Neurogenic mediastinal tumors

Nerve sheath tumors

These neoplasms frequently develop in the setting of systemic neurofibromatosis. The fundamental representative of this group is multiple neurofibromas.

• Location: Typically originate from the intercostal nerves (forming nodes in the subpleural divisions of the chest wall) or nerves of the middle mediastinum (in the subcarinal region).
• CT findings: On contrast-enhanced imaging, they are defined as low-density foci.

Plexiform neurofibromas require special attention due to the risk of malignant transformation (malignization). Upon transformation, the tumor rapidly increases in size, acquires lobulated contours, and may compress the airways.

MRI semiotics of a malignized plexiform neurofibroma:

1. T1-weighted imaging without fat suppression: a large mass lesion is visualized.
2. T1-weighted imaging with fat suppression (fat saturation): signal loss is noted, indicating the presence of a fat component within the node.
3. T2-weighted imaging: the tumor yields a high signal intensity.
4. Post-contrast T1-weighted imaging: intense contrast enhancement is recorded.

Sympathetic nervous system tumors

This group originates directly from nerve cells (sympathetic ganglia or adrenal tissue). It includes three main types varying in degree of aggressiveness:

• Ganglioneuromas: Benign nodes typical for children and young adults. On imaging, they appear as well-demarcated, vertically oriented ellipses spanning 3 to 5 vertebral bodies in length. On MRI, they yield a homogeneous intermediate signal on T1- and T2-weighted images.
• Ganglioneuroblastomas: Tumors with a variable degree of malignancy, also predominantly affecting the pediatric population. In 25% of cases, imaging methods reveal calcifications within them.
• Neuroblastomas: Highly malignant, aggressive tumors typical for children under 5 years of age. Unlike their benign counterparts, they have an extremely heterogeneous structure due to foci of necrosis, hemorrhage, cystic degeneration, and calcifications. They exhibit pronounced locally invasive growth and frequently cross the midline.

Mediastinal paragangliomas

Rare neuroendocrine tumors originating from chromaffin cells. Inside the chest cavity, they are divided into two subgroups:

1. Chemodectomas: Originate from the aortic body and are located near the aortic arch. As a rule, these are solitary nodes.
2. Pheochromocytomas: Account for less than 2% of all pheochromocytomas in the body. They may hide in the posterior mediastinum or have an intracardiac location (in the interatrial septum or left atrial wall).

About one-third of intrathoracic pheochromocytomas are non-functioning. The rest secrete catecholamines, producing a vivid clinical picture.

Diagnostic imaging: On radiographs and CT, these are rounded soft-tissue masses with an extremely rich vascular network (intensely enhancing with contrast). On MRI, their signal is comparable to muscle on T1-weighted imaging, but becomes very high on T2-weighted imaging. The gold standard for detection is scintigraphy with radioactive iodine (131I-MIBG) or somatostatin receptors, where increased radiopharmaceutical uptake is noted.

Non-neoplastic lesions of the posterior mediastinum

In the differential diagnosis of neurogenic tumors, it is important to remember conditions that can mimic them on radiographs:

• Lateral thoracic meningocele: A rare asymptomatic herniation of the meninges with CSF through the intervertebral foramen. Frequently associated with neurofibromatosis. On radiographs, it causes deformation of adjacent bones (indistinguishable from a neurofibroma), but CT and MRI unmistakably demonstrate the fluid nature of the node and its connection to the dural sac. CT with intrathecal contrast is used for confirmation.
• Extramedullary hematopoiesis: Occurs in patients with severe anemias (thalassemia, sickle cell anemia) as compensation for red blood cell deficiency. The bone marrow proliferates beyond the spongy bone, forming bilateral multiple lobular paraspinal masses in the lower parts of the chest cavity. On imaging, bones may have a characteristic lace-like pattern. Following successful anemia treatment, active red marrow in these foci undergoes involution and is replaced by fat and fibrosis.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Clinical manifestations and pathogenesis of catecholamine hyperproduction in mediastinal pheochromocytomas
• Specifics of MRI protocols for evaluating intracardiac paragangliomas
• Differential diagnosis of bone tissue alterations: lace-like pattern in anemias vs bone destruction in tumors
• Principles of using metaiodobenzylguanidine (131I-MIBG) in radionuclide diagnostics

Other topics in the «Chest Radiology» section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.