PET/CT imaging of giant primary pulmonary meningioma: a case report and literature review

Meningiomas are common tumors of the nervous system originating from arachnoid cells, which often occur intracranially or in the spinal canal, and are mostly benign. Meningiomas occurring in tissues and organs not covered by meninges are called ectopic meningiomas which are very rare tumors that commonly occur in the head and neck or, less frequently, in the skin [1, 2]. Primary meningioma in lung tissue is defined as primary pulmonary meningioma. Since the first case report in 1982 by Kemnitz et al [3], only a small number of cases of PPMs have been reported. With the development of medical imaging disciplines, we can make a preliminary diagnosis or differential diagnosis of PPM through imaging. Herein, we report a case of a giant PPM diagnosed with ¹⁸ F-FDG PET/CT imaging and a review of the literature on previous instances of ectopic meningioma of the thoracic cavity diagnosed with ¹⁸ F-FDG PET/CT imaging.

A 55-year-old female patient was admitted to our hospital complaining of asthma after activity, chest tightness, and a persistent dry cough for 2 months. A physical examination of the left side of the chest revealed decreased respiratory motion, decreased breath sounds, and turbid percussion in the left side of the chest. After admission, routine blood tests, lung cancer tumor markers and node antacid staining did not show any significant abnormalities. Pleural fluid cytopathological examination showed a small number of lymphocytes, macrophages, mesothelial cells, and no malignant tumor cells. A chest computed tomography (CT) performed a lobulated pulmonary mass with calcification in the left lower lobe, and adjacent pleural hypertrophy and adhesions. The patient underwent the ¹⁸ F-FDG PET/CT examination to clarify the diagnosis. On ¹⁸ F-FDG PET imaging (Fig. 1), the standardized uptake value (SUV) of the mass increased unevenly, with SUVmax from 4.4 to 8.1. The size of the mass is about 76 mm × 70 mm × 59 mm. And without lesions identified in other locations in his body (including nervous system and spine). The patient’s diagnosis and treatment process showed in the Table 1. Due to massive calcified lesions and mild high metabolic activity, the nuclear medicine physician considered the mass to be benign. For further diagnosis and treatment, the patient received a surgery. Intraoperative exploration revealed an 8 cm diameter calcified mass between the left lower lung and the diaphragm with adhesions to the surrounding lung tissue and the diaphragm. Subsequently, the patient underwent left thoracic adhesion, mass excision, wedge resection of the left lower lung lobe and intraoperative frozen pathological examination. Gross examination revealed a grayish-white mass measuring 9.5cmx8.4cmx5.3 cm. Microscopic examination showed mainly spindle cells, with mild cell morphology. The tumor involved the pleura with fusiform nests of cells arranged in fascicles or whorls and extensive calcification. Immunohistochemistry showed positivity for epithelial membrane antigen (EMA), progesterone receptor (PR), somatostatin receptor 2 (SSTR2), CD34, and S-100, and negativity for Desmin, STAT6, ALK(1A4), and SMA. The Ki-67 index was about 20% positive. These morphological and immunohistochemical features were suggestive of a benign PPM (WHO 1 grade) (Fig. 2).

In this paper, we reported a huge mass in the, with massive calcified lesions, and mild to moderate metabolism, the final diagnosis was benign PPM. We reviewed the literature and found that most of PPMs usually appear as isolated, round, solid, well-defined nodules or masses, with or without calcification on CT scan and exhibit mild to high metabolic activity on PET scan, and the level of SUVmax alone cannot evaluate the nature of PPMs (benign vs. malignant).