Conscientious assessment of abnormal scans coupled with clinical assessment and biochemical correlation is essential to avert needless surgical intervention or ensuing ablation with high-dose radioiodine. False-positive I-131 uptake in WBS comprising the chest region has been reported in the literature. The aetiology encompasses acute respiratory infection, pulmonary tuberculosis, pulmonary aspergilloma, rheumatoid lung disease and bronchiectasis .
Pulmonary sequestration is an uncommon congenital anomaly of the lower respiratory tract which comprises a mass of lung tissue that is non-functioning . The incidence of pulmonary sequestration is 1 in 10,000 to 35,000 live births and represents 1 to 6% of the congenital abnormalities involving the lower airway [2, 3]. In general, pulmonary sequestration can be classified into two forms. Intrapulmonary sequestration which is enclosed inside the visceral pleura of the adjoining lung accounts for 75% of the cases while extrapulmonary sequestration, which is situated externally with its own visceral pleura contributes the remaining 25% . Interestingly, almost two-thirds of intrapulmonary sequestration are found in the posterobasal segment of the left lower lobe  as demonstrated in this case.
The pathophysiology of pulmonary sequestration is not completely understood. The universally approved understanding is that it is derived during development from an accessory lung bud inferior to the normal lung buds [2, 3]. At the time of embryogenesis, the accessory lung bud acquires a separate vascular supply, independent from the normal developing tracheobronchial tree . The airways of the lesion often reveal mucus accumulation, regions of inflammation, microcystic changes and distortion of lung parenchyma, while pathological examination demonstrates enlarged and thickened airspaces in the abnormal parenchyma .
The majority of patients are asymptomatic, and the disease is often diagnosed during routine medical examination or in recurrent bacterial lung infection affecting the lower lobe . Symptoms are often non-specific consisting of chest pain, breathlessness, wheezing, fever, cough and recurrent infections , with infection being noted as the most common complication . Other complications include creation of left to right shunt and haemorrhage, which can be fatal .
Imaging of pulmonary sequestration includes (i) arteriogram, which is vital in documenting systemic blood supply, (ii) chest X-ray, which usually shows homogenous dense mass in the thoracic cavity, (iii) ultrasound, which shows echogenic mass that is well defined or irregular, (iv) computed tomography (with accuracy of diagnosis of approximately 90%), which shows solid homogenous or heterogenous mass and reveals anatomic position with vascular anatomy, and (v) magnetic resonance imaging, which demonstrates lung mass, systemic blood supply along with its venous drainage [2, 5]. Management of lung sequestration in the asymptomatic patient is subject to controversy. Most authors advocate surgical resection of the lesions owing to the propensity for recurrent infection and possibility of haemorrhage .
Up to the present, only two cases of pulmonary sequestration causing false-positive findings in I-131 whole-body scan have been reported. The first case was reported by Jimenez-Bonilla et al.  in 2013 which showed I-131 uptake in a lesion at the right posterior costodiaphragmatic recess followed by Spinapolice et al.  in the ensuing year which reported a case of I-131 uptake of a nodular lesion in the upper mediastinum in between the aortic arc and pulmonary artery. The mechanism of I-131 uptake in pulmonary sequestration is not known. Examination of the surgical specimen from the case report by Spinapolice et al.  demonstrates a huge haemorrhagic infiltrate which might be responsible for I-131 fixation in the pulmonary sequestration.
In cases of discordant findings of low or undetectable serum Tg (with negative anti-TgAb) but positive I-131 WBS, single-photon emission computed tomography/computed tomography (SPECT/CT) is strongly advocated whenever available. Study by Zilioli et al.  has shown that SPECT/CT has an additional value over planar whole-body scan in augmenting accuracy of diagnosis and lowering pitfalls and alters patient management by providing anatomical correlation and localization of radioiodine uptake.