We are presenting a teenage girl with a recent history of virilism who presented with tension pneumothorax. Subsequent contrast-enhanced chest CT revealed multiple bilateral irregular thin-walled cysts of varying sizes with numerous solid noncalcified pulmonary nodules and pulmonary artery pseudoaneurysms. Lung biopsy revealed trophoblastic neoplasm with metastasis to both lungs. We discussed the differential diagnosis of diffuse cystic lung diseases. While diffuse cystic lung diseases in children are rarely due to malignancy, we emphasize that clinicians be aware of the possibility of metastatic lung diseases and their radiologic features when encountering diffuse cystic lung diseases.

Late Development of Pneumatoceles in Necrotizing PneumoniaSila Y. Kocer 1, Nathan C. Hull MD2, D. Dean Potter, Jr. MD 3, Theresa Madigan MD 4, Jennifer M. Boland MD5 and Nadir Demirel MD 61Ondokuz Mayis University School of Medicine, Samsun, Turkey2Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA. Email address: [email protected] of Pediatric Surgery, Department of Surgery, Mayo Clinic, Rochester, Minnesota, USA. Email address: [email protected] of Pediatric Infectious Diseases, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, Minnesota, USA. Email address: [email protected] of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota, USA. Email address: [email protected] of Pediatric Pulmonology, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, Minnesota, USA. Email address: [email protected] : Sila Y. Kocer, Ondokuz Mayis University School of Medicine, Körfez, 55270 Samsun, Turkey. Email address: [email protected]. Tel.: +905514571963Conflict of interest: The authors declare no conflict of interest.Author contributions : Sila Y. Kocer: Writing – original draft. Nathan C. Hull: Writing – review and editing.D. Dean Potter Jr.: Writing – review and editing.Theresa Madigan: Writing – review and editing.Jennifer M. Boland: Writing – review and editing.Nadir Demirel: Writing – review and editing.Keywords : Lung cysts; complicated pneumonia; lobectomy; imaging; childrenTo the editor,Community-acquired pneumonia (CAP) is one of the most common serious infections in children, although it usually has a good prognosis1. Necrotizing pneumonia (NP), a rare but severe complication of CAP, consists of the destruction of the consolidated lung parenchyma, potentially leading to the formation of thin-walled cavities known as pneumatoceles 2. While they often resolve spontaneously without sequalae, progressively enlarging pneumatoceles have been reported 5. We report a pediatric case with an unusual course of pneumatocele development.A 3-year-old female with history of congenital hypothyroidism and mild asthma presented to her primary care physician for evaluation of intermittent fever for the past 6 days, with a maximum temperature of 38.8°C. She had a worsening wet cough and complained of chest pain while coughing. Lung examination was normal except for mild tachypnea. Based on the patient’s presentation, empiric oral amoxicillin 90 mg/kg/day was started for possible CAP. The patient presented to the clinic on day 6 of her antibiotic treatment with persistent low-grade fever and ongoing cough. She had normal vital signs, and there were no signs of respiratory distress. The lung examination revealed crackles at right lung fields. A chest X-ray (CXR) showed a large consolidation and an airspace with an air-fluid level in the right upper lobe (RUL) (Figure 1A). There was no pleural effusion. The patient was diagnosed with complicated pneumonia and was referred to our hospital.A chest computed tomography (CT) without intravenous (IV) contrast showed a large consolidation in the RUL with scattered internal cystic areas containing air-fluid levels (Figure 1B, C). These findings raised concern for NP, abscess, or congenital pulmonary airway malformation with superimposed pneumonia. Laboratory test results showed mild anemia (hemoglobin concentration of 10 g/dl), leukocytosis (white blood cell count of 14.1 x 109/L), thrombocytosis (platelet count of 752 x 109/L), and high C-reactive protein (CRP) (80 mg/L, normal: <5 mg/L). She was admitted and started on IV ceftriaxone and IV vancomycin. She remained afebrile during admission and was clinically well appearing. A nasal swab culture for Methicillin-resistant Staphylococcus aureus was negative, therefore, on day 2 of admission, IV vancomycin was discontinued. AStreptococcus pneumoniae urine antigen test was positive. Serologic testing for endemic fungi was negative. A QuantiFERON-TB Gold was indeterminate due to inadequate mitogen response. On day 3 of admission, in preparation for discharge, IV ceftriaxone was switched to oral cefdinir 14 mg/kg/day to complete a 4-week course. She remained afebrile and well after an additional 24-hour period of observation and was subsequently discharged.Towards the conclusion of her antibiotic course, a follow-up CXR showed near resolution of the RUL consolidative opacity with a few small residual lucencies in the RUL, presumed to be residual pneumatoceles (Figure 1D). She was asymptomatic without a cough, and her lung examination was normal. Inflammatory markers, including CRP and sedimentation rate, as well as white blood cell count and platelet count, were in the normal range. One month later, while the patient remained asymptomatic, a follow-up CXR revealed an enlarged pneumatocele (Figure 2A, B). A chest CT with IV contrast demonstrated a 7.2 x 5.3 x 7.6 cm air-filled cavity in the RUL (Figure 2C, D). No definite connection to the adjacent airways was seen on the chest CT. The patient then underwent a thoracoscopic right upper lobectomy. The procedure was challenging due to adhesions and bleeding (Figure 2E). The pathology examination of the resected lung tissue showed a simple fibrous-walled cyst devoid of epithelial lining, consistent with pneumatocele (Figure 2F). Gram stain, fungal smear, bacterial culture and fungal culture of the explanted lung tissue were negative. The patient made a full recovery, both radiologically and clinically.Patients with NP usually present with symptoms of CAP, unresponsiveness to initial outpatient treatment, such as high fever, cough, tachypnea, and general unwell appearance 1. The initial treatment of NP consists of IV antibiotics covering the most common etiologic agents of NP, which are known to be S. pneumoniae , Group AStreptococci and S. aureus . The optimal duration of antimicrobial therapy is not clearly defined; however, usually prolonged with a median duration of 4 weeks reported in the literature2, which aligns with guideline suggestions for therapy of empyema and parapneumonic effusion 3. Improvement in clinical and laboratory parameters usually allows for IV to oral antibiotic transition, which was accomplished relatively early for our patient, due to her less severe initial presentation and rapid clinical improvement. Pneumatoceles, air-filled cysts that can arise as a complication of NP, typically regress over weeks to months when NP is treated, but might require segmental or lobar resection if they become tense (exceeding more than 50% of the involved lobe), infected, or rupture 1. In our patient, many of the small pneumatoceles decreased in size after antibiotic treatment, with subsequent delayed and marked enlargement of one of them. A report on giant lung cysts emerging after NP suggested that, when patients remain clinically stable, treatment of pneumatoceles should be conservative with antibiotics alone regardless of the size of the cysts, as interventional procedures carry a risk of complications such as bronchopleural fistula 4. However, a study that proposed a treatment algorithm for pneumatoceles, recommended surgical resection for those that remained unresolved despite a conservative approach and gradually grew in size and wall thickness5. Our patient had no symptoms related to the pneumatocele. Nevertheless, it can be challenging to anticipate the progression of pneumatoceles, as they can enlarge enough to compromise respiration. The unusual expansion within a span of 1 month in our case, led to the decision of surgical resection.To summarize, we present a 3-year-old otherwise healthy girl with NP. After 4 weeks of antibiotic therapy, the right lung consolidations resolved and pneumatoceles decreased in size. However, one month later, while she remained clinically asymptomatic, a follow-up CXR revealed the progressive enlargement of a pneumatocele which eventually required surgical resection. Based on this experience, we suggest a close radiological follow-up of patients with post-infectious pneumatoceles, regardless of symptoms, until complete radiologic resolution is demonstrated.References1. de Benedictis FM, Kerem E, Chang AB, Colin AA, Zar HJ, Bush A. Complicated pneumonia in children. Lancet. 2020;396(10253):786–798. doi:https://doi.org/10.1016/s0140-6736(20)31550-62. Masters IB, Isles AF, Grimwood K. Necrotizing pneumonia: an emerging problem in children? Pneumonia (Nathan). 2017;9(1). doi:https://doi.org/10.1186/s41479-017-0035-03. Bradley JS, Byington CL, Shah SS, Alverson B, Carter ER, Harrison C, Kaplan SL, Mace SE, McCracken GH, Moore MR, et al. The Management of Community-Acquired Pneumonia in Infants and Children Older Than 3 Months of Age: Clinical Practice Guidelines by the Pediatric Infectious Diseases Society and the Infectious Diseases Society of America. Clin Infect Dis. 2011;53(7):e25–e76. doi:https://doi.org/10.1093/cid/cir5314. Gross I, Gordon O, Cohen‐Cymberknoh M, Reiter J, Tsabari R, Gileles‐Hillel A, Erlichman I, Hevroni A, Shoseyov D, Kerem E. Giant lung cysts following necrotizing pneumonia: Resolution with conservative treatment. Pediatr Pulmonol. 2019;54(6):901–906. doi:https://doi.org/10.1002/ppul.243215. Imamoğlu M, Cay A, Koşucu P, Ozdemir O, Cobanoğlu U, Orhan F, Akyol A, Sarihan H. Pneumatoceles in postpneumonic empyema: an algorithmic approach. J Pediatr Surg. 2005;40(7):1111–1117. doi:https://doi.org/10.1016/j.jpedsurg.2005.03.048Authors and affiliations : Sila Y. Kocer 1, Nathan C. Hull MD 2, D. Dean Potter, Jr. MD3, Theresa Madigan MD 4, Jennifer M. Boland MD 5 and Nadir Demirel MD 61Ondokuz Mayis University School of Medicine, Samsun, Turkey2Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA. Email address: [email protected] of Pediatric Surgery, Department of Surgery, Mayo Clinic, Rochester, Minnesota, USA. Email address: [email protected] of Pediatric Infectious Diseases, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, Minnesota, USA. Email address: [email protected] of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota, USA. Email address: [email protected] of Pediatric Pulmonology, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, Minnesota, USA. Email address: [email protected] of interest: The authors declare no conflict of interest.

An Unusual Case of Necrotizing Pneumonia Presenting with Acute Kidney InjuryUgur Berkay Balkanci, MDSchool of Public Health, University of Minnesota, Minneapolis, MNDavid J. Sas, DODivision of Pediatric Nephrology and Hypertension, Department of Pediatrics and Adolescent Medicine, Mayo Clinic, Rochester, MinnesotaNadir Demirel, MDDivision of Pediatric Pulmonology, Department of Pediatrics and Adolescent Medicine, Mayo Clinic, Rochester, MinnesotaCorresponding Author:Nadir Demirel, MDDivision of Pediatric Pulmonology200 First Street SWRochester, MN 55906Tel. No.: 5075380754Fax No.: [email protected] words: postinfectious glomerulonephritis, pneumothorax, complications, complicated pneumoniaFinancial Disclosure: The authors have indicated they have no financial relationships relevant to this article to disclose.Funding: No external funding.Short title: “An unusual case of necrotizing pneumonia”To the Editor:Lower respiratory tract infections are the most common reason for hospitalization in the pediatric age group in the United States. Although pneumonia is prevalent, complicated pneumonia such as empyema, lung abscess and necrotizing pneumonia (NP) is uncommon in children1. The prevalence of complicated pneumococcal pneumonia decreased significantly after the introduction of the thirteen-valent pneumococcal vaccine in 20101. NP in the pediatric population is a severe disease characterized by extensive destruction and liquefaction of the lung tissue resulting in loss of the pulmonary parenchymal architecture, cavitation of the lung, and pleural involvement. Renal complications of complicated pneumonia are rare and mostly reported as atypical hemolytic uremic syndrome (HUS)2. Post-infectious glomerulonephritis (PIGN) is an unexpected complication of bacterial pneumonia3.We report a six-year-old otherwise healthy fully vaccinated girl with a 4-day history of fever, abdominal pain, vomiting, non-bloody diarrhea, and poor oral intake. Parents reported decreased urine output and dark-colored urine on the day of admission. Initial evaluation revealed serum creatinine of 5.01 mg/dL and blood urea nitrogen of 86 mg/dL, elevated acute phase reactants suggesting acute kidney injury (AKI) in the setting of an undiagnosed acute infectious process. The patient was admitted with decreased effective circulatory volume. Urinalysis revealed hematuria with <25% dysmorphic red blood cells (RBCs), proteinuria, pyuria, and RBC casts and granular casts, suggestive of acute glomerulonephritis.She was started on intermittent hemodialysis at day 2 of admission to address uremia, fluid overload, and hyperphosphatemia. A renal biopsy revealed diffuse exudative glomerulonephritis, consistent with infection-related glomerulonephritis. ASO, Anti-DNase B were negative; C3, C4 levels were low. She was treated with pulse IV methylprednisolone 10mg/kg/day for three days. The first 5 days in the hospital, the patient remained afebrile and her lung exam was normal without respiratory symptoms.On day six of admission, she developed acute right-sided chest pain and shortness of breath during hemodialysis. Chest x-ray (CXR) revealed a large right-sided tension pneumothorax, prompting therapeutic chest tube placement. Repeat CXR revealed reexpansion of the right lung and a significant right upper lobe consolidation with an ovoid hyperlucency and an air-fluid level. A chest CT scan confirmed the diagnosis of NP with multiple cavities (Image).Flexible bronchoscopy was performed with bronchoalveolar lavage revealing 42% neutrophils and negative cultures. She was treated with broad spectrum intravenous antibiotics.During admission, she developed hypertension, well-controlled with scheduled enalapril and amlodipine, as well as isradipine as needed. On day 14 of admission, hemodialysis was discontinued as kidney function improved, and chest tube was removed. She was discharged at day 26 of admission on intravenous ceftriaxone and oral metronidazole to complete 30 days of treatment. A repeat chest CT at end of treatment showed complete resolution of NP. Renal functions and blood pressure normalized on follow up.NP is characterized by persistent high fevers and prolonged hospitalizations even with appropriate antibiotic treatment1. Most often, NP affects immunocompetent children with no underlying risk factors4. The pathophysiology of this complication is acute liquefactive necrosis of the lung parenchyma which results in the development of pneumatoceles4. The most common pathogen causing NP is Streptococcus pneumoniae followed by Staphylococcus aureus and Streptococcus pyogenes. Other rarer bacterial and viral pathogens are Mycoplasma pneumonia, Influenza, and Adenovirus1. Identifying the microbiologic pathogen can be challenging and is only made in 50% of cases1. In our case, we did not isolate the causative microorganism. NP typically resolves without residual morbidity, even after a protracted course1,4.Pleural involvement is almost universal in NP, and the course of pleural disease often determines duration and outcome, particularly as it relates to the complication of bronchopleural fistula (BPF)1. BPF is most likely due to the necrotic development of a connection between bronchial space and pleural space4. BPF formation is associated with a significantly longer hospital stay in children with NP4. Yet, most cases heal without surgical intervention4. Tension pneumothorax has been observed as a rare complication of NP1.Renal involvement in complicated pneumonia is rare. Atypical HUS has been reported as a complication of pneumonia, particularly associated with empyema. (most commonly due to invasive Streptococcus pneumoniae)2. In a case series of 37 cases of atypical HUS, 34 patients (92%) had pneumonia with 10 patients (29%) with NP5. Less commonly, pneumonia can be associated with PIGN. PIGN is the most common glomerulonephritis in children worldwide. Pneumonia-associated PIGN is rare. In a case series from the US, PIGN accounted for 0.15% of admissions for pneumonia and 0.39% of admissions for glomerulonephritis6. Pneumonia-associated PIGN is known to be caused by various bacterial pathogens including Streptococcus pneumoniae, Staphylococcus aureus, Mycoplasma pneumoniae, Chlamydia pneumoniae, Nocardia, and Coxiella burnetii3. Different from the usual presentation of the PIGN (in which the time interval between a pharyngeal group A Streptococcal infection and PIGN is 6 to 10 days), pneumonia-associated PIGN is usually concomitant with the pulmonary disease3,6.Our case is unusual in several ways: pneumonia-associated PIGN typically presents with respiratory symptoms first, and acute kidney injury developing during the course of pneumonia3. More surprisingly, the patient developed NP which is characterized by even more severe respiratory symptoms1. Yet, our patient presented without respiratory complaints and pneumonia became apparent only after the development of pneumothorax. We could only identify 2 cases of pneumonia-associated PIGN who presented with renal involvement before pulmonary complaints6,7. Also, previous cases in the literature of pneumonia-associated PIGN report mostly a non-complicated course of pulmonary disease3,6. In a case series of 11 children with pneumonia-associated PIGN, only one case developed a small empyema6. Similarly, the majority of the reported cases of pneumonia-associated PIGN describe a benign course of renal disease3,6. Our patient’s kidney failure progressed rapidly, and she required 2 weeks of intermittent hemodialysis and a three-day course of pulse steroid therapy. At present, systemic corticosteroids are not recommended for patients with complicated pneumonia. A Cochrane review including 17 randomized controlled trials, of which four were conducted on children, found that corticosteroid therapy reduced mortality and morbidity in adults with severe CAP, and morbidity, but not mortality, in adults and children with non-severe CAP1. We speculate that pulse steroid treatment may have modified the course of NP in our patient.This case suggests an atypical presentation of NP with predominant renal complications is possible. Pediatricians should be aware of renal complications of respiratory diseases. Systemic steroids should be considered in the treatment of NP.References:1. de Benedictis FM, Kerem E, Chang AB, Colin AA, Zar HJ, Bush A. Complicated pneumonia in children. Lancet 2020;396:786-798.2. Spinale JM, Ruebner RL, Kaplan BS, Copelovitch L. Update on Streptococcus pneumoniae associated hemolytic uremic syndrome. Curr Opin Pediatr 2013;25:203-208.3. Carceller Lechón F, de la Torre Espí M, Porto Abal R, Écija Peiró JL. Acute glomerulonephritis associated with pneumonia: a review of three cases. Pediatr Nephrol 2010;25:161-164.4. Sawicki GS, Lu FL, Valim C, Cleveland RH, Colin AA. Necrotising pneumonia is an increasingly detected complication of pneumonia in children. Eur Respir J 2008;31:1285-1291.5. Banerjee R, Hersh AL, Newland J, Beekmann SE, Polgreen PM, Bender J, Shaw J, Copelovitch L, Kaplan BS, Shah SS. Streptococcus pneumoniae-associated Hemolytic Uremic Syndrome Among Children in North America. Pediatr Infect Dis J 2011;30:736-739.6. Srivastava T, Warady BA, Alon US. Pneumonia-associated acute glomerulonephritis. Clin Nephrol 2002;57:175-182.7. Schachter J, Pomeranz A, Berger I, Wolach B. Acute glomerulonephritis secondary to lobar pneumonia. Int J Pediatr Nephrol 1987;8:211-214.