The babirusa (in the pig family) has four large tusks. This old male has grown one tusk so long that it impaled his own skull, perhaps fatally. 
From Tetrapod Zoology.

The babirusa (in the pig family) has four large tusks. This old male has grown one tusk so long that it impaled his own skull, perhaps fatally. 

From Tetrapod Zoology.