Obliquely oriented superior accessory fissure of the lower lobe of the lung: CT evaluation of the normal appearance and effect on the distribution of parenchymal and pleural opacities.

PURPOSE: To review computed tomographic (CT) and radiographic features of an oblique superior accessory fissure in the lower lobe of the lung. MATERIALS AND METHODS: CT scans in 34 patients with a prospectively identified accessory fissure of the lower lobe were reviewed and correlated with chest radiographs (31 patients). The fissure and its relationship to segmental bronchovascular structures were evaluated on transverse scans. Three-dimensional (3D) shaded surface display (SSD) reconstructions were obtained from spiral volume data (six patients). RESULTS: Thirty-four patients had 36 accessory fissures (26 right, 10 left). Four of the 36 accessory fissures were manifested by a normal fissure line; two, by slight thickening or minimal linear atelectasis; 16, by thicker linear or subsegmental atelectasis; two, by contiguous tumor infiltration; one, by adjacent consolidation; and 11, by intrafissural extension of pleural fluid. Analysis of bronchovascular structures revealed that this fissure was the superior accessory fissure. The 3D SSD reconstructions demonstrated an oblique orientation. On frontal radiographs, presence of this fissure correlated with a curvilinear band of atelectasis coursing inferomedially and obliquely from its intersection with the lateral aspect of the major fissure toward the infrahilar region on the right and the heart border on the left. Chest radiographs also showed intrafissural extension of pleural fluid. CONCLUSION: A superior accessory fissure of the lower lobe, more common on the right than on the left, can be identified at transverse CT. Contrary to previous descriptions, it may be oblique, as findings on transverse images suggest and 3D SSD reconstructions confirm. Its presence correlates with characteristic patterns of atelectasis and pleural fluid collection on conventional radiographs.

Maximal contraction lessens impact response in a muscle contusion model.

The effect of muscle contraction on a contusion injury model was studied in the gastrocnemius muscle of anesthetized rats. Both limbs of 18 rats received a contusion injury with a blunt non-penetrating impact. One hind limb was relaxed during impact and the other was electrically stimulated to tetanic contraction. The impact was produced using a drop-mass technique (mass = 171 g, height = 101 cm, spherical radius of impactor tip = 6.4 mm). The impact response was determined by sampling (10 kHz) the transmitted impact force and the displacement of the impactor. In a subgroup of nine rats, the severity of the contusion injury was measured by recording contractile tension in twitch and tetanus within two hours of injury. We found that the peak impact force was significantly less (p < 0.01), while the peak impact displacement was significantly greater (p < 0.01) in the contracted limb. Correspondingly, the impact stiffness of the contracted limb was significantly less (p < 0.01) than the impact stiffness in the relaxed limb. Both impacts produced significant injuries relative to an uninjured control group. The tetanic tension (31 +/- 4 N) generated by the muscles that were contracted during impact was significantly (p < 0.03) greater than that generated by the muscles that were relaxed during impact (27 +/- 4 N). The findings from this specific model indicate that the impact response of the limbs with relaxed muscle was dominated by the underlying bone, while maximally contracted muscle decreased the influence of the bone and lessened the impact response. Maximally contracted muscle was not more susceptible to injury and may act as protective mechanism against some impacts.