The identification of H3F3A mutation in giant cell tumour of the clivus and the histological diagnostic algorithm of other clival lesions permit the differential diagnosis in this location

Table 1 Histology-based diagnostic algorithm of the main lesions arising within the clivus

	Histological appearance		Immunostaining pattern
	Gross examination	Microscopic appearance	S100	EMA	Keratin	Vimentin	Brachyury	CD3	CD20	CD45
Chordoma	Soft, haemorrhagic and grey lobulated tumour	Large cells with vacuolated cytoplasm	Yes	Yes	Yes	Yes	Yes	No	No^b	No^b
Chondrosarcoma	Hard, grey-white lobulated and cartilaginous mass	Large bubbly-looking cells with stellate-shaped nuclei	Yes	No	No	Yes	No	No	n/a	n/a
Meningioma	Round and well circumscribed mass attached to the dura	Syncytial cells with eosinophilic cytoplasm and vesicular nuclei	Yes	Yes	Yes^a	Yes	No	No	n/a	No^b
Osteosarcoma	Bulky, grey-white mass with areas of haemorrhage	Spindle cells producing eosinophilic matrix (osteoid). 25% show osteoclast-like giant cells	Yes	No	No	Yes	No	No	No^b	No^b
Pituitary adenoma	Soft, cream-colored tumour from the sella turcica, usually invading adjacent structures	Round cells with eosinophilic cytoplasm and spherical nuclei	No	No	Yes	Yes	No	No	No^b	No^b
T-cell Lymphoma	Well circumscribed tumour mass, resembling inflammatory lesions	Highly vascularized tumour with small and round cells	No	No	No	Yes	No	Yes	No	Yes
B-cell Lymphoma	Well circumscribed tumour mass, resembling inflammatory lesions	Highly vascularized tumour with small and round cells	No	No	No	Yes	No	No	Yes	Yes
Plasmacytoma	Soft and lobulated tissue, slightly pink- or cream-colored	Sheets of mature and immature plasma cells, with eccentric nuclei and “clock-face” chromatin	No	Yes	Yes	Yes	n/a	No	No	No

^aSeventy-five percent of malignant meningioma express cytokeratin; while no expression was found in benign meningiomas [60]
^bThe negative staining refers to neoplastic cells. Immune infiltrating cells can be responsible for a positive staining

ISSN: 1471-2407