Neurogenic tumors are a diverse group of growths arising from the cells of the nervous system. The term “neurogenic” refers to their origin in neural tissue, including the peripheral and sympathetic nervous systems. This category encompasses a wide spectrum of tumors, ranging from common, slow-growing, non-cancerous masses to rare, aggressive malignancies. Understanding these tumors requires looking closely at the specific cell types from which they originate.
Understanding the Cellular Origin
Neurogenic tumors are defined by the specific cells within the nervous system that undergo uncontrolled division. These cells originate primarily from the neural crest, a transient group of cells in the developing embryo that gives rise to much of the peripheral nervous system (PNS). The resulting tumors generally fall into two main cellular categories: those from nerve sheath cells and those from developing neurons, or ganglion cells.
Tumors arising from the nerve sheath involve the cells that insulate and support the nerve fibers. The most common of these are Schwann cells, which form the myelin sheath around PNS axons, and their resulting tumors are often benign. Other nerve sheath tumors can originate from perineurial cells or fibroblasts that are also part of the nerve structure.
Tumors of the sympathetic nervous system (SNS) originate from precursor cells that mature into ganglion cells or chromaffin cells. These precursor cells are called neuroblasts, and tumors arising from them are neuroblastic tumors. The SNS is a division of the autonomic nervous system, responsible for the body’s “fight or flight” response. SNS tumors can sometimes produce hormones that affect the body’s function.
Categorizing Neurogenic Tumor Types
The broad group of neurogenic tumors is classified primarily based on their specific cell of origin and their potential for malignancy. The two largest categories are peripheral nerve sheath tumors and sympathetic nervous system tumors.
Peripheral Nerve Sheath Tumors (PNSTs) are the most common type and arise along the vast network of nerves outside the central nervous system. Schwannomas are the most frequent PNST in adults, typically benign, slow-growing, and forming from Schwann cells. Neurofibromas are another common benign type, often composed of a mixture of cell types including Schwann cells, fibroblasts, and perineurial cells.
The malignant form of this group is the Malignant Peripheral Nerve Sheath Tumor (MPNST), a rare and aggressive cancer. Plexiform neurofibromas, a subtype of neurofibroma, carry a higher risk of transforming into MPNST, particularly in individuals with the genetic condition Neurofibromatosis Type 1 (NF1).
Sympathetic Nervous System Tumors arise from the chain of ganglia or the adrenal medulla, which are part of the SNS. Neuroblastoma is an aggressive malignant tumor that most commonly affects infants and young children. It arises from immature neuroblasts and is the third most common pediatric malignancy in the United States.
Ganglioneuroma represents the fully matured and almost always benign form of a neuroblastic tumor. Ganglioneuroblastoma is an intermediate form, containing a mixture of mature ganglion cells and immature neuroblasts, giving it a variable malignant potential. Pheochromocytoma is a tumor that typically arises in the adrenal medulla from chromaffin cells, which are specialized neuroendocrine cells.
Primary Locations and Symptomatic Presentation
Neurogenic tumors can occur anywhere there are nerves, but they show a strong preference for specific areas of the body outside of the brain. A common location for these tumors is the posterior mediastinum (the space in the chest cavity behind the heart and between the lungs). Tumors here, such as Schwannomas and Neurofibromas, often grow along the spinal column where nerve roots exit.
Another frequent site is the abdomen, specifically the retroperitoneum, which is the space behind the abdominal lining. Tumors in this area often follow the distribution of the sympathetic ganglia, with the adrenal glands being a common origin, especially for Neuroblastoma and Pheochromocytoma. Tumors can also arise along peripheral nerves in the limbs, neck, and head.
When tumors grow, they cause symptoms primarily by compressing surrounding structures (nerves, blood vessels, or organs). This mechanical pressure can lead to localized pain, a tingling sensation known as paresthesia, or numbness. If the tumor is near a motor nerve or the spinal cord, it can cause muscle weakness or functional deficits, such as difficulty walking or breathing.
In some cases, particularly with Pheochromocytoma, the tumor is metabolically active, producing hormones called catecholamines. This overproduction results in systemic symptoms such as sudden, severe headaches, heart palpitations, and high blood pressure. Most neurogenic tumors in adults, however, are often found incidentally during imaging for unrelated conditions, as they are frequently asymptomatic.
Methods of Identification and Management
The process of identifying a neurogenic tumor typically begins with imaging studies to locate and characterize the mass. Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) scans are the primary tools used to visualize the tumor, assess its size, and determine its relationship to nearby nerves and the spinal cord. MRI is particularly useful for evaluating potential extension of the tumor into the spinal canal.
A definitive diagnosis requires a tissue sample obtained through a biopsy. This procedure, often involving a fine or core needle, allows a pathologist to examine the cells, determine the exact tumor type, and distinguish between benign and malignant forms. For tumors like Pheochromocytoma, blood and urine tests that measure hormone levels are also an important part of the diagnostic workup.
The mainstay of treatment for most neurogenic tumors is surgical excision. If the tumor is benign but symptomatic, or if malignancy is suspected, the goal is complete removal while preserving nerve function. For malignant tumors, such as MPNST and Neuroblastoma, surgery is often combined with chemotherapy or radiation therapy, which are used to shrink the tumor before surgery or treat remaining cancer cells afterward.