Radiological Diagnosis

Inflammatory Pseudotumor of Lung

The chest radiograph reveals a sharply circumscribed solitary pulmonary mass lesion in the left lower lobe with amorphous dense calcification within it. CT of the chest reveals a large, lobulated heterogeneous mass with foci of dense calcification without any cystic areas. The surrounding lung parenchyma is normal. CT guided fine needle aspiration cytology and biopsy were inconclusive. A presumptive diagnosis of hamartoma or inflammatory pseudotumor of the lung (plasma cell granuloma) was preoperatively entertained. At surgery a 10x 7 x 6 cm mass was present in the postero medial aspect of the left lower lobe which was removed with part of the adjacent lung parenchyma.

Microscopic examination showed the lesion to be composed of a mixture of spindle cells, fibroblasts, myofibroblasts and inflammatory cells principally plasma cells and a focal collection of lymphocytes with areas of calcification and hyalinization. Based on these findings a diagnosis of inflammatory pseudotumor was made.

Inflammatory pseudotumor of the lung is an uncommon benign non-neoplastic mass lesion that usually originates as an organizing intraalveolar pneumonia [1]. Based on the histologic findings, the lesions can be subdivided into (a) organizing pneumonia (b) fibrous histiocytoma (c) lymphoplasmacytic types.

Inflammatory pseudotumor is the most common primary lung mass seen in children [2]. Approximately 33-40% of patients at the time of diagnosis are less than 20 years of age and the peak incidence is in the second decade of life [3],[4]. There is no sex predilection and most patients are asymptomatic though recent reports suggest that the majority of patient have one or the other symptom, which includes non productive cough, dyspnea, lower respiratory tract infection, hemoptysis, fever and chest pain [4]. The origin of inflammatory pseudotumor remains unclear though autoimmune and the origins of the infections have been hypothesized [5].

Chest radiographs usually reveal a solitary, well-circumscribed round or oval mass, with or without a lobulated border with an anatomic bias for lower lobes. Radiologically visible calcification is seen in upto 15% of patients [4]. However microscopic evidence of calcification within the tumor can be more commonly appreciated [3]. Calcification is more common in children and adolescent patients when compared to adults and can be punctate, curvilinear, dense or flocculent in nature [6].

CT scan findings are variable and nonspecific and most commonly demonstrate a well-marginated lobulated mass of heterogeneous attenuation with variable patterns of contrast-enhancement and calcification [4]. MR findings of inflammatory pseudotumor have been confined to only a few case reports [4] [7] and show heterogeneous / homogeneous signal intensity iso/hyperintense to that of skeletal muscle in T1W images and slightly hyperintense on T2W images.

The radiologic differential diagnosis for inflammatory pseudotumor includes both primary and metastatic neoplasms. In children without any underlying malignancy, a solitary pulmonary nodule or mass is more likely to be an inflammatory pseudotumor rather than a neoplastic process. Benign tumors that may mimic these lesions include hamartoma, chondroma and sclerosing hemangioma of pulmonary parenchyma. The malignant tumors that should be ruled out include pseudosarcomatous spindle cell carcinoma and pulmonary sarcoma [8]. Early and complete surgical resection is essential to effect cure and to exclude malignancy in aggressive cases and is the treatment of choice.