Pulmonary sclerosing pneumocytoma (PSP), formerly known as pulmonary sclerosing hemangioma, is a rare pulmonary tumor initially described by Liebow et al(2). in 1956, as a tumor with marked sclerosis and vascularization. PSP is usually seen in female over 50 years old, and most of them are single nodules. In the 2015, the World Health Organization (WHO) classification “miscellaneous tumors” was changed to “adenomas”(3). The essential feature of PSP is the presence of cuboidal surface cells and round stromal cells, which consist of four major histological patterns; hemangiomatous, papillary, sclerotic, and solid(3). The immunohistochemical staining pattern is positive for TTF-1 and EMA(4). Our case is a 20-year-old young man with bilateral multiple PSP, which has rarely been reported.
Over the last years, many studies have discussed the origin, differential diagnosis, potential malignancy and best treatment option for PSP. For many years, in fact, this tumor was presumed to be of vascular origin. Instead, immunohistochemical results, in particular the TTF-1 expression, confirm its epithelial origin from the respiratory epithelium(4). Because of the unspecific radiological features mimicking malignancies and its histological heterogeneity, the differential diagnosis with adenocarcinoma and carcinoid tumors is still challenging. Patients are usually asymptomatic and it is detected incidentally. Chest CT scan usually reveals a round, solitary, well-circumscribed, homogeneous nodule and FDG PET/CT scan usually reveals a low to moderate uptake in PSPs(5). Our patient also had no clinical symptoms, and chest CT and PET-CT findings were similar to those reported in the literature. From the imaging inferences, the pulmonary nodules of the patient were considered benign first. We also performed fine-needle aspiration (FNA) cytology on the largest nodules, but no evidence of malignant tumor was found. Therefore, we followed the patient for 6 months, and found that the pulmonary nodules had a tendency to slowly grow larger. In view of this situation, we decided to perform surgical treatment for the patient. Pre-operative diagnosis, when feasible, is helpful to plan the best therapeutic strategy. Gal et al. was the first to report that the cytologic diagnosis of PSP requires the identification of its dual cell population, made up of abundant stromal cells and fewer surface cells(6). The problem is that fine-needle aspiration (FNA) cytology is poorly diagnostic, both due to the rarely distinct separation of the two tumor cell types in the specimen and to the disease rarity and hence potential unfamiliarity with its cytologic features of most pathologists. Preoperative cytologic and histological findings of PSP are limited to few case reports, in which computed tomography (CT)-guided FNA, EBUS-TBNA or intraoperative frozen sections (FS) often led to misdiagnosis(7). In our case, intraoperative frozen section suggested PSP coexisting with adenocarcinoma, but immunohistochemical results revealed that all nodules were sclerosing alveolar cell tumor. PSP combined with lung adenocarcinoma has indeed been reported in very few reports(8, 9). PSP can also be combined and admixed with other lung tumors, such as mucinous adenomatous hyperplasia(10), glandular papilloma (GP)(11), pulmonary spindle cell carcinoma (PSCC)(12), extensive neuroendocrine lesions (including pulmonary neuroendocrine cell hyperplasia, multiple carcinoid tumorlets and typical carcinoid tumors within one pulmonary lobe)(13). FNA cytology is poorly diagnostic, and the misdiagnosis rate of intraoperative frozen section is also high. Shang Z et al. reports the rate of intraoperative misdiagnosis of PSP smaller than 1 cm was 11.1%(14). The pathological diagnosis of PSP is challenging, and obtaining sufficient samples and immunohistochemical examination is the key to improve the diagnosis rate.
PSP can be associated with other tumors at different sites, such as hereditary nonpolyposis colorectal cancer (HNPCC, Lynch syndrome)(15), familial adenomatous polyposis(16), retroperitoneal liposarcoma and renal carcinoma(17), multiple uterine fibromas, cysts of the thyroid and kidney(18), and endometrial stromal sarcoma(19). This indicates that other malignant tumors can coexist with multiple solid pulmonary nodules and be misdiagnosed at times as multiple pulmonary metastases, which would affect the clinical treatment decision; therefore, these masses need to be carefully identified. It has been reported that PSP may present with hilar and mediastinal lymph node metastasis and pleural dissemination(20–22). In the present case, the hilar and mediastinal lymph nodes were not significantly enlarged, and the pathological results from the hilar lymph nodes were negative.
Even with the help of enhanced CT, PET-CT, puncture biopsy or intraoperative rapid pathological reports, PSP may be misdiagnosed. Surgical resection is the treatment of choice for PSP because there have been no reports of recurrence in the literature. Lymph node dissection should be considered for huge tumors because lymph node metastases correlate with a larger tumor size(23). The chest CT of this patient revealed 7 nodules, 3 in the left lobe and 4 right. We resected all the nodules through two surgeries, and the patient recovered smoothly each time. We will perform a long follow-up to assess recurrence and metastasis for this patient.