The Chapel Hill Consensus sorts vasculitis by the dominant calibre of vessel involved. Reading the options against that scheme:
$\text{Leukocytoclastic} \rightarrow$ small (postcapillary venules)
$\text{GPA} \rightarrow$ small (ANCA-associated)
$\text{MPA} \rightarrow$ small (ANCA-associated)
$\text{PAN} \rightarrow$ medium muscular arteries
Polyarteritis nodosa is the textbook necrotising arteritis of medium-sized muscular arteries, characteristically ANCA-negative and linked to hepatitis B, sparing the lungs. The other three sit in the small-vessel compartment.
\[\boxed{\text{PAN is the medium-vessel vasculitis}}\]