lipoid pneumonia ( lp ) is a rare inflammatory disease of the lung parenchyma caused by accumulation of fatty oily material in the alveoli . exogenous lipoid results from aspiration or inhalation of mineral , vegetable , or animal oil into the peripheral lung . children can aspirate large amounts of different oily materials , mineral oil being the most frequently encountered substance , and this happens especially when certain risk factors are present . the aspiration of fatty material elicits a pulmonary inflammatory reaction that produces non - specific clinical and radiologic findings , often similar to those of bacterial pneumonia and tuberculosis , complicating or delaying the diagnosis . thus , it is imperative to identify correctly this entity when there is a high degree of suspicion , through a thorough and focused noting of patient 's medical history and an accurate recognition of its radiologic manifestations . we present a case of acute lp in a 5-month - old infant due to accidental mineral oil aspiration , confirmed by analysis of bronchoalveolar lavage ( bal ) and focus on the radiologic findings showing evolution of parenchymal lesions over a follow - up period of 7 years . this was a case report of a 5-month - old male infant who was admitted as an emergency case to a secondary care hospital with acute onset of high - grade fever and respiratory distress . the chest x - ray showed bilateral extensive consolidation involving mainly the lower lobes of the lungs . he was placed on broad spectrum antibiotics and bronchodilatory inhalers , in response to which he showed no clinical improvement over a period of 2 days . therefore , and in view of his deteriorating clinical status , he was urgently transferred to our hospital for further management . upon arrival , the infant was in respiratory distress requiring 4 l / min of oxygen to keep his oxygen saturation above 90% . further examination of the infant revealed dysmorphic features such as low set ears , generalized muscular hypotony , and delayed psychomotor development . additional questions on patient history identified that at the age of 5-months the child had accidentally ingested paraffin oil administered by his 3-year - old brother . computed tomography ( ct ) scan [ figure 1a ] revealed extensive bilateral consolidations in the lower lobes . the bal aspirate was opalescent with a supernatant halo of fat and showed an increased number of macrophages . bal was sent for microbiological studies including gram staining , ziehl - neelsen staining , and bacterial and fungal cultures . the cytologic study showed numerous foamy macrophages with intracytoplasmic and extracellular droplets of fat with a positive histochemical confirmation of acute lp with oil red o stain . ( oil red o is a fat - soluble dye used for staining of lipids and triglycerides . ) total lavage was not performed as it was considered too risky in view of the critical status of the patient and the signs of hypoxia he demonstrated during the procedure . 5-month - old male infant aspirated large amounts of paraffin oil causing respiratory distress diagnosed later as due to lipoid pneumonia ( a ) chest computed tomography ( ct ) performed 1.5 month post - paraffin oil aspiration shows diffuse extensive airspace consolidations ( arrows ) in both lower lobes . ( b ) high - resolution chest ct taken 7 months after the incident shows persistent imaging findings ( arrows ) with minimal improvement . a corticosteroid therapy regimen was introduced which led to an improvement of his general condition . the infant remained in our hospital for a total of 5 months showing gradual clinical improvement . before discharge an additional bronchoscopy and bal was performed that showed a clear aspirate with no supernatant fat and fewer lipid - laden macrophages . further , an additional ct scan was performed which showed persistent findings with minimal improvement [ figure 1b ] . he underwent spirometry , which revealed a forced vital capacity ( fvc ) equal to 85% of predicted value , a forced expiratory volume in 1 s ( fev1 ) of 79% of predicted value . fev1/fvc ratio was 81% , which was within the normal range ( approximate range : 75 - 80% ) for healthy adults . the patient could not undergo further pulmonary function testing ( lung volume , diffusing capacity of lung for carbon monoxide ) . bal revealed far fewer lipid - laden macrophages , while the ct scan showed resolution of the consolidations , but evidence of residual interstitial findings [ figure 2 ] . follow - up high - resolution chest computed tomography taken 7-years after the episode of aspiration , shows bilateral thickening of the interlobular septa ( open arrow ) , streaky peripheral infiltrates ( arrows ) and areas of hyperinflation . lp is an uncommon pulmonary disorder that results from the accumulation of lipids in the alveoli . on the basis of the source of the lipid the exogenous type is due to aspiration of animal fat , vegetable or mineral oil and can be acute or chronic in presentation . acute exogenous lp is a type of pneumonitis associated with an incident of aspiration of a large amount of an oil - based product . most cases of exogenous lp result from aspiration of mineral oil , which is usually used for the treatment of refractory constipation . in early childhood , the factors that increase the risk of aspiration , in both the acute and chronic form , are commonly associated with underlying conditions , such as disruption of the normal physiologic function of the airway and the upper gastrointestinal tract , congenital disorders of the structure and function of the foregut , and impairment of neurologic or neuromuscular control of the process of breathing and/or swallowing . additional predisposing factors to lp in children are gastroesophageal reflux and forced ingestion of oily medication as practiced in a number of geographic areas . our patient showed features of developmental delay along with generalized muscular hypotony , which was hypothesized to have contributed to the aspiration of a large amount of material . acute exogenous lp in children , typically manifests clinically as an acute aspiration condition , which evolves into respiratory failure and , occasionally , death . in the report published by zanetti et al . , 17 children with lp having non - specific clinical presentation , showed air space consolidation on chest radiographs , which suggested bacterial pneumonia . the children showed no improvement with antibiotic therapy and were later investigated with high - resolution ct and bal . only at this stage the time period between the initial radiographs and diagnosis varied from 30 days to 45 days . such a delay was also observed in our case , partially attributed to the initial reluctance of the parents to mention the incident of accidental aspiration , afraid of being accused of lack of proper care of the baby . acute exogenous lp manifests radiologically within 30 min of the episode of aspiration or inhalation . pulmonary opacities can be seen in most patients within 24 h. chest x - ray shows parenchymal abnormalities that include areas of ground - glass opacity or consolidation , bilateral and segmental or lobar in distribution and predominantly involving the middle and lower lobes , similar to those seen in general aspiration pneumonia . high - resolution computed tomography is the imaging technique of choice for investigating lp and , in children , it must be performed with the lowest possible radiation . the principal ct imaging findings include alveolar consolidations , ground - glass opacities , nodular lesions , interlobular septal thickening , and intralobular interstitial thickening . the crazy - paving pattern , consistent with well - defined areas of ground - glass attenuation with superimposed septal thickening , has also been described as a characteristic feature of lp . in addition , exogenous lp may be diagnosed promptly when areas of fat attenuation are identified within a pulmonary air - space consolidation . pure mineral oil has a ct attenuation value of -132 hu and negative density values ( between -30 and -150 hu ) within the consolidation area . these findings , although non - specific , can suggest the diagnosis of lp . however , in some patients with lp , as in the present case , fat attenuation is not evident on ct images because the fat attenuation values are averaged with the surrounding inflammatory exudates so that the fat component becomes less conspicuous or obscure . according to most studies on pediatric patients , the radiologic manifestations of acute exogenous lp typically improve or resolve over time . sias et al . , evaluated 28 children with lp for 24 months and demonstrated normalization of ct scans in 18 of them right after treatment . in two patients scanned 12 months after treatment , a cystic lesion in the right lung and a discrete area of segmented atelectasia treatment abandonment occurred in 6 cases and no further ct follow - up was reported for the remaining children . sias et al . , also demonstrated the potential role of multiple bals in the treatment of lp , in a prospective study of 10 children with lp . in these cases , lp was secondary to mineral oil aspiration , and the delay between aspiration and treatment was 1 - 60 days . over a follow - up period of 6 months , complete radiologic resolution was demonstrated in 3 out of 6 patients who had a short interval between intake of mineral oil ( 1 - 4 days ) and treatment . in the remaining three cases , all four children with a longer time interval between aspiration of mineral oil and treatment had residual areas of consolidations on ct scans taken at 6-months , but no further follow - up was reported . in our case , the follow - up ct scan that was performed 7 years after the aspiration demonstrated architectural distortion associated with thickening of the interlobular septa . mineral oil ( a mixture of inert , long - chain , saturated hydrocarbons obtained from petroleum ) is emulsified and phagocytosed by alveolar macrophages , which , filled with oil , reach the interlobular septum through the lymphatic channels . subsequently , with the permanence of the oil , there is development of chronic interstitial inflammation , which can evolve into pulmonary fibrosis and decreased lung volume . in our case , there was no evidence of end - stage lung lesions and functional respiratory tests were normal . the imaging findings can be attributed to the large amount of aspirated oil , the delay in the correct diagnosis and the fact that the patient did not undergo any therapeutic bal , which has been shown to facilitate the removal of lipid - laden macrophages implicated in development of alveolar and interstitial fibrosis . to the best of our knowledge , this is the longest follow - up study of a pediatric patient with acute lp showing imaging features on ct and the only case reported where a single episode of fat aspiration that is associated with residual interstitial changes in the follow - up ct scan . we have described a case of acute exogenous lp induced by accidental aspiration of mineral oil for which the early imaging findings were consistent with published reports . long - term follow - up , however , revealed partial resolution with persistent interstitial lesions seen on ct scan . a finding that has not been reported in the pediatric population and merits consideration when interpreting imaging examinations of patients with a history of acute lp .