Wolf in sheep’s clothing: a case of primary lung adenosquamous carcinoma mimicking traumatic pulmonary pseudocyst

Abstract

Background

Traumatic pulmonary pseudocyst is a rare “cystlike” lung lesion that typically develops following blunt chest trauma. It differs from lung cancer associated with cystic airspaces in terms of pathogenic mechanisms, clinical manifestations, and radiological features. Furthermore, there are few reports of the diagnostic bias between traumatic pulmonary pseudocyst and lung cancer associated with cystic airspaces. Here, we present a rare case of lung cancer associated with cystic airspaces that mimicks traumatic pulmonary pseudocyst.

Case presentation

A 61-year-old man with no chest medical or surgical history, no chest radiologic examination within the last five years, and no smoking history had an air-filled “cystlike” lesion surrounded by solid components and ground-glass opacities in the middle third of the right upper lobe of the lung during a computed tomography evaluation following blunt chest trauma. He was initially diagnosed with traumatic pulmonary pseudocyst and treated conservatively. On the third post-trauma day, he experienced hemoptysis, which was successfully treated with intravenous hemostatic medication. On the ninth post-trauma day, he exhibited a significant hemoptysis and a moderate dyspnea. A subsequent chest computed tomography scan demonstrated that the solid components had entered the lesion’s cavity and significantly expanded, and the surrounding ground-glass opacities had slightly enlarged. A contrast-enhanced chest computed tomography scan and a three-dimensional reconstruction computed tomography image confirmed that the solid components were a hematoma caused by damage to the right upper pulmonary vein. A right upper lobectomy was performed based on the concern about severe intrapulmonary bleeding. An intraoperative frozen section analysis showed significant bleeding in the lung parenchyma. Adenosquamous carcinoma was unexpectedly identified during the postoperative pathological examination of the resected specimen. A diagnosis of primary lung adenosquamous carcinoma was made. He was discharged on the seventh postoperative day and followed up for two years without any recurrence.

Conclusions

The potential of lung cancer associated with cystic airspaces should be considered for “cystlike” lung lesions discovered in elderly patients after blunt chest trauma. A comprehensive review of the medical history, meticulous analysis of the radiological findings, and close monitoring can help clinicians reduce the risk of diagnostic bias.

Background

Traumatic pulmonary pseudocyst (TPP) is a rare “cystlike” lesion of the lung that typically appears as an air- or fluid-filled space in the pulmonary parenchyma without an epithelial lining [1]. It is generally detected on chest computed tomography (CT) scans for trauma evaluation following blunt chest trauma [2]. In blunt chest trauma, TPP results from disruption and laceration of the lung parenchyma caused by increased intrapulmonary pressure and/or shearing forces, which subsequently leads to the formation of an air-filled space when the elastic tissue of the lung retracts [3]. Damage to pulmonary capillaries or minor vessels frequently results in the formation of hemorrhagic edema of the alveoli and interstitium around the TPP. The space appears an air-fluid level when blood enters and alters to be blood-filled when the entire space is filled with blood and the air is completely absorbed. Hemoptysis and dyspnea may result from persistent bleeding into the space and pulmonary contusion. Lung cancer associated with cystic airspaces (LCCA) is characterised by the presence of single or multiple airspaces on CT scans, with associated consolidation and/or ground glass components [4]. It is notable that the airspaces always exhibit a lack of an air-fluid level. A number of mechanisms have been proposed to elucidate the formation of airspaces in LCCA. These include the check-valve effect, which obstructs the small airways; the development of cancer along the wall of a pre-existing bulla; and the expectoration of central necrotic tissue [5,6,7]. It is possible that more than one mechanism may exist. Given the distinct differences in pathogenic mechanisms, clinical manifestations, and radiological features between TPP and LCCA, there should theoretically be no confusion between the two conditions. Indeed, there are few reports in the literature of the diagnostic bias between TPP and LCCA. Nevertheless, we did encounter a rare case of LCCA that mimicked TPP.

Case presentation

A 61-year-old man was admitted to our hospital one day after being involved in a car accident. He only reported experiencing severe right chest pain. He had no chest medical or surgical history, no chest radiologic examination within the last five years, and no history of smoking. On admission, a chest CT scan revealed the presence of an air-filled “cystlike” lesion in the middle third of the right upper lobe of the lung, surrounded by solid components and ground-glass opacities, without sternal or rib fractures (Fig. 1A). The patient was initially diagnosed with TPP and treated conservatively. On the third post-trauma day, he experienced hemoptysis, which was successfully managed with intravenous hemostatic medication (a combination of etamsylate, aminomethylbenzoic acid, and vitamin K1). On the ninth day following the trauma, he exhibited a significant hemoptysis and a moderate dyspnea. A subsequent CT scan of the chest revealed that the volume of the cavity had not changed considerably, but that the solid components had entered the cavity and significantly expanded, and that the surrounding ground-glass opacities had slightly enlarged (Fig. 1B). The solid components were confirmed to be a hematoma due to injury to the right upper pulmonary vein on a contrast-enhanced chest CT (Fig. 2A) and a three-dimensional reconstruction CT image (Fig. 2B). Given the concern about severe intrapulmonary bleeding, he underwent a video-assisted thoracoscopic right upper lobectomy. An intraoperative frozen section analysis showed significant bleeding and infiltration of inflammatory cells in the lung parenchyma. Surprisingly, the postoperative pathological examination of the resected specimen demonstrated adenosquamous carcinoma (Fig. 3). The diagnosis of primary lung adenosquamous carcinoma (T1aN0M0, stage IA1) was confirmed based on the TNM staging (8th edition). Following a period of uncomplicated postoperative recovery, he was discharged on the seventh postoperative day. He was followed up for two years, during which no recurrences were observed.

Fig. 1

Chest computed tomography shows (A) an air-filled “cystlike” lesion in the middle 1/3 of the right upper lobe that was surrounded by solid components and ground-glass opacities, and (B) the solid components had entered the cavity and drastically grown, and the surrounding ground-glass opacities had slightly enlarged

Fig. 2

Contrast-enhanced chest CT (A) and three-dimensional reconstruction CT image (B) shows right upper pulmonary vein bleeding

Fig. 3

Histological analysis revealed significant heterotypic cell nests, with cells grouped in a solid and adenoid structure, by hematoxylin and eosin staining (×200)

Discussion and conclusions

In the present case, a “cystlike” lung lesion was detected during a CT evaluation following blunt chest trauma. Subsequent serial chest CT scans demonstrated a rapid progression of the lesion’s cavity from an air-filled to a blood-filled pattern, accompanied by a growing exacerbation of the surrounding hemorrhagic edema. These findings were consistent with the radiological characteristics of TPP evolution and almost masked the distinctive features of LCCA, which like a wolf in sheep’s clothing. Consequently, the initial diagnosis was incorrect, with LCCA being misidentified as TPP. To the best of our knowledge, only Kamiyoshihara et al. [8] have reported a case of primary lung cancer in a young adult who was initially misdiagnosed as TPP. In this case, the patient sustained multiple rib fractures and a clavicle fracture on the left side following a traffic accident, and a “cystlike” lung lesion was identified in the right lower lobe. The authors concluded that the misdiagnosis was due to the suspicion of a contracoup injury, the insufficient medical history, and the belief that lung cancer was rare in young individuals.

Despite the fact that the patient in the present case underwent a lobectomy following a diagnosis of TPP, TPPs are typically self-resolving without the need for specific treatment [3], with the exception of potential life-threatening complications. In contrast, for LCCAs, more aggressive treatment is necessary, and early intervention is associated with potentially curative outcomes. Therefore, it is essential to identify the wolf in sheep’s clothing early and accurately among the flock. In order to minimize the potential for diagnostic bias in similar cases, it is important to note several key points.

Firstly, an accurate diagnosis frequently commences with a comprehensive medical history review, and a negative history associated with a “cystlike” lung lesion prior to trauma will prompt clinicians to consider TPP more. The majority of TPPs occur in children and young adults under the age of 30, due to their more flexible chest walls [9, 10]. The average age at LCCA diagnosis ranged from 58.3 to 70.6 years old [7, 11,12,13]. Consequently, the “cystlike” lung lesion found in elderly individuals following chest trauma should not be immediately diagnosed as TPP, nor should LCCA be readily ruled out in the absence of a comprehensive medical history review.

Secondly, the presence of typical chest CT features consistent with a definite chest trauma is an essential indicator for TPP. TPPs can be observed on CT within 48 h following trauma in any lung lobe [2, 9]. The majority of these lesions appear as air-fluid levels, with the lower lobe being more frequently involved than the upper due to the lower chest wall’s greater pliability [9, 10]. It is possible that peripheral TPPs may be predominantly detected in the immediate region of chest wall injury, while central TPPs may primarily be found in the area of contracoup injury [14]. Moreover, it is notable that almost all TPPs are accompanied with lung contusions, with the majority also accompanied with rib fractures. Nevertheless, the presence of LCCAs is not associated with a predilection for any particular lobe, and they are not accompanied with pulmonary contusion. Furthermore, they rarely manifest as an air-fluid level in the airspace. In the context of the present case, it is postulated that the patient had an LCCA prior to the accident, and that the LCCA’s pre-existing airspace was more fragile than the alveoli. The sudden increase in intrapulmonary pressure caused by blunt chest trauma resulted in the rupture of the wall of the airspace and lung parenchyma surrounding it, leading to the occurrence of lung parenchymal hemorrhage. The consolidation and/or ground glass components of LCCA were therefore obscured by pulmonary contusion or hematoma. Consequently, the wolf was able to disguise itself as a sheep and trick the hunter initially.

Last but not least, TPPs typically resolve within a period of 1 to 6 months (averaging 3 months) [9, 10], whereas LCCAs may undergo mild morphological changes or develop into more complex lesions [4], exhibiting asymmetric wall thickening or solid nodule transformation. Any persistent or developing “cystlike” lung lesion, even if it is diagnosed as TPP, should be closely followed up until it has entirely resolved. In the event that the lesion fails to improve over time, it is necessary to reconsider the possibility that the cause may be something other than TPP. It is recommend that a CT strategy with thin-section images be implemented at 3, 6, and 12-month intervals for follow-up.

In conclusion, it is important to note that LCCAs may resemble TPPs in radiological features and may imitate the evolution of TPPs following blunt chest trauma in elderly individuals, which may result in them be mistakenly labeled as TPPs. A comprehensive review of the patient’s medical history, meticulous analysis of the radiological findings, and close monitoring can help clinicians reduce the risk of misdiagnosis.