An intrathoracic schwannoma case in ¹⁸F-FDG PET/CT scan

Positron emission tomography /CT images showed a moderately increased ¹⁸F-FDG uptake in the mass of left lung lower lobe superior segment (SUVmax: 2.71). No pathological ¹⁸F-FDG involvement was detected in another region of the whole body scan. The patient underwent tru-cut biopsy. Since histopathological diagnosis could not be made, thoracotomy was performed. Schwannomas are the second most common benign peripheral nerve sheath originated tumor. Due to its development from Schwann cells, it can be seen in all organs or tissues during intracranial, extracranial, or spinal nerve courses where these cells are found. Schwannomas are extremely rare in the lung, regardless of the patients age. Ohtsuka et al. (2005) stated that in the review of 62 patients with intrapulmonary or bronchial schwannoma (5-83 years; 28 male, 34 female patients), this neoplasm constitutes approximately 0.2% of all pulmonary neoplasms. Although it is usually sporadic and single lesion, it can also be seen with neurofibromatosis (NF)1 or NF2. Especially in schwannomatosis cases, NF2 is observed with multiple and benign characters. In patients with tumors located proximal to the lobar bronchus, atelectasis or pneumonia associated with cough and dyspnea may occur. However, most patients with peripheral intrapulmonary schwannoma have no symptoms. Fluorine-18 FDG-PET/CT is a useful imaging modality to separate malignant solitary pulmonary nodules from benign nodules. There are few cases of ¹⁸F-FDG PET/CT imaging intrapulmonary schwannoma in the literature. Maximum standard uptake values (SUVmax) of Schwannomas in ¹⁸F-FDG PET/CT are variable. SUVmax values are generally low and moderate, but have been shown to vary between 1.9-7.2. The reason for the variation in SUVmax is thought to be due to varying degrees of cellularity, microvascular density or vascular permeability. Histopathologically, dense cellular areas (Antony A) and more hypocellular areas (Antony B) specific to Schwannoma appear in varying proportions. Also, the structure formed by spindle schwann cells side-by-side within the fields of Antony (Verocay body) is characteristic. Surgical resection, endoscopic resection and yttrium aluminum garnet (YAG) laser resection were used for the treatment of primary intrapulmonary schwannoma. The contribution of ¹⁸F-FDG PET/CT in schwannoma is that it provides malign and benign distinctions of intrapulmonary masses. However, a cutoff for SUVmax has not been identified in the malignant benign distinction. The diagnosis must be verified histopathologically.