Radiographical Spectrum of High-altitude Pulmonary Edema: A Pictorial Essay

DISCUSSION

The diagnosis of HAPE as per Lake Louise criteria is based on pulmonary symptoms and signs.⁶ HAPE may present as cough, initially dry progressing to a productive cough, which may have whitish or blood-tinged sputum. Breathlessness (out of proportion to the amount of exertion), orthopnea, and chest pain are also seen. On examinatin, tachypnea, tachycardia, wheeze, and crackles on auscultation are noted. Often, these cases occur at remote locations with no access to necessary medical facilities. Delay in evacuation to the nearest healthcare facility can be detrimental to the patient. Making a timely correct diagnosis, therefore, assumes utmost importance.

Radiology remains a crucial cornerstone in the diagnosis and management of HAPE. These patients can have clinical–radiological discordance. Lung ultrasonography is a crucial evolving tool in diagnosing HAPE earlier, and its portability can help in field settings in the future.⁷ We have demonstrated different radiographical manifestations of HAPE. Several differentials for these radiographical patterns are tabulated in Table 1. Reports suggest radiographic evidence of early pulmonary edema even after prolonged high-intensity exertion at HA underlining the importance of chest radiography in this setting.⁸ Vock et al. also noted many different radio-morphological pictures in HAPE. Radiographic pictures may include unilateral or bilateral, central or peripheral, homogenous, or patchy fluffy opacities, predominantly in the dependent zones of lungs.⁹

Bilateral diffuse opacities is a common manifestation of HAPE seen in up to 40% patients by Vock et al., 81% patients by Li et al., and 85% patients by Kobayashi et al.⁹–¹¹ Airspace opacification is sharply confined to central, perihilar regions of the lung with sparing of peripheral or subpleural regions in early cases and extending to the periphery in severe cases.¹²,¹³ It is essential to rule out differentials as all the patients with bilateral diffuse radiological opacities at HA need not be HAPE, as was reported in a patient of systemic lupus erythematosus with diffuse alveolar hemorrhage.¹⁴ Drowning or immersion pulmonary edema can mimic HAPE with bilateral diffuse opacities.¹³,¹⁵

Cardiogenic pulmonary edema is by far the commonest differential of HAPE (Figs. 1 and 2). The presence of an underlying heart disease, bilateral pleural effusion, and cardiomegaly should arouse the suspicion of this differential. Pleural effusion is rarely seen in HAPE but may be seen when patients have delayed presentations. It is vital to interpret cardiomegaly correctly in an anteroposterior film as may be required on certain occasions when a patient is too critical for a routine standing PA film. Increased cardiothoracic ratios have been reported in HAPE even in the absence of overt cardiogenic edema, especially right ventricle and prominence of the pulmonary vasculature (acute cor pulmonale), which rapidly reverses on recovery.¹⁰,¹⁶,¹⁷ Pulmonary hypertension may be appreciated as prominence of the pulmonary trunk (increased bulge below the aortic knuckle at the left mediastinal border) and central pulmonary arteries with peripheral pruning and enlargement of right descending pulmonary artery (interlobar artery) (Figs. 2, 3 and 5). Most importantly, for the same degree of radiological involvement or hypoxia, a patient with cardiogenic pulmonary edema is much more symptomatic than a patient with HAPE.

Less commonly, the opacities may be more diffuse without any central predilection (Fig. 3), as seen in most cases of acute respiratory distress syndrome and often in viral pneumonia and several noninfective interstitial pneumonitides (Table 1).

Unilateral pulmonary edema as a radiological presentation has been reported in HAPE previously, as also illustrated in Figures 4 and 5 above.¹⁸–²⁰ Predominantly unilateral radiographic involvement was variably reported from 15 to 60%.⁹–¹¹ Right lung predilection and predominance were shown in patients with unilateral and bilateral edema, respectively.⁹,¹¹ Since HAPE presenting as unilobar or multilobar consolidation is rare, it is imperative to be aware of such a radiological picture (Figs. 6 to 10). Rounded opacities that may be misinterpreted as metastasis can sometimes be seen (Figs. 8). The mechanism of HAPE is uneven sheer stress of pulmonary capillaries along with capillary stress failure in areas of heterogeneous and over-perfused capillaries. Owing to the apicobasal pressure gradient, commonly involved zones are lower lung zones, i.e., the dependent zones. However, it is not unusual for HAPE to involve upper or mid-zone, as seen in Figure 10, and in endemic areas can mimic tuberculosis. In any given individual developing recurring HAPE, there is no predilection to any specific zone, as was reported by Kobayashi et al. in a patient with recurrent HAPE.¹⁰ There is no clear pathophysiological mechanism for atypical findings of HAPE. Some authors, though, have suggested a prior trauma or damaged lung tissue as a cause for zone predilection, but the same has not been proven. Asymmetrical perfusion due to a variety of causes like unilateral pulmonary artery agenesis/hypoplasia or unilateral embolism, prolonged lateral decubitus positioning, and cardiac disorders, mainly mitral regurgitation, have been suggested as plausible mechanisms for unilateral pulmonary edema in HAPE. Though none of the patients described in this manuscript had any forthcoming history, clinical findings, or echocardiography features to suggest any of the above.¹⁸,¹⁹,²¹–²⁴

The clinical presentation of HAPE can overlap with a broad spectrum of cardiopulmonary diseases. While HAPE can be managed by supplemental oxygen therapy and bed rest with minimal or no pharmacotherapy, more severe disorders like PTE and CAD need urgent specialist care.⁴ Special caution is required in differentiating pneumonia from HAPE to avoid unnecessary overuse of antibiotics. Owing to the clinical overlap between HAPE and other cardiopulmonary conditions, relying solely on radiographic findings without emphasis on history and examination can lead to wrong diagnosis and poor outcomes. Despite severe hypoxia, HAPE patients do well with oxygen therapy and other conservative measures. Correct diagnosis can avoid unnecessary intubation and other potentially harmful therapeutic measures. A systematic approach is, therefore, warranted in all patients with suspected HAPE while maintaining a low threshold to seek specialist care. Such an approach has been described in detail in the supplement attached.

This study is limited by the relatively poor quality of radiographs with no incidence calculation of different radiological patterns, and the lack of supporting CT scan images. Most areas at such altitudes lack in healthcare infrastructure, and advanced imaging technology is often not available.