British Journal of Radiology (2006) 79, 76-78
© 2006 British Institute of Radiology
doi: 10.1259/bjr/97645635
Solitary pulmonary nodule with growth and contrast enhancement at CT: inflammatory pseudotumour as an unusual benign cause
S Diederich, Prof. Dr. med.
1
D Theegarten, Priv. Doz. Dr. med.
2
G Stamatis, Prof. Dr. med.
3 and
R Lüthen, Priv. Doz. Dr. med.
4
1 Department of Diagnostic and Interventional Radiology, Marien Hospital, Academic Teaching Hospital, Rochusstr. 2, D-40479 Düsseldorf, 2 Institute of Pathology, BG-Kliniken Bergmannsheil, Ruhr University Bochum, 3 Department of Thoracic Surgery and Endoscopy, Ruhrland Hospital Essen and 4 Department of Medicine, Marien Hospital Düsseldorf, Germany
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Abstract
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Small (
10 mm) pulmonary nodules are frequently detected at modern chest CT. As most of these nodules are benign, non-invasive classification is required – usually based on assessment of growth and perfusion. Absence of growth and no evidence of perfusion, as demonstrated by lack of enhancement at contrast-enhanced CT or MRI, strongly suggest a benign nodule. On the other hand, growth with a doubling of the nodule's volume between 20 days and 400 days or enhancement suggest a malignant nature of the lesion. We present an example of a nodule with strong contrast enhancement and a doubling time of approximately 260 days, which histologically represented a benign inflammatory pseudotumour.
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Case report
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A 56-year-old asymptomatic male underwent chest radiography in two views as part of a general health survey. This revealed a small non-calcified nodule projected over his right mid lung field not demonstrated on a chest radiograph obtained 3 years previously. CT of the chest (collimation 5 mm) confirmed a non-calcified nodule in the lateral segment of the right middle lobe adjacent to a subsegmental artery and bronchus with a diameter of approximately 9 mm. No other abnormality was demonstrated, in particular no hilar or mediastinal lymphadenopathy was observed.
The patient presented to our hospital for a second opinion 3 months later. Evaluation of size and contrast-enhancement was performed obtaining limited spiral CT data sets with a collimation of 1 mm (Somatom Plus 4; Siemens, Erlangen, Germany) before and 1 min, 2 min, 3 min and 4 min after administration of 1.4 cm3 kg–1 body weight iomeprerol (Imeron 300®; Altana Pharma, Konstanz, Germany) with an injection rate of 2 cm3 s–1. Images were displayed at lung and mediastinal windows (Figure 1a, b, c
). Nodule density was measured in regions of interest representing 70% of the nodule's cross section at anatomically identical levels. Density was 27 Hounsfield Units (HU) before contrast injection and increased to 80 HU, 95 HU, 63 HU and 62 HU after 1 min, 2 min, 3 min, and 4 min. Thus, maximum enhancement after 2 min was 68 HU. The diameter of the nodule was again measured to be 9 mm (Figure 1a).
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Figure 1. Dynamic thin-section CT scan before ((a) lung window, (b) mediastinal window) and 2 min after ((c) mediastinal window) contrast enhancement: The nodule shows an enhancement of 68 Hounsfield units.
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It has been shown that lack of contrast-enhancement almost excludes malignancy with a negative predictive value of 96%, whereas demonstration of contrast-enhancement allows no differentiation between benign and malignant nodules [1]. Thus, the patient was informed that malignancy could not be excluded and biopsy was recommended. Due to the central location of the relatively small nodule adjacent to a subsegmental artery, it was felt that percutanous biopsy was not appropriate and surgical biopsy was suggested. The patient, however, did not agree to immediate biopsy. Therefore, follow-up thin section CT with 1 mm slice thickness was performed at 6 months and 10 months. There was questionable growth at 6 months and definite growth at 10 months (Figure 2). The nodule's volume was calculated from measurements digitally on the monitor of a workstation in the axial plane and also by counting the number of contiguous 1 mm slices for estimation of the diameter in craniocaudad direction. As the nodule appeared almost ideally spherical at the baseline measurement (9 mm) and at 10 month follow-up (12 mm) its volume was calculated (V=4/3 
r3) as 381 mm3 (baseline measurement) and 904 mm3 (10 months) resulting in a doubling time of 8.6 months.
Again surgical biopsy was recommended and now the patient agreed.
As the nature of the nodule could not be established prior to surgery it was decided to proceed to minimally invasive thoracotomy. During surgery a tumour measuring 18 mm x 24 mm adjacent to the medial segmental bronchus of the middle lobe was palpated rendering wedge resection impossible. Due to the small volume of the middle lobe, primary middle lobectomy was performed including resection of regional lymph nodes. Final histological assessment of the well-circumscribed lesion (Figure 3) including immunostaining for CD-1a, CD-3, CD-20, CD-68, and EMA showed a mixed inflammatory infiltrate and connective tissue typically for a benign inflammatory pseudotumour (Figure 4a). Diagnosis of a malignant tumour could not be confirmed. Several vessels were demonstrated within the nodule (Figure 4b). The post-operative course was unremarkable and the patient was discharged from hospital after 8 days.
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Figure 3. Histological slide showing the nodule with focal sclerosis (Haematoxylin and eosin, magnification x 2).
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Figure 4. Histological slides demonstrating a mixed inflammatory infiltrate with lymphocytes and plasma cells ((a) Haematoxylin and eosin, magnification x 200) and involvement of medium-sized vessels with occlusion ((b) CD34 staining, ABC method, magnification x 100).
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Discussion
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Pulmonary nodules are common findings at chest radiography and even more at chest CT. With the introduction of spiral CT, and particularly multirow-detector spiral CT, an increasing number of small nodules (10 mm) is detected. The ratio of benign and malignant nodules strongly depends on nodule size. In nodules >10 mm the proportion of malignant nodules is high requiring biopsy in many cases [2]. In nodules 10 mm more than 90% of nodules are benign [3]. Therefore, biopsy is not routinely performed in these lesions and non-invasive diagnostic tests are required to differentiate between benign and malignant nodules.
The two techniques used routinely are analysis of nodule growth and perfusion. It has been shown that most malignant tumours exhibit doubling times between 20 days and 400 days, whereas faster or slower doubling times suggest benign lesions [4, 5].
Also, assessment of tumour perfusion is helpful in predicting a nodule's nature. As malignant tumours >1 mm require neoangiogenesis for further growth, all malignant tumours visible at chest CT should exhibit enhancement at contrast-enhanced CT or MRI [1].
It has been shown that absence of contrast enhancement strongly predicts the benign nature of a nodule (e.g. granuloma); on the other hand, not all enhancing nodules are malignant due to enhancing benign lesions such as inflammatory nodules or intrapulmonary lymph nodes [1, 6, 7].
Our case is another example of a benign nodule with strong enhancement that also exhibited growth with a volume doubling time suspicious for malignancy.
Inflammatory pseudotumour (other diagnostic terms: fibroxanthoma, xanthogranuloma, xanthofibroma, histiocytoma) is a rare entity histologically composed of a mixture of inflammatory cells, including plasma cells, lymphocytes, macrophages, a few eosinophils, fibroblasts and connective tissue. In cases with dominance of plasma cells, the term plasma cell granuloma is used. The lesions are typically solitary, round and well circumscribed. The diameter varies from 0.8 cm to 36 cm. Pulmonary inflammatory pseudotumours clinically present in 60% of patients with symptoms such as cough, dyspnoea and haemoptysis; 40% are asymptomatic. The lesion presents in patients ranging from 1 year to 77 years, but approximately 60% are under the age of 40 years [8, 9].
Radiologically, most inflammatory pseudotumours present as well-defined nodules or masses measuring between 1 cm and 10 cm. The large difference in the maximum size reported in the literature probably depends on the mode of detection as well as the presence or absence of symptoms. Inflammatory pseudotumours are slightly more common in the lower lobes. If followed radiographically, growth has been documented. Contrast studies usually demonstrate significant enhancement of the lesions. Cavitation or calcification is rare. Infiltration of adjacent organs may be observed and misinterpreted as evidence of malignancy [9, 10]. In symptomatic patients surgical resection is the therapy of choice.
In conclusion, inflammatory pseudotumour has to be included in the differential diagnosis of enhancing pulmonary nodules with growth particularly in children and young adults. As there is no specific imaging feature, biopsy is required for the diagnosis.
Received for publication February 24, 2005.
Revision received April 18, 2005.
Accepted for publication April 29, 2005.
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References
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Abstract
Case report
