The Diaphragmatic Crura and Retrocrural Space: Normal Imaging Appearance, Variants, and Pathologic Conditions

Abstract

The retrocrural space (RCS) is a small triangular region within the most inferior posterior mediastinum bordered by the two diaphragmatic crura. Multiplanar imaging modalities such as computed tomography and magnetic resonance imaging allow evaluation of the RCS as part of routine examinations of the chest, abdomen, and spine. Normal structures within the retrocrural region include the aorta, nerves, the azygos and hemiazygos veins, the cisterna chyli with the thoracic duct, fat, and lymph nodes. There is a wide range of normal variants of the diaphragmatic crura and of structures within the RCS. Diverse pathologic processes can occur within this region, including benign tumors (lipoma, neurofibroma, lymphangioma), malignant tumors (sarcoma, neuroblastoma, metastases), vascular abnormalities (aortic aneurysm, hematoma, azygos and hemiazygos continuation of the inferior vena cava), and abscesses. An understanding of the anatomy, normal variants, and pathologic conditions of the diaphragmatic crura and retrocrural structures facilitates diagnosis of disease processes within this often overlooked anatomic compartment.

Imaging the posterior mediastinum: a multimodality approach

“…For the same reason, inactive lesions have high-signal intensity on both T1-and T2-weighted images if there is fatty replacement (Fig. 4), or low signal intensity with iron deposition (12,21). Mild homogeneous enhancement on both CT and MRI is usually seen in active lesions, whereas a heterogeneous enhancing pattern is more common in inactive lesions because of iron deposition or fatty replacement (22).…”

“…Infection of a vertebral body may extend into the pre-and paravertebral soft tissues, spreading via the anterior or posterior longitudinal ligaments ( Fig. 3) (12,13).…”

“…Conversely, CT and MRI have a high sensitivity for detecting early osteolytic destruction of the vertebrae, accompanying focal or diffuse paraspinal soft-tissue abscess, intervertebral disc involvement, and epidural granulation tissue (4,12).…”

“…CT and MRI show well-defined, usually bilateral, paraspinal masses (Fig. 4), most commonly in the lower thoracic area (12). CT attenuation values and MRI signal intensity vary according to the grade of hematologic activity of the lesion.…”

“…On MRI, neuroenteric cysts have high signal intensity on T2-weighted images and are usually of low signal intensity on T1-weighted sequences, because they contain cerebrospinal fluid (12). MRI is essential in the workup of a suspected neurogenic cyst because it can depict each anatomic relation to the spinal canal.…”