Case report of parapneumonic effusion and mesothelial subdiaphragmatic cyst: relationship or coincidence?

Introduction

Parapneumonic effusion is defined as an accumulation of exudative fluid within the pleural cavity secondary to an adjacent pneumonia. ¹ It is complicated by bacterial seeding from the lungs or, less commonly, the infradiaphragmatic area, leading to empyema. Parapneumonic effusion is more frequently encountered in boys than in girls and is more common during winter and spring. ²

According to Avansino et al., ³ empyema occurs in 1 in 150 children hospitalized with pneumonia, affecting about 3.3 per 100,000 children. ⁴ Community-acquired bacterial pneumonia, pleural effusion complicated by colonization of microorganisms, and prehospital administration of ibuprofen are associated with an increased risk of progression to empyema in hospitalized children with pneumonia. ⁵ Other less common causes of pleural empyema are intrathoracic esophageal perforation, recent surgery, chest wall injury, secondary infection of preexisting hemothorax or hydrothorax, ⁶ and, in very rare instances, seeding from the abdomen to the thorax in patients with appendiceal masses and abscesses. ⁷

Subphrenic or subdiaphragmatic collection of fluid can lead to the formation of an abscess, defined as an infected collection of pus localized in the subphrenic area and bounded superiorly by the diaphragm. ⁸ Such fluid collections can also cause pleural empyema by seeding from the infradiaphragmatic area to the pleural space. ⁷ The unique anatomical structure of the left subphrenic space, defined by the presence of the spleen, phrenicocolic ligament, lesser omentum, and cardiac notch of the stomach, leads to the tendency of subdiaphragmatic fluid collections to predominantly occur on the right side. This asymmetric distribution is attributed to the specific anatomical and physiological features of the left subphrenic region, which influence the pathogenesis and localization of intra-abdominal pathologies.^9,10 These collections commonly arise secondary to abdominal surgeries, local inflammatory processes, or hollow organ perforation, ¹¹ but they can also be primary or idiopathic. ¹² Rare cases of subphrenic collections have also been associated with mesothelial cysts, which are congenital coelomic remnants with a characteristic bilobulated appearance and extracapsular location on the side of the liver. ¹³

According to some reports, parapneumonic effusion may be associated with subphrenic collections. This association is mainly based on the theory of seeding from a subphrenic abscess and therefore bacterial translocation and infection of the pleural space, which may lead to parapneumonic effusion and subsequent empyema or vice versa. ¹⁴

It should be noted that data regarding the possible relationship between mesothelial diaphragmatic cysts and parapneumonic effusions are limited. We herein report a case of complicated parapneumonic effusion occurring independently from an incidental mesothelial subphrenic cyst in a previously healthy toddler.

Case report

This report describes a toddler with pneumonia complicated by parapneumonic effusion and a lung abscess with a subphrenic collection found to be mesothelial diaphragmatic cyst. All patient details have been deidentified, and the patient’s parents provided verbal consent to publish the case. The report was approved by the Lebanese American University Institutional Review Board. The reporting of this case conforms to the CARE guidelines. ¹⁵

The patient was admitted to our institution with mild tachypnea, a nonproductive cough, and a low-grade fever of 2 days’ duration. On admission, he was febrile at 38.2°C and normotensive, and he exhibited mild intercostal retractions. Physical examination revealed normal findings, and palpation indicated no tenderness; however, there was a notable decrease in air entry, fine crackles, and dull percussion over the affected region. The patient’s oxygen saturation was 96%. He was placed on 1 L/min of supplemental oxygen by a nasal cannula. Initial laboratory evaluation results were consistent with leukocytosis (white blood cell count, 15.4 × 10³ g/dL) with a left shift (neutrophils, 84%) and reactive thrombocytosis. His C-reactive protein concentration was elevated (15.8 mg/dL), and COVID-19 real-time polymerase chain reaction was negative.

A chest radiograph (Figure 1) showed confluent infiltrates in the right mid and lower lung fields suggestive of a consolidative process. The patient began treatment with ceftriaxone at 50 mg/kg twice daily. Despite antibiotics and antipyretics, the fever persisted, peaking every 4 hours (maximum of 39.5°C). The fever was accompanied by increased respiratory efforts and an increase in the oxygen requirement to 2 L, administered by a nasal cannula. On auscultation, a significant decrease in breath sounds was noted in the right lower and middle lobes. Another chest radiograph 2 days later showed a large loculated pleural effusion with diffuse air space opacities within the right lung. Chest ultrasound performed the same day showed a loculated fluid effusion in the right hemithorax, with a thick echogenic content and an associated subphrenic encysted anechoic fluid collection that appeared lobulated and contained thin septations.

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Figure 1.

Chest radiograph upon admission. A chest radiograph in the emergency department showed confluent infiltrates in the right mid and lower lung fields suggestive of a consolidative process.

Chest computed tomography (CT) showed a large right loculated pleural effusion reaching a maximal thickness of 4.7 cm and showing loculated air–fluid levels, consistent with an abscess. The CT scan also showed associated loculated right subphrenic encysted fluid collections abutting segment VII, the largest measuring 5.1 × 2.4 cm (Figure 2). Vancomycin was administered at 20 mg/kg every 6 hours in addition to the ceftriaxone. Consent for treatment was obtained. One day later, the interventional radiology team was consulted. The right empyema and abscess were drained using a vascular needle guided by sequential CT images. Gas and pus were drained, a chest tube was inserted, and samples from the drained fluid were sent for culture and analysis. The pleural fluid analysis revealed elevated levels of pleural lactate dehydrogenase (LDH) at 27,460 U/L and pleural protein at 45 g/L, resulting in high ratios when compared with serum LDH (284 U/L) and serum protein (57 g/L) [LDH ratio of 96.69 (exceeding 0.6) and protein ratio of 0.789 (exceeding 0.5)]. The pleural LDH level surpassed two-thirds of the serum LDH, and the pleural protein level was higher than 30 d/L. All of these findings were consistent with an exudative effusion according to the modified Light’s criteria. ¹⁶ Upon a review of the literature, and after discussion with the pediatric pulmonologist, radiologist, and interventional radiologist, there was no compelling evidence to drain the cyst at that time because there was no visible connection or diaphragmatic rupture to explain the association of both entities. Hence, we decided to clinically monitor the patient and focus on the initial pleural effusion.

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Figure 2.

Right loculated pleural effusion. (a) The sagittal view showed right loculated pleural effusion with a maximal thickness of 4.7 cm and loculated air–fluid levels. An associated loculated right subphrenic encysted fluid collection was also present, measuring 5.1 × 2.4 cm and (b) Axial view of the pleural effusion with the right subphrenic collection.

One day after drainage, the patient began to improve clinically and hemodynamically. The fever was less frequent with an 8- to 12-hour interval, and the patient showed better oral intake and physical activity. Repeated blood tests showed a decrease in the white blood cell count and C-reactive protein level.

Two days after drainage, a chest radiograph revealed a significant decrease in the size of the loculated pleural effusion. After completing a full course of ceftriaxone (21 days) and vancomycin (14 days), the chest tube was removed and the patient was discharged home on clindamycin and cefuroxime for an additional 2 weeks. The chest tube remained in place for 14 days. Two months later, a repeated CT scan (Figure 3) showed clear lung parenchyma with interval resolution of the previously seen right empyema and fluid collection. A persistent subphrenic fluid lobulated cyst measuring 5.4 × 2 cm was still present, suggesting a mesothelial diaphragmatic cyst.

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Figure 3.

Interval resolution of the previously seen right empyema and fluid collection. (a) The sagittal view showed clear lung parenchyma with interval resolution of the previously seen right empyema and fluid collection and (b) The axial view showed resolution of the right empyema. The subphrenic fluid lobulated cyst was still present, measuring 5.4 × 2 cm and suggestive of a mesothelial diaphragmatic cyst.

Discussion

We have herein described a patient with pneumonia complicated by parapneumonic effusion and a lung abscess, which were successfully managed by drainage under CT guidance.

The initial imaging examination revealed a subphrenic collection. Serial imaging, including ultrasound and CT, was thus performed to determine the type and origin of this collection, whether it was benign or malignant, and whether it was related to the parapneumonic effusion by seeding or was incidental or congenital in origin. The collection was first presumed to be infectious in nature because it was seen in the context of a lung abscess. However, its lack of change in response to antibiotics and its asymptomatic course caused us to rule out a communicated abscess. We thus considered the possibility of an incidental cyst that may be congenital in origin, known in the literature as a congenital mesothelial diaphragmatic cyst. Furthermore, the radiological findings of a lobulated well-circumscribed infradiaphragmatic cystic structure with an anechoic content and without evidence of wall thickening or air–fluid or fluid–fluid levels were pathognomonic findings of a diaphragmatic mesothelial cyst.

Several documented cases of diaphragmatic mesothelial cysts have shown radiologic characteristics similar to those observed in our case. These cysts are typically right-sided, presenting as a cystic mass located between the thoracic wall and the posterolateral aspect of the right liver lobe,^17,18 and they often exhibit a bilobulated or oval shape with thin walls. ¹⁹ Our patient’s presentation is remarkable because the incidence of primary subphrenic abscess is not known and is thought to be very rare. The incidence was reported to be 13% in one case series. ²⁰

Because of its rarity, difficulties determining its exact anatomic location, and the absence of pathologic evidence, a diaphragmatic mesothelial cyst may be misdiagnosed as an intrahepatic simple cyst, a hydatid cyst, or any other cystic lesion that can be located under the diaphragm, such as a bronchogenic cyst or teratoma.

Although diaphragmatic mesothelial cysts can be removed surgically and percutaneously, they can also be monitored with consistent radiologic follow-up. When such cysts are incidentally found, the correlation between clinical findings and radiologic characteristics is the key to preventing invasive procedures. The indications for treatment of mesothelial diaphragmatic cysts have not been thoroughly described in the literature. Follow-up using periodic sonographic examinations is key to effective management. However, for complicated cysts such as those with secondary infections or those requiring prompt pain intervention, percutaneous ethanol sclerotherapy is preferred over surgery because of the potential complications and lower success rate of surgery. Ethanol is usually selected as the sclerosing agent because of its established efficacy and safety in treating liver, kidney, and spleen hydatid cysts and lymphoceles. ¹³ In our case, a follow-up scan 1 month after the parapneumonic effusion had completely resolved revealed that the subphrenic cyst had not changed in size. Therefore, we believe that lesions with this pattern should be treated conservatively with periodic sonographic monitoring. If treatment is required, percutaneous intervention should be used first because it serves both diagnostic and therapeutic purposes.