Teaching Case

Examined twice with CT of the thorax at four months interval .

A 66 year old male, cigarette smoker, presented with hystory of cough, and recent appareance of bloody sputum. Chest radiograms showed an opacity of the right upper lung lobe and bronchoscopy and biopsy revealed a primary squamo-cellular carcinoma. Conventional chest and abdominal CT were performed at our institution for tumour staging. CT scans confirmed the tumoral lesion of the right upper lobe associated with perifocal satellite nodules and thickening of the postero-lateral parietal pleura; no thoracic or abdominal metastases were detected. The patient refused surgery and underwent antiblastic chemotherapy. Conventional chest and abdominal CT were repeated four months later and revealed the enlargement of the neoplastic mass lesion as well as the appareance of a metastatic nodule, 6 mm in diameter, located in the medial segment of the right lower lobe. We evaluated the CT scans obtained four month earlier and we retrospectively detected a micronodule located at the same site.

Lung cancer represents the leading cause of cancer related death in western world; for these reasons there is an urgent need for improvement in diagnosis and management. Chest CT is considered more sensitive than chest radiography for the detection of nodules of lung cancer, but the potential for missing minute cancerous lesions is the major shortcoming of chest CT.Spiral CT improves the detection rates of small lung nodules but the most appropriate diagnostic criteria for minute lung cancers should be still established.Small pulmonary nodules, (less than 1 cm in diameter), represent a relevant diagnostic challenge because the accuracy of available diagnostic procedures is often unsatisfactory owing to their small size (4). Small lung cancer nodules can be missed in prospect but easily seen in retrospect, and we must realize that a cancer lesion can be clearly recognized when the location is known, but go totally undetected in a prospective search (2). QUESTIONS RELATED TO MISS DETECTION: Detection failures are probably due to: the low resolution of the imaging technique, the lesions growth that allows nodules detection at following examinations and the different ability of the observers to detect subtle nodules or in differentiating from other structures as pulmonary vessels (3). An aid to reduce the number of detection failures is given by the use of spiral CT that allows to detect all nodules noted at conventional CT, as well as additional small nodules, but we believe that actually the most important tool to prevent the misdiagnosis of small lung nodules is based onto the careful examination of CT images by expert radiologists (1)(5). Small nodules can be metastases or primary tumours: a second primary lung cancer can also occour synchronously or metachronously and must be differentiate from metastases because of a second primary lung cancer can be surgically treated . UNDERSTAGING Another question is related to the understaging of primary lung cancers. Mediastinal adenopathy are currently evaluated on chest CT but there is a relevant percentage of misdiagnosis that prevents to establish the correct patient's prognosis. Actually PET associated with CT is significantly more accurate than CT alone in the N staging of non small cells lung cancer.