British Journal of Radiology (2004) 77, 974-976
© 2004 British Institute of Radiology
doi: 10.1259/bjr/96331922
Pulmonary alveolar microlithiasis presenting with crazy-paving pattern on high resolution CT
E L Gasparetto, MD
1
P Tazoniero, MD
1
D L Escuissato, MD
1
E Marchiori, MD
1
R L Frare e Silva, MD
2 and
D Sakamoto, MD
3
Departments of 1 Diagnostic Radiology, 2 Internal Medicine and 3 Pathology, University of Paraná School of Medicine, Curitiba, PR, Brazil
Correspondence: Emerson L Gasparetto, Serviço de Radiologia Médica, Hospital de Clínicas da UFPR, Av General Carneiro 181, CEP: 80060900, Curitiba, Paraná, Brazil
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Abstract
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Pulmonary alveolar microlithiasis (PAM) is an uncommon chronic disease characterized by calcifications within the alveoli and a paucity of symptoms in contrast to the imaging findings. We present a 59-year-old woman with a 4-year history of shortness of breath on exertion. Lung auscultation revealed random wheezes and fine and coarse crackles. Pulmonary function tests showed a restrictive pattern. The chest radiograph demonstrated a bilateral symmetric micronodular pattern. High resolution CT scan revealed diffuse ground-glass attenuation with superimposed septal thickening ("crazy-paving" pattern). The patient underwent a lung biopsy, which confirmed the diagnosis of PAM. Our case demonstrates that PAM needs to be considerate in the differential diagnosis of lung lesions that present with crazy-paving pattern on the high resolution CT.
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Introduction
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Pulmonary alveolar microlithiasis (PAM) is a rare chronic disease characterized by widespread calcifications within the alveoli and paucity of symptoms [1–5]. It occurs sporadically and it is regarded as an autossomal recessive lung disease. The pathogenesis of PAM has yet to be elucidated [6–8].
The authors present a case of PAM and stress the high-resolution CT findings of this rare entity, emphasising the "crazy-paving" pattern observed in this case.
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Case report
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A 59-year-old female non-smoker presented with a 4-year history of shortness of breath on exertion. In the last 5 months the dyspnoea progressed and was associated with a productive cough. At physical examination, mucosal cyanosis was observed and auscultation of the lungs has revealed random wheezes and coarse crackles. Cardiac auscultation revealed a hyperphonetic S1 and S2 and fixed splitting of S2. Discrete oedema of the legs was also observed. A full blood count revealed an elevated erythrocyte count of 6.58 x 106 µl–1 and globular volume (57 g%). Arterial blood gas analysis values in room air were: pH: 7.4, PaO2: 52 mmHg, PaCO2: 27 mmHg, HCO3: 17 mmol l–1 and O2 saturation 87.1%. Pulmonary function tests revealed typical features of a restrictive defect with a reduced total lung capacity of 58% and vital capacity of 48%, and a forced expiratory volume in 1 s/forced vital capacity (FEV1/FVC):108. Echocardiography showed severe pulmonary hypertension, 84 mmHg, a dilated right heart and moderate tricuspid regurgitation.
The chest plain films revealed a diffuse symmetric dense bilateral micronodular ("sand-storm") pattern. Along the lateral right base of chest wall, a dense subpleural layer and a black pleural line were noted (Figure 1
). A high resolution CT scan (Somaton ART; Siemens, Germany) was obtained at maximal inspiration at 10 mm intervals in the supine position. All scans were photographed with window/level settings of 770/10, 1730/–810 and 1910/–500 Hounsfield Units. The examination showed diffuse symmetric lung abnormalities characterized by ground-glass attenuation and septal thickening with calcified nodules, resulting in a crazy-paving pattern. Subpleural calcification was also seen (Figure 2).
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Figure 1. Chest radiograph shows a diffuse symmetric lung lesion with dense micronodular aspect ("sand storm").
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Figure 2. (a) High resolution CT scan reveals diffuse ground-glass attenuation and septal thickening with calcified nodules, defining the "crazy-paving" pattern (window/level 1730/–810 HU). (b) The septal thickening is more clearly visualized with this window/level (770/10 HU). Calcifications of subpleural aspect are also seen.
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The patient underwent a transbronchial lung biopsy. Histology revealed round, concentrically laminated microliths in the alveoli, which were periodic acid-Schiff (PAS) positive in keeping with the diagnosis of PAM.
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Discussion
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The main characteristic of PAM is widespread laminated calcipherites in the alveolar spaces in the absence of any known disorder of calcium metabolism [5]. Patients may remain asymptomatic for many years and do usually become symptomatic between the third and fourth decades [1, 4]. The clinical presentation usually demonstrates a lung disorder with restrictive pattern [1, 3–5], as seen in our patient. Pneumothorax can be observed in the early course of the disease [6]. Adult patients commonly show progressive deterioration of the pulmonary function and death usually occurs in mid-life because of respiratory failure associated with cor pulmonale [6].
Plain chest radiographs usually reveal diffuse, scattered, bilateral areas of micronodular calcifications ("sand storm"), that predominate in the middle and lower lung areas [1–5]. The lung bases appear of increased density owing to the greater thickness of lung tissue in these areas, as well as the increased surface densities [2]. The distribution of the calcified nodules can also be explained by the relative higher blood supply to this area [4]. The heart borders and the diaphragm are usually obliterated. Other typical findings include small apical bullae [3] and a black pleural line, which is demonstrated as an area of increased translucence between the lung parenchyma and the ribs [2, 3]. The chest radiographs of our patient showed a diffuse symmetric lung lesion with dense micronodular aspect, corroborating the pattern previously described in the literature.
The CT scan usually reveals diffuse ground-glass opacities throughout both lungs, associated with confluent and diffuse calcified nodules. This imaging technique confirms the predominance of symmetric abnormalities at the middle and lower zones. Calcifications along the bronchovascular bundles and at the central region of the bronchovascular tree can also be seen. A predominance of calcifications in the medial areas when compared with the lateral portions of the lungs is also evidenced in the CT scan [1, 2]. High resolution CT scans may reveal small cysts in the subpleural lung parenchyma, pleural calcification and small calcispherites within the thickened pleura [2, 3]. Some of these findings were observed in our case, whose CT demonstrated diffuse ground-glass attenuation and septal thickening with calcified nodules, as well as subpleural calcification.
Since Murch and Carr [9] described the crazy-paving pattern as characteristic of pulmonary alveolar proteinosis, several diseases have demonstrated this finding, making the differential diagnosis by high resolution CT sometimes difficult [10, 11]. This pattern has not previously been described in patients with PAM. In our patient, the crazy-paving pattern assumed unique characteristics, since at mediastinal windows the interlobular septa were of calcium density due to deposition of calcipheriths within the peripheral lobular parenchyma, adjacent to the septa. Therefore, we suggest that the crazy-paving pattern with calcifications along the interlobular septa may also be considered diagnostic of PAM.
High resolution CT scan remains the imaging technique of choice to diagnose PAM. Although not previously reported, our case demonstrates that PAM needs to be considered in the differential diagnosis of lung lesions that present with a crazy-paving pattern on high resolution CT scan.
Received for publication November 11, 2003.
Revision received April 26, 2004.
Accepted for publication May 19, 2004.
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References
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Abstract
Introduction
