pulmonary alveolar microlithiasis ( pam ) is a rare chronic disease characterised by calcifications within the alveoli ( calcospherites ) and a paucity of symptoms in contrast to the imaging findings . patients are usually symptom - free until middle age when chronic respiratory failure starts to develop . the diagnosis of pam is incidental in the early age as in this present case . a 24-year - old malay male patient was referred to the respiratory clinic because of an abnormal pre - employment chest radiograph . he had been smoking about 10 cigarettes a day since he was 21 years of age . he stopped smoking 10 months ago after he noticed he had being having reduced effort tolerance for the past three years . he was an office worker and did not have a history of exposure to organic or inorganic dusts . his oxygen saturation on room air at rest was 94% and dropped to 92% after climbing up four flights of stairs . spirometry testing revealed a restrictive pattern of lung disease with a forced expiratory volume in 1 second ( fev1 ) and a forced vital capacity ( fvc ) of 2.7 l ( 69% of predicted ) and 3.2 l ( 68% of predicted ) , respectively . g / l ) , serum parathyroid hormone ( 2.9 pmol / l [ normal , 1.1 - 7.3 ] ) and calcium ( 2.34 24-hour urine calcium was also normal 6.9 mmol with a 24-hour urine volume of 2.8 l. his chest radiograph ( fig . 1a ) revealed dense micronodular opacities distributed symmetrically and predominantly in the middle to lower zones of both lungs giving the classical " sandstorm " appearance . the cardiac borders were obscured by the sand - like opacities . a high - resolution 1b ) showed widespread tiny microcalcifications throughout the lungs with a preponderance of microliths in the lower lobes . subpleural cystic changes were also seen in both lower lobes giving rise to the ' black pleura sign ' ( fig . both the bronchial system ( including the small bronchioles ) and the size of the pulmonary vessels were normal . as this was diffuse parenchymal lung disease , videoassisted thoracic surgical ( vats ) lung biopsy was planned but the procedure was converted into a mini - thoracotomy because there was difficulty in manoeuvering the endostapler . there was a moderate pneumothorax postmini - thoracotomy from which the patient fully recovered after 5 days in the ward . the lung biopsy specimen revealed features consistent with pam , with numerous calcospherites within the alveolar spaces ( fig . the intervening alveolar septae were congested and showed mild fibrosis with infiltrates of mainly lymphoplasmacytic cells . pulmonary alveolar microlithiasis is characterised by the presence of numerous tiny calculi ( calcospherites ) within the alveolar spaces , and occurs worldwide with most of the cases coming from europe ( 42.7% ) and asia ( 40.6% ) ( 3 ) . the peak incidence in japan occurs between the ages of four to nine years , while in the west , the majority of reported cases have been in patients between the ages of 30 to 50 years . there is no gender predilection for this disease . in our case , this young malay male was less than 30 years old . hypothetical mechanisms that have been proposed include an inborn error of metabolism , an unusual response to an unspecified pulmonary insult , an immune reaction to various irritants , and an acquired abnormality of calcium or phosphorus metabolism . recently , there have been reports of mutation in type iib sodium - phosphate cotransporter gene ( scl34a2 gene ) in the disease pathogenesis ( 5 ) . plain chest radiographs typically show bilateral areas of micronodular calcifications producing a " sandstorm " appearance that predominates in the middle and lower lung areas as in our patient . the lung bases appear to have increased density due to the greater thickness of the lung tissue there , as well as increased surface densities . this distribution of calcified nodules may be due to the relatively richer blood supply to this area ( 6 ) . high - resolution computed tomography of the thorax shows alveolar calcification that is a mixture of calcified micronodules in a ground glass pattern or consolidation accentuated along the pleural margins and fissures adjacent to the interlobular septa giving rise to polygonous structures and bronchovascular bundles , explaining the coarsely linear nodulations , reticulations and septal lines seen on the hrct of this patient . the predominance of calcification in the medial rather than the lateral portions of the lung as described by hoshino et al . some authors consider the interlobular septa of calcium density due to deposition of calcospherites within the peripheral lobular parenchyma as pathognomonic of pam on the hrct scan ( 4 ) . calcospherites measuring less than 1 mm produce a ground - glass appearance , and with appropriate windowing , such as a bone window , can often be discerned as discrete calcifications ( 8) . it has been postulated by hoshino et al . that the black pleural line on hrct is caused not by subpleural cysts but by a fat - dense layer between the ribs and the calcified lung parenchyma . however , a review of the ct and pathologic findings in 10 patients with pam revealed that the sub - pleural cysts on ct were histologically dilated alveolar ducts ( 9 ) . magnetic resonance imaging ( mri ) in their patients with pam showed diffusely increased signal intensity on t1-weighting at the lower lung zones ( 7 ) . mri was not performed in our patient as an hrct was considered sufficient for diagnosing this patient . this patient 's hrct had features characteristic of pam , which are calcified nodules , calcifications along the interlobular septa and pleura , ground - glass opacities , consolidation , and subpleural cysts . these hrct features are better demonstrated with 0.75 mm slice thicknesses than with 10 mm thicknesses , which were used prior to 2005 ( 9 ) . chest radiograph and ct scan findings are characteristic , and along with the clinical dissociation ( as well as the blood results ) , are sufficient for diagnosis of the disease , even if microscopic evidence of calcospherites in the alveoli is obtained , as in this patient ( 3 ) . lung biopsy for diffuse lung disease such as this is best approached by vats or open thoracotomy as ct guided lung biopsy is associated with a high risk of complications such as pneumothorax and bronchopleural fistula . bronchoalveolar lavage has also been used to recover calcospherites which are seen as rounded concentrically laminated masses histopathologically . some patients are followed up for more than 30 years without evidence of significant deterioration ( 10 ) . end - stage lung disease was reported to occur more frequently among cigarette smoking pam patients . the florid appearance of pam on chest radiograph and hrct in this patient may be attributed to the smoking history . systemic steroids and bronchoalveolar lavage have not been proven to be effective ( 11 ) . pulmonary alveolar microlithiasis is a disease with characteristic radiological and pathological features , and it is asymptomatic till it progresses to restrictive lung disease . as it is uncommon , the radiologist needs to keep this disease in mind if conditions that produce a similar appearance such as occupational lung disease have been excluded .
pulmonary alveolar microlithiasis ( pam ) is a rare chronic disease with paucity of symptoms in contrast to the imaging findings . 
 we present a case of a 24-year - old malay man having an incidental abnormal pre - employment chest radiograph of dense micronodular opacities giving the classical " sandstorm " appearance . 
 high - resolution computed tomography of the lungs showed microcalcifications with subpleural cystic changes . 
 open lung biopsy showed calcospherites within the alveolar spaces . 
 the radiological and histopathological findings were characteristic of pam .