice for evaluating the extent of disease. After administration of intravenous contrast media, the mass showed homogeneous enhancement, suggestive of an active inflammatory process. The degree of enhancement of fibrosing mediastinitis or retroperitoneal fibrosisis can be variable depending on the stage of the fibrotic process [2, 9]. In the early stages, the immature tissue is more vascular and enhances to a greater degree, as in our case [2, 9]. At a later stage, avascular mass shows little enhancement.
This posterior mediastinal mass was hypermetabolic on FDG PET-CT, and we found another FDG-avid mass at the presacral area encasing the aorta, which could be life-threatening in the near future (Figure 3
). Presacral mass could have been missed without PET-CT. FDG PET findings of fibrosing mediastinitis have been reported in a single case [7]. In that case, the mass showed no significant uptake initially when the biopsy specimen was non-diagnostic; 18 months later, the mass showed marked uptake on PET with SUV of 5.1. Histopathological diagnosis of sclerosing mediastinitis was confirmed from the area of maximum FDG uptake. Therefore, PET-CT examination must be considered among patients with fibrosing mediastinitis or retroperitoneal fibrosis for selection of the biopsy site and for hidden focus of the disease.
In conclusion, fibrosing mediastinitis presenting as posterior mediastinal mass is rare. Recognition of this atypical pattern of fibrosing mediastinitis, thin fibrous prevertebral band, may be important in differentiating this disease from malignant lymphoma, neurofibromatosis and extramedullary haematopoiesis.
Received for publication January 17, 2006.
Revision received March 15, 2006.
Accepted for publication April 24, 2006.
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Abstract
Introduction
