A Sheep in Wolf’s Clothing: Pulmonary Sclerosing Pneumocytoma Mimicking Malignant Neoplasm

Abstract

Pulmonary sclerosing pneumocytoma, a rare pulmonary adenoma, is a diagnostic dilemma because of its vague symptoms, ambiguous radiologic features, and varied histopathologic findings, leading to errors in diagnosis and management. We report a case manifesting with a picture of an aggressive malignant neoplasm that postoperatively proved to be benign. This patient presented with a large intrathoracic mass encompassing the pulmonary vessels in the hilum and extending to the posterior mediastinum. After extensive investigations, operability appeared to be a challenge. Complete surgical resection assisted by cardiopulmonary bypass led to a curative outcome. This rare presentation highlights the deceptive nature of pneumocytomas.

Pulmonary sclerosing pneumocytoma (PSP), previously termed pulmonary sclerosing hemangioma, has been classified as a pulmonary adenoma by the World Health Organization since 2021.¹ This case describes an unusual presentation in a young Indian woman with a large tumor exhibiting features of an infiltrative, inoperable thoracic mass, later confirmed as benign after extensive surgical resection. To our knowledge, this rare presentation of a PSP has not been previously reported.

A previously healthy 23-year-old nonsmoking female patient presented with breathlessness, left-sided chest discomfort, and cough of 4 months’ duration accompanied by loss of appetite and weight. Respiratory examination revealed that she had reduced air entry on the left side. Laboratory investigations showed anaemia and thrombocytosis. Chest radiography showed complete opacification of the left hemithorax with areas of calcification (Figure 1). Contrast-enhanced computed tomography (CT) scan of the thorax showed a large mass occupying the entire left lung with areas of heterogeneous calcification. The mass completely encased the left pulmonary artery and partly surrounded the descending thoracic aorta (Figure 2).

Figure 1.

Chest radiograph showing complete opacification of left hemithorax with areas of calcification. (L, left.)

Figure 2.

(A) Mass showing complete encasement of the left pulmonary artery and surrounding the descending thoracic aorta. (B) Avid fluorodeoxyglucose uptake on positron emission tomography/computed tomography with a maximal standardized uptake value of 14.5.

Positron emission tomography CT scan showed avid fluorodeoxyglucose uptake with a maximum standardized uptake value of 14.5 (Figure 2). Ultrasound-guided biopsy reported a spindle cell tumor or an inflammatory myofibroblastic tumor. It did not show malignant changes.

The size of the mass, vascular encasement, and high fluorodeoxyglucose uptake led us to believe it was a malignant mass, and it was considered most likely to be inoperable. However, given her young age and the absence of confirmed malignancy on biopsy, it was decided to attempt to debulk the tumor. A left pneumonectomy was performed under cardiopulmonary bypass because of the proximity of the mass to the pulmonary artery and aorta. The patient was cannulated, and cardiopulmonary bypass was initiated; arterial cannulation was done in the descending thoracic aorta and venous cannulation in the main pulmonary artery. A left posterolateral thoracotomy approach was employed, with tumor dissection performed in an encircling manner to ensure hemostatic control of the feeder vessels. A technically challenging surgery achieved complete resection of the mass. Tumor invasion of the pulmonary artery wall necessitated bovine pericardial patch repair of the main pulmonary artery. The patient’s immediate postoperative recovery was uneventful, and she was discharged on postoperative day 7.

The 16 × 13 × 8-cm lesion’s cut section was gray-brown. Microscopic examination showed focal central hyalinization with dystrophic calcification and tumor cells in solid sheets with individual cells spindled out with a sclerotic stroma (Figure 3). On immunohistochemistry, epithelial membrane antigen and thyroid transcription factor 1 were positive in tubular cells. Vimentin was positive and Ki67 proliferation index was 5%. Histopathologic evaluation of the resected specimen revealed a benign PSP. No adjuvant treatment was deemed necessary in light of the benign nature of the tumor on histopathologic evaluation. Follow-up imaging over the course of 7 years showed no recurrence.

Figure 3.

Histopathologic evaluation showing tumor cells in solid sheets with individual cells spindled out with sclerotic stroma (encircle).

The patient had complete symptomatic relief. From a distressing diagnosis of an inoperable malignant neoplasm, she underwent complete resection of the tumor and was cured.

Comment

PSPs, rare pulmonary tumors, account for 0.2% to 1% of lung tumors.² PSP was first described by Liebow and Hubbell in 1956.³ Previously thought to be of vascular origin, it has now been concluded to be of epithelial origin, arising from immature type II pneumocytes or Clara cells, as described by Devouassoux-Shisheboran and coworkers.³ PSPs predominantly affect middle-aged women (40-60 years of age) in Asia.⁴ They are usually detected incidentally on routine chest radiography of asymptomatic patients. Less than 8% of patients are symptomatic.³ Our patient experienced chest pain from compression by a large mass.

On CT scan, PSPs typically appear as isolated, peripheral, well-defined masses or nodules with smooth margins, which may be accompanied by calcification and cystic degeneration.⁵ A meta-analysis by Zhang and coworkers⁶ reported that only 13% of patients with benign pneumocytomas had tumors ≥50 mm, but none exceeded 100 mm. In contrast, our case was a benign tumor significantly larger than this (160 mm). Whereas most PSPs exhibit a low to moderate uptake on positron emission tomography scan, our case showed a high standardized uptake value of 14.5, probably because of its large size.⁷

Diagnosis of PSPs by small biopsy specimens is challenging. In our case, on ultrasound-guided biopsy, the specimen was initially misdiagnosed as a spindle cell tumor or an inflammatory myofibroblastic tumor. Iyoda and coworkers⁸ reported that only 27% of patients with pneumocytoma were accurately diagnosed preoperatively through percutaneous needle or transbronchial biopsy, highlighting the need for larger specimens to be retrieved.

PSPs exhibit 4 distinct growth patterns: solid, sclerotic, papillary, and hemangiomatous.³ On histopathologic examination, they predominantly show 2 types of cells, cuboidal surface cells and round to polygonal stromal cells, both of which have different staining characteristics. Both types of cells stain positive for thyroid transcription factor 1 and epithelial membrane antigen, with cuboidal cells also positive for napsin A and cytokeratin.² Without immunohistochemistry, PSP may be misdiagnosed as a well-differentiated adenocarcinoma or carcinoid tumor.⁴ Our patient’s histopathologic findings were consistent with these characteristics.

Thoracoscopic resection is the primary treatment of PSPs; given the benign nature of most PSPs, mediastinal lymph node dissection is largely not necessary.⁴ In a meta-analysis of PSPs, surgical resections described were mainly lobectomies and limited lung resections, and only 1 patient in that meta-analysis required a pneumonectomy.⁶ Our patient again is one of the rare patients for whom a pneumonectomy was deemed necessary with assistance of cardiopulmonary bypass, a rare approach that to our knowledge has not been described earlier. The prognosis after PSP resection is generally favorable.⁴ Our patient had a remarkable outcome and showed no recurrence on imaging 7 years after surgery. Recurrence is extremely rare and is typically attributed to incomplete initial resection.³

It is important that this rare entity be kept in mind when a patient presents with a large thoracic mass. Despite their ominous appearance, such masses may be benign, as in this case, and complete surgical resection can achieve a cure.