Paraganglioma classification
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Asem Juhani, M.D.[2]
Overview
Pheochromocytomas and paragnagliomas (collectively referred to as PPGLs) are rare tumors that originate from chromaffin cells in the adrenal medulla (pheochromocytoma) and extra-adrenal neural ganglia (paraganglioma). These tumors can be biochemically active (producing catecholamines) or silent. PPGLs can also be classified as either sporadic or familial, with association extablished to several familial syndromes.
PPGLs can be either benign or malignant. However, the definition of malignancy is established by the presence of metastasis as benign and malignant tumors in this category are indistinguishable in their histological and biochemical characteristics. Extent of spread of tumor is another factor that classifies PPGLs, putting them into the categories of local, regional and metastatic.
Classification
There are several way to classify pheochromocytomas and paragangliomas (PPGLs), including:
Origin of Tumor
PPGLs may be classified according to their site of origin into:
- Pheochromocytoma: tumor originates from chromaffin cells in the adrenal medulla. (80-85%)
- Paraganglioma: tumor originates from chromaffin cells in extra-adrenal neural ganglia. (15-20%) These can have a sympathetic origin (sympathetic chain in thorax, abdomen and pelvis) or a parasympathetic origin (in neck, head and skull base).
Extent of Spread
Both pheochromocytomas and paragangliomas may be classified into 3 subcategories based on spread:
- Local.
- Regional.
- Metastatic.
These 3 categories share the same histological and biochemical characteristics. Metastasis is considered the definition of malignancy in PPGLs. Non-metastatic PPGLs are considered benign.
Biochemical Profile
Most PPGLs are biochemically active, producing varying amounts of catecholamines like epinephrine, norepinephrine and dopamine, but rarely, they can be biochemically silent.
For pheochromocytomas (adrenal tumors) , the split is halfway between tumors with adrenergic phenotype and those with a noradrenergic phenotype (half adrenergic, half noradrenergic). Paragangliomas (extra-adrenal tumors) that arise from sympathetic ganglia produce noradrenaline (predominantly or even exclusively), while those in the head and base of skull don't usually produce catecholamines save for some dopamine and its metabolite 3-methoxytyramine.