(pleural = hila.) — "lung root;" medusa-like tangle of arteries and veins on either side of the heart shadow. Irregular medial shadow in each lung where the bronchi and pulmonary arteries enter. Other structures in these areas, particularly lymph nodes, are normally so small as to be inapparent. The normal hilar shadow is almost entirely composed of the central pulmonary arteries. R hilar vessels seem to extend out farther than those on the L because a part of the L hilum is obscured by the shadow of the more prominent L side of the heart. The L hilum on a normal CXR is a little higher than the R one because of the slightly higher take-off of the L pulmonary artery.
(pl. hila, adj. hilate) ( Erdtman, 1952) Circular, indistinctly delimited, irregular aperture or thinning in spores. Examples: Aequitriradites verrucosus, Couperisporites tabulatus. Comment: This kind of feature is present in certain bryophytes and fungi and may occur on the proximal or distal face. See also: polumbra