Retrodiaphragmatic portion of the lung: how deep is the posterior costophrenic sulcus on posteroanterior chest radiography?

AIM: To determine the depth of the posterior costophrenic sulcus (CPS) on posteroanterior (PA) chest radiography in relation to the diaphragmatic dome and lateral CPS.
MATERIALS AND METHODS: Five hundred and forty consecutive PA chest radiographs that were performed for general health screenings were retrospectively reviewed. Among them 282 radiographs were selected that met the following criteria: visualization of the inferior boundary of the posterior CPS behind the right hemidiaphragm; and no abnormal findings that affected the shape and level of the diaphragm. The selected chest radiographs were from 155 men and 127 women with a mean age of 40.7+/-8.4 years. On 282 PA chest radiographs, the distances between the right diaphragmatic dome and posterior CPS (total diaphragmatic height), the diaphragmatic dome and lateral CPS (diaphragmatic dome height), and the lateral and posterior CPS (posterior CPS depth) were measured. In addition levels of the right lateral and posterior CPS were scored in relation to levels of the thoracic and lumbar spines. The relationships between the posterior CPS depth and demographic and physical data and other radiographic measurements were analysed.
RESULTS: The mean right posterior CPS depth was 29.2+/-15.6 mm. The average level of the posterior CPS in relation to the spine was 13.5+/-0.6, i.e., the level of lower half of the L1 vertebral body. The posterior CPS depth had a tendency to be deeper in those participants who were taller (r=0.17, p<0.01), had a higher body mass index (BMI; r=0.25, p<0.01), longer total diaphragmatic height (r=0.55, p<0.01), and shorter diaphragmatic dome height (r=-0.18, p<0.01).
CONCLUSION: As the posterior CPS is deeper than the lateral CPS by approximately 3 cm, and reaches, on average, to L1, the standard chest PA radiograph must include >3 cm below the level of lateral CPS, or should include the L1 spine.