Other Penile Variations
Narrowing of the penile shaft as a result of injury
Such injuries usually occur when the penis is engaged in vigorous sex and rams head-on into some hard obstacle. The resulting bleeding in the erectile chambers of the penis causes scar formation; because this scar tissue cannot expand in the same way as the rest of the penile chamber, a constriction develops on erection.
An unusually prominent glans
Some men have a glans which is by far the widest part of their penis. You can see this in the picture below. There is no anatomical or medical significance to this, but such a prominent head can produce very satisfying feelings for a woman during intercourse.
Narrowing of the penile shaft around the base of the glans
This may be natural, or it may be the result of injury. It often occurs in cases of hypospadias.