Diseases by aspergillus species mostly affect immunocompromised patients with a broad clinical spectrum that comprises a variety of manifestations even within the lungs. Local pulmonary disease can present as aspergilloma, representing mycelial ball growing in damaged lung areas such as cavities . In semi-invasive disease aspergillomas occur concurrently to progressive fibrosis with minor invasion taking place. Distinct sub-entities have been suggested but are summarized by the term “chronic pulmonary aspergillosis” (CPA)  with around 25% of patients with CPA also having an aspergilloma .
Chronic pulmonary aspergillosis (CPA) affects an estimated 3 million people worldwide . Noteworthy, WHO reports that approximately one third of patients diagnosed with CPA was previously treated for pulmonary tuberculosis (PTB) . Initial clinical presentation of CPA and PTB are often alike. In resource-limited facilities testing for immunoglobulin G (IgG) antibodies against A. fumigatus may often not be available, and thus CPA may often be undiagnosed or misdiagnosed as “smear-negative PTB” and/or “relapse” of TB in endemic settings . Post-TB lung disease (PTLD) is responsible for a notable number of chronic lung diseases worldwide  and its wide-ranging consequences are yet to be understood fully to improve TB treatment outcomes .
Lung ultrasound (LUS) has become an established diagnostic imaging modality for pulmonary conditions in recent years. LUS became a standard tool in emergency medicine for timely diagnosis of pneumothorax  as well as ARDS  and has proven useful as a radiation-free imaging modality with high test accuracy for diagnosis of pneumonia in childhood . Lung ultrasound was even found suitable to differentiate bacterial from viral etiology of community-acquired pneumonia in children .
Reports on the visualization of pulmonary aspergilloma by ultrasound are limited. A clinical report from 2012 describes color Doppler sonography (CDS) of pulmonary aspergillosis in infants with chronic granulomatous disease with detection of systemic arterial feeders to the pleural-based lesions and sonographic findings of aspergillosis reported as “crescent” or “halo” sign, which, interestingly, were not visible on CT . A publication on endobronchial ultrasound from 2016 reports a “central annular image in an ill-defined hypoechoic paraoesophageal lesion” as possibly sonographic characteristic of pulmonary aspergillosis . A similar sonographic characteristic described as the “fluid rim sign” was reported in a case report of musculoskeletal aspergillosis . For hepatosplenic mycotic abscesses the “wheel within wheel” appearance is described as a specific finding on ultrasound .
Using a phased array probe on the left upper zone we obtained transthoracic ultrasound images of a comparable composition with a central roundish structure and a fine anechoic rim (Fig. 1a–b), adding to the hypothesis that this might be a characteristic finding of pulmonary aspergillosis. Visualization of the aspergilloma by lung ultrasound was only possible as the cavity reached the pleura and the mycelial ball almost filled the cavity leaving very little air-filled space within the cavity to interfere with ultrasound. In contrary, the other, even larger cavity in the right upper zone was not clearly discernable on lung ultrasound. Fibrotic margins of this cavity, which were immediately adjacent to the pleura, were detectable as noteworthy pleural irregularities, yet, this massive air-filled space (Fig. 2) could not be comprehensively visualized on ultrasound to adequately detect the lesion as cavity.
Tuberculous cavities on ultrasound have been well described by Agostinis et al. as presenting as roundish anechoic or hypoechoic areas within solid consolidations that have thick and irregular walls and posterior enhancement . Detection rates of cavities on LUS are however low [16, 17], most likely due to air-filled lung between cavity and pleura which impedes visualization of underlying findings. The “crescent” sign has not been described for tuberculous cavities and may therefore be a sonographic feature for differentiating mycotic from tuberculous cavities.
Ultrasound at the point-of-care has developed into a relatively cheap, portable and radiation-free diagnostic tool to augment physical examination, especially where resources are scarce . The value of LUS is being studied for pulmonary TB as low- and middle-income countries often bear a high burden of tuberculosis (TB) and access to standard imaging may be limited [15, 18,19,20]. LUS detects features of pulmonary TB including cavitary or miliary presentation; however, the full discriminatory power of LUS to differentiate PTB from other pulmonary conditions remains to be established. The potential of LUS is an expanding area of research and it might also be worth to further investigate possible distinctive US patterns for different etiologies of pulmonary diseases including detection of pulmonary aspergilloma. However, lung ultrasound does never allow to rule out focal lung pathology because if there is normal lung in between pleura and pathology a characteristic image will not be obtained; for focal pulmonary pathology lung ultrasound may therefore be relevant as a “rule in test” but not as a “rule out test”.
More studies with an imaging comparator such as computed tomography are needed to further evaluate the significance of LUS on cavity detection. We would like to add our findings to the current evidence on this topic and stress that LUS on pulmonary aspergilloma is an interesting area to investigate further to explore US as a novel diagnostic option as timely, radiation-free, and cost-efficient imaging.