It is generally not difficult for physicians to diagnose typical HAPE, which is based on medical history, symptoms, and signs including white, yellow, or pink frothy sputum, moist rales on pulmonary auscultation, and flocculent shadows on chest X-rays. However, atypical HAPE is much more difficult to diagnose. Patients usually develop atypical HAPE at altitude <3000 m, which may occur several days or longer after ascending to altitude. Symptoms differ from those of typical HAPE, such as less sputum or an absence of sputum and nonspecific findings on chest X-rays. Based on a previous study [6] , the development of HAPE can be classified into two stages from the onset to the presence of typical symptoms. The early stage is characterized by 2 Pulmonary Medicine interstitial pulmonary edema while the late stage is characterized by alveolar pulmonary edema. Patients with interstitial pulmonary edema do not usually exhibit serious dyspnea or typical signs such as pink frothy sputum, extensive moist rales, or wheezy phlegm. Thus, these patients are susceptible to misdiagnosis and delayed treatment. Li et al. [7] investigated the characteristics of HAPE in 482 patients. They examined the clinical symptoms and signs, and performed routine blood tests, electrocardiography, color Doppler echocardiography, chest X-rays, and computed tomography (CT) of the patients. They found that HAPE patients exhibited significant differences in these parameters compared with non-HAPE patients, and that the symptoms and signs were more obvious in HAPE patients than in non-HAPE patients. In addition, studies have revealed that oxygen treatment is more effective in HAPE than in other forms of lung injury. Therefore, some researchers have proposed that tentative oxygen treatment can be used for the early diagnosis of HAPE. Nevertheless, the most important examinations for the early diagnosis of HAPE are chest X-rays or CT. On chest X-rays, HAPE often presents as decreased pulmonary transmittance, increased or obscure lung markings, and ground glass-like changes in the lung, or patchy shadows. On CT scans, increased and enlarged lung markings, ground glass-like changes in the lung, nodule-like shadows, scattered or isolated alveolar edema of terminal bronchioles, and slim reticulate shadows can be observed.