Purpose or Case Report: An afebrile 23-month-old boy with history of VSD, PFO and GERD who presented with one day of acute left sided abdominal pain, nausea and vomiting. Following a benign clinical work-up only significant for mild leukocytosis and transient small bowel to small bowel intussusception on abdominal US, he was discharged home. He re-presented a few days later with worsening abdominal pain and low grade fever and was found to have increased leukocytosis and elevated CRP. KUB demonstrated a new left lower lobe opacity. Non-contrast CT abdomen showed a well circumscribed ovoid hyperdense soft tissue mass in the inferomedial left lower lobe, a small left pleural effusion, and adjacent passive atelectasis. On chest MRI , the left lower lobe soft tissue mass demonstrated T1 isointense to hyperintense and STIR hypointense signal with mild restricted diffusion and no enhancement on post-contrast images. MRA of the chest was negative for any feeding vessel extending to the lesion. Video-assisted thoracotomy surgery revealed a torsed, bluish left lower lobe mass adherent to the mediastinum with thrombosed vessels at its pedicle. Pathology results confirmed the suspected diagnosis of an infarcted and hemorrhagic extralobar pulmonary sequestration.

Pulmonary sequestration is a rare congenital malformation of the foregut, where a nonfunctional supranumary segment of the lung lacking a normal connection to the tracheobronchial tree develops below the normal lung bud. The sequestration can be intralobar or extralobar, depending on the pleural investment, has arterial supply from systemic circulation, and venous drainage via pulmonary and/or systemic venous drainage. Torsed pulmonary sequestrations are extremely rare and occur when the sequestration twists around the axis of its vascular pedicle resulting in ischemia or infarction of the non-functional lung tissue. In the case of a full torsion, the vascular supply may not be visualized at imaging. Thus it is important to consider pulmonary sequestration as a differential diagnosis in a pediatric patient presenting with lower chest or abdominal pain with a circumscribed lower lobe pulmonary mass, even without characteristic feeding vessels on MRI/MRA.
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