Objectives Humans receiving tissue-engineered tracheal grafts have experienced poor outcomes ultimately resulting in death or the need for graft explantation. We assessed the performance of the synthetic scaffolds used in humans with an ovine model of orthotopic tracheal replacement, applying standard postsurgical surveillance and interventions to define the factors that contributed to the complications seen at the bedside. Study Design Large animal model. Setting Pediatric academic research institute. Subjects and Methods Human scaffolds were manufactured with an electrospun blend of polyethylene terephthalate and polyurethane reinforced with polycarbonate rings. They were seeded with autologous bone marrow–derived mononuclear cells and implanted in sheep. Animals were evaluated with routine bronchoscopy and fluoroscopy. Endoscopic dilation and stenting were performed to manage graft stenosis for up to a 4-month time point. Grafts and adjacent native airway were sectioned and evaluated with histology and immunohistochemistry. Results All animals had signs of graft stenosis. Three of 5 animals (60%) designated for long-term surveillance survived until the 4-month time point. Graft dilation and stent placement resolved respiratory symptoms and prolonged survival. Necropsy demonstrated evidence of infection and graft encapsulation. Granulation tissue with signs of neovascularization was seen at the anastomoses, but epithelialization was never observed. Acute and chronic inflammation of the native airway epithelium was observed at all time points. Architectural changes of the scaffold included posterior wall infolding and scaffold delamination. Conclusions In our ovine model, clinically applied synthetic tissue-engineered tracheas demonstrated infectious, inflammatory, and mechanical failures with a lack of epithelialization and neovascularization.

Clinical Vignette introduCtionThe morphologic recognition of organisms remains an important component of the diagnostic work up of a specimen in general pathology practice. An accurate interpretation requires familiarity with an organism's typical morphology as well as morphologic variations, including artificial changes. This case report illustrates the morphologic transformation of antibiotic altered Pseudomonas aeruginosa in the cerebrospinal fluid of a young boy. CliniCal historyOur patient is a 17-year-old boy with a history of hydrocephalus and placement of a ventriculoperitoneal shunt who presented with fever. Recent medical history included bacteremia, with blood cultures positive for Propionibacterium acnes. On hospital day 1, the patient was started on empiric broad-spectrum antibiotics: vancomycin (20 mg/kg every 6 h); cefepime (intravenous, 50 mg/kg every 8 h); Flagyl (intravenous, 10 mg/kg every 8 h); and amikacin (intravenous, 20 mg/kg daily). Cultures from cerebrospinal fluid (CSF) grew pansensitive P. aeruginosa. Subsequent peritoneal fluid and distal catheter cultures on day 2 postadmission grew P. aeruginosa, and subsequently, the shunt was removed on day 3 postadmission (shunt hardware cultures also grew P. aeruginosa). Vancomycin and amikacin were subsequently discontinued (3 days of therapy each). On day 7 postadmission, a repeat CSF fluid analysis showed an elevated white blood cell (WBC) count of 674, and gentamicin (intravenous, 2.5 mg/kg every 8 h) was added for secondary Gram-negative coverage. Flagyl was discontinued on postadmission day 9 after anaerobic cultures remained negative (9 days of therapy), and gentamicin was discontinued on postadmission day 10 given recent negative routine CSF cultures (4 days of therapy). Unfortunately, a culture from the patient's external ventricular drain on postadmission day 11 was again positive for P. aeruginosa, and ciprofloxacin (intravenous, 10 mg/kg) was added on postadmission day 12. Subsequent cultures were negative, Certain bacteria and antibiotic combinations can result in unusual morphologic transformations such as the creation of septate filamentous bacterial rods, where division is preserved, but separation is inhibited. This is often seen when subinhibitory concentrations of antibiotics are administered. Herein, we describe this phenomenon in the case of a teenage boy with an infected ventriculoperitoneal shunt, whose culture-proven Pseudomonas aeruginosa took on a filamentous appearance following antibiotic treatment. This transformation is important to recognize, so it is not misconstrued as fungal hyphae, committing the patient to unnecessary treatment.