Primary pulmonary meningioma

Primary pulmonary meningioma (PPM) is a rare tumor and only sporadic cases have been reported. Here, we report a case with complete clinical procedure and imaging data including chest radiography, preoperative CT, CT‐guided biopsy, and postoperative pathological results.

A 66‐year‐old male was found to have an incidental left lung nodule on chest radiography following a traffic accident. Chest CT revealed a 3.0 × 1.9 × 2.3 cm solid nodule with a well‐circumscribed margin and slightly homogeneous enhancement in the lower lobe of the left lung. (Figure 1A) CT‐guided biopsy suggested a provisional diagnosis of low‐grade epithelioid tumor positive for EMA and negative for SSTR2A in immunohistochemistry. For pathological confirmation, video‐assisted thoracoscopic lobectomy of the lower lobe of the left lung was performed under the impression of stage IB(T2aN0M0) non‐small cell lung cancer with visceral pleural invasion. Macroscopically, the tumor manifested as a yellowish‐white and well‐circumscribed firm nodule; while microscopically, it was composed of meningothelial‐like cells and spindle‐shaped cells arranged in whorl and fascicular patterns. Immunohistochemical stains were positive for EMA and SSTR2A. (Figure 1B–D) The results of tests for CK, CD34, STAT6, and TLE were negative. Negative staining was used to differentiate PPM from solitary fibrous tumor and synovial sarcoma. There was no malignant feature. As postoperative brain MRI revealed negative findings, this case was diagnosed as a benign PPM. No tumor recurrence was observed in the one‐year follow‐up CT study.

FIGURE 1.

(A) CT axial imaging showed a well‐circumscribed solid nodule in the lower lobe of the lung. (B) Histological features of the case, primary pulmonary meningioma (PPM) showed as meningothelial‐like cells and spindle‐shaped cells arranged in a focal whorl pattern and fibroblastic patterns on hematoxylin–eosin (H&E) staining (100×). (C) In immunohistochemistry study, the tumor cells showed positive staining for epithelial membrane antigen (EMA) (400×) and (D) Somatostatin Receptor 2 (SSTR2) (400×).

PPMs are extremely rare. A total of 70 patients (including our case) have been diagnosed with PPM and reported in the English literature. ¹ , ² Most PPMs are benign (0.4–6.5 cm in diameter), but five malignant PPMs (1.5–15 cm) have been reported. Radiologically, a PPM typically presents as an isolated, well‐defined solid nodule ¹ ; however, some PPMs may present as ground‐glass density nodules or multiple solid nodules. ¹ , ³ PPMs have various enhancement CT manifestations, and the pattern of lesion enhancement might not help to determine whether the PPM is benign or malignant. On ¹⁸F‐FDG PET, most PPMs exhibit high or slightly high metabolic activity, but four PPMs showed low uptake of ¹⁸F‐FDG. ¹ Additionally, one recent study reported increased glucose uptake in synchronous benign and malignant PPMs. ⁴ This result suggested that the malignancy of PPM might not be correlated with ¹⁸F‐FDG uptake.

Some PPM patients have a known history of malignancy ¹ so a comprehensive and careful evaluation of pulmonary lesions must be carried out to differentiate between primary lung lesions and metastasis. Additionally, it is difficult to distinguish PPM from other lung tumors through radiological findings only, pathological examination for the suspicious lesion is important for the diagnosis of PPM. Histologically, the tumor cells are arranged in sheets, whorls, or onion peel‐like formations. Immunohistochemistry manifested tumor cell positivity for SSTR2A, EMA, and PR, and negative for STAT6 and SOX as is the characteristic of a meningioma. ⁵ Solitary fibrous tumor, synovial sarcomas, and schwannoma are the diseases that should be considered in the histopathlogical differential diagnosis of PPMs. Solitary fibrous tumor reveals positive for STAT6. Synovial sarcomas show positive for SSTR2A, EMA, and ILA. Schwannoma reveals positive for SOX10 and negative for SSTR2A. However, the immunohistochemical profile of meningioma might be overlapped with other entities such as solitary fibrous tumor. ⁵ Our case was misdiagnosed as having a low‐grade epithelioid tumor positive for EMA and negative for SSTR2A based on CT‐guided biopsy. It was worth reviewing that this case was not sent a frozen section before lobectomy. This tumor was peripheral. A wedge resection might replace lobectomy if a benign PPM was diagnosed on frozen section before lobectomy. Diagnosis of a PPM relies on the presence of the tumor in the lungs and exclusion by a meningioma in the CNS. Surgical resection of PPM is the treatment of choice, and no relapse has been reported in benign cases after complete resection.

CONFLICT OF INTEREST

The authors declare no conflict of interest.