Magnetic resonance imaging findings of pulmonary sclerosing pneumocytoma: a case report and literature review

Abstract

Background: Pulmonary sclerosing pneumocytoma (PSP) is a rare lung tumor that is mostly isolated and commonly reported among middle-aged East Asian women. Recently, Immunohistochemistry (IHC) analysis has suggested that PSP is of primitive epithelial origin, most likely derived from type II alveolar air cells. Patients with PSP are generally asymptomatic and usually detected for other unrelated reasons during routine imaging. Several studies have already investigated the computed tomography (CT) features of PSP and their correlation with pathology. Magnetic resonance imaging (MRI) is a radiation-free imaging technique with important diagnostic value for specific pulmonary nodules. However, very few case reports or studies focus on the MRI findings of PSP.

Case report: We reported a case of an asymptomatic 56-year-old female with a solitary, well-defined soft-tissue mass in the lower lobe of the left lung. The mass showed iso-to-high signal intensity (SI) than muscle on T1-weighted image (T1WI) and T2-weighted image (T2WI) and a much higher SI on fat-suppressed T2WI, diffusion-weighted image, and apparent diffusion coefficient image. Contrast-enhanced fat-suppressed T1WI revealed noticeable inhomogeneous progressive enhancement throughout the mass. The mass revealed early enhancement without a significant peak, followed by a plateau pattern on dynamic contrast-enhanced MRI images. The patient underwent left basal segmentectomy via thoracoscopic surgery. Histopathology and IHC results of the surgical specimen confirmed that it was a PSP. We concluded that the MRI findings of PSP might adequately reflect the different components within the tumor and aid clinicians in preoperative diagnosis and assessment. To the best of our knowledge, this is the most comprehensive case report on the MRI findings of PSP.

Conclusion: The MRI findings of PSP correspond to its histopathological features. Here, we present a case of PSP with the most comprehensive MRI findings, emphasizing the importance of multiple-sequence MRI in diagnosing PSP.

Keywords: case report; computed tomography; magnetic resonance imaging; pulmonary; pulmonary sclerosing pneumocytoma.

Figure 1

Axial pre-contrast CT image (mediastinal window setting) (A) revealed a solitary well-defined soft-tissue mass in the size of 3cm×3 cm×3 cm, with some low-attenuation areas in the lower lobe of the left lung. Axial arterial phase CECT image (mediastinal window setting) showed a heterogeneous and obvious enhancement of the mass, with multiple focal areas of marked enhancement visible within the tumor (B). Axial venous phase CECT image (mediastinal window setting) showed further enhancement of the mass with irregular multiple focal low-attenuation areas internally (C). Axial lung window setting image showed a clear interface between the tumor and the lung, with unremarkable low-attenuation visible in the distal lung tissue (arrow) (D). The coronal CECT images in the mediastinal window setting (E) and lung window setting (F) showed that the tumor margin closely compressed the adjacent pulmonary artery and vein branch vessels.

Figure 2

Axial in-phase T1WI image (A) and out-phase T1WI image (B) showed a round mass with iso-to-high SI compared with the thoracic muscle and mixed with some low SI foci within the mass. On the out-phase T1WI image, no areas of obvious signal reduction were found within the tumor compared to the in-phase T1-weighted image. On axial T2WI image (C), the tumor showed iso-to high SI with some small low SI foci, while on axial fat-suppressed T2WI image (D), the tumor showed a much higher SI. On axial DWI image (E) and ADC image (F), the mass showed a much higher SI, and the ADC value was (2.36 ± 0.22)×10^-3mm²/s, suggesting that the mass was a benign tumor. DCE-MRI images (G) and corresponding time intensity curve of the SI (H) after intravenous injection of Gd-DTPA show early enhancement without obvious peak point, and subsequent plateau pattern.

Figure 3

Histopathology of the present case of PSP. It was composed of four major histologic patterns: (A) solid pattern (20%, Hematoxylin and eosin, ×20), (B) papillary pattern (10%, Hematoxylin and eosin, ×20), (C) sclerotic pattern (40%, Hematoxylin and eosin, ×20), and (D) hemangiomatous pattern (30%, Hematoxylin and eosin, ×20).

Figure 4

Immunohistochemical results. Immunohistochemical staining (×20) showed that the cuboidal surface cells and round stromal cells the of the tissue are positive for thyroid transcription factor-1 (TTF-1) (A), epithelial membrane antigen (EMA) (B) and Vimentin (C). AE1/AE3 was positive in cuboidal surface cells but negative in round stromal cells (D), while progesterone-receptor (PR) exhibited a negative result in cuboidal surface cells but a positive result in round stromal cells (E). The Ki-67 index was below 2% (F).