FDG PET is well recognized for its utility in cancer workup. Nonetheless, the differentiation between malignant and benign pulmonary lesions by FDG PET is challenging. The authors report three proved cases of pulmonary tuberculosis in acute active and open stages. The activities and extents of infection were demonstrable in FDG PET, which could not be observed in either chest radiograph or computed tomography.

Cryptococcosis is not uncommon. Potential interpretation pitfalls should be kept in mind when fluorodeoxyglucose (FDG) positron emission tomography (PET) is used for differentiating pulmonary nodules and for discriminating infection from malignancy, especially in areas where the prevalence of granulomatous infection is high and in immunocompromised patients. In this case, a nodular mass was shown on chest radiography and computed tomographic (CT) scanning. A consolidated infection or a bronchioloalveolar carcinoma was suspected because the CT scan showed air bronchograms within the mass and another perihilar infiltration. The FDG PET scan clearly delineated the lesion and had intermediately high glucose uptake (standard uptake value, 3.8-4.0), which led to the exclusion of the possibility of bronchioloalveolar carcinoma because most of these tumors had normal or mildly increased FDG accumulation. Cryptococcoma was finally diagnosed. Hence, the CT scan and FDG PET played complementary roles in the differential diagnosis of this nodular mass.

We report a patient with a solitary spinal neurofibroma in the posterior mediastinum interpreted as a metastatic tumor. A 46-year-old female with rectal cancer who had undergone operation and subsequent adjuvant chemotherapy two years previously was referred to our department for a follow-up whole body FDG-PET study. PET scan revealed a mass with increased uptake of FDG (SUV = 4.6) in the posterior mediastinum. MRI examination showed a dumbbell neurogenic tumor originating from the intercostal nerve at T6 level. A subsequent CT-guided biopsy demonstrated a neurofibroma.

Chronic pancreatitis is a relatively common disease. We enco un tered tw o d if f erent c a s es o f bel atedly demonstrated pancreatic carcinoma featuring underlying chronic pancreatitis. The first case was one that was highly suspected as that of a malignancy based upon imaging study, but unfortunately, it could not be confirmed by intra-operative cytology at that time. Following this, the surgeon elected to perform only conservative bypass surgery for obstructive biliary complication. Peritoneal carcinomatosis was later noted and the patient finally died. The second case, a malignant mucinous neoplasm, was falsely diagnosed as a pseudocyst, based upon the lesion's sonographic appearance and associated elevated serum amylase levels. After suffering repeated hemoptysis, the patient was found to exhibit lung metastasis and peritoneal seeding. We reviewed some of the literature, including those studies discussing chronic pancreatitis predisposing to a malignant change. These two case analyses illustrate clearly that the diagnosis for such conditions, which is simply based upon imagery or pathological considerations may end up being one of a mistaken malignancy. Some of our suggestions for the treatment of such malignancies as revealed herein include, total pancreatomy for univocal mass lesion, and needle aspiration of lesion-contained tissue for amylase, CA199 and CEA levels for a suspicious cystic pancreatic mass.