There are a number of abnormal sperm morphologies.
- Abnormal heads can include enlarged head, double head, round head, constricted head, amorphous head, pinhead, and acute tapering forms. There are also heads with abnormal numbers of vacuoles (>2 in the acrosomal region and/or vacuoles in the post-acrosomal region are abnormal).
- Midpiece abnormalities include distended and thin midpiece regions.
- Abnormal tails include short tail, double, triple or multiple tails, coiled tail, broken tail, or absent tail.
- Cytoplasmic droplets are also seen in some specimens. These are large regions of cytoplasm just below the head, assumed to represent failure of complete sperm maturation or a sign of either toxicity or oxidation. There have also been reports that cytoplasmic droplets may be artifacts from the fixation and staining for morphology analysis.
WHO 5th edition contains multiple examples of normal sperm and borderline/abnormal variations that cause a sperm to be classified as abnormal. It is an excellent resource.