Paraganglioma microscopy
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Paraganglioma - Microscopic Features
H&E Appearance
(A) H&E: Nests of tumor cells (zellballen) separated by delicate fibrovascular septa. (B) Chromogranin IHC: Intense brown cytoplasmic positivity in chief cells, with pale sustentacular cells at nest periphery.
Architectural Pattern: Zellballen
The single most characteristic microscopic feature is the zellballen (German: "cell balls") pattern - compact nests or clusters of tumor cells separated by thin fibrovascular septa containing capillaries. This architecture mirrors the normal paraganglia from which the tumor arises. - Robbins, Cotran & Kumar Pathologic Basis of Disease, p. 694
Cell Types
Type I - Chief Cells (predominant)
- Origin: Neuroectodermal (neural crest derived)
- Shape: Round to oval; polygonal
- Cytoplasm: Abundant, clear or granular eosinophilic cytoplasm
- Nuclei: Uniform, round to ovoid; sometimes vesicular
- Ultrastructure: Contain dense-core cytoplasmic granules storing catecholamines. Two subtypes - light and dark cells - are distinguishable ultrastructurally
- Mitoses: Scant; pleomorphism does NOT reliably indicate malignancy
Type II - Sustentacular Cells (supporting)
- Shape: Elongated spindle cells resembling Schwann cells
- Location: Peripherally surround the chief cell nests
- Visibility: Difficult to identify on light microscopy; appear as spindle-shaped basophilic cells
- Function: Not fully elucidated, analogous to glial support cells
- Cummings Otolaryngology Head and Neck Surgery, p. 2221; Shambaugh Surgery of the Ear
Immunohistochemistry
| Marker | Cell Type Stained | Result |
|---|---|---|
| Chromogranin A | Chief cells (Type I) | Strongly positive |
| Synaptophysin | Chief cells (Type I) | Positive |
| INSM1 (insulinoma-associated protein 1) | Chief cells | Positive |
| CD56 | Chief cells | Positive |
| NSE (neuron-specific enolase) | Chief cells | Positive |
| S-100 protein | Sustentacular cells (Type II) | Positive (peripheral rim pattern) |
| GFAP | Sustentacular cells | Focal positivity |
| Cytokeratin | All cells | Negative (key differential point from carcinomas) |
| SDHB | All cells | Lost in SDHB-mutated tumors |
- Robbins p. 694; Harrison's 22E p. 3118; Cummings p. 2221
Electron Microscopy
Dense-core membrane-bound neuroendocrine granules (catecholamine-storing) are identifiable within chief cell cytoplasm. They are well-demarcated in paravertebral (sympathetic) tumors but tend to be scant in non-functioning tumors. - Robbins, p. 694
Predicting Malignancy - A Histological Challenge
Standard microscopic features are unreliable for predicting malignant behavior:
- Mitoses, pleomorphism, nuclear hyperchromatism, and even vascular invasion are not reliable indicators of malignancy
- Malignancy is defined by the presence of metastases (to regional nodes or distant sites), not by histology alone
- SDHB mutation is the strongest histological/molecular predictor - associated with 30-50% metastatic rates; demonstrated by loss of SDHB immunostaining (panel F above)
- Some studies suggest that a reduced ratio of sustentacular cells to chief cells (fewer S-100 positive cells) correlates with more aggressive behavior
- Robbins p. 695; Shambaugh Surgery of the Ear
Quick Reference Summary
| Feature | Finding |
|---|---|
| Architecture | Zellballen (nests separated by fibrovascular septa) |
| Main cell | Chief cell - round, abundant eosinophilic granular cytoplasm |
| Supporting cell | Sustentacular cell - spindle, peripheral, S-100+ |
| IHC chief cells | Chromogranin+, Synaptophysin+, INSM1+, CD56+ |
| IHC sustentacular | S-100+, GFAP focal |
| Cytokeratin | Negative |
| Malignancy marker | SDHB loss (IHC) |
| Mitoses | Scant; not predictive of malignancy |
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