Some cyclists who find a firm lump between their legs learn it has an unforgettable nickname: the "third testicle." The condition, formally called perineal nodular induration, is a benign growth linked to repeated pressure and friction from a bicycle saddle. Now, a new study reports a consistent microscopic pattern that could help pathologists recognize it faster.
The study of eight patients, published in the American Journal of Dermatopathology, describes practical diagnostic clues for an uncommon lesion that can be mistaken for a tumor. The authors wrote that although the condition is clinically recognized, its appearance under the microscope had remained incompletely characterized.
A Lump with Many Nicknames
Perineal nodular induration is also known as cyclist's nodule, biker's nodule, ischial hygroma, and accessory testicle. It typically appears in the perineum, just behind the scrotum in men or near the sit bones, as one nodule or a pair on either side of the midline.
The nickname comes from where it sits and how it feels. Doctors believe repeated microtrauma from pressure, vibration, and shear forces on fat and connective tissue triggers the growth. A South African report describes the nodules as usually 2 to 3 centimeters in size and notes the condition has also been recorded in female horseback riders. The first description is credited to a 1988 report on two cyclists whose lumps were called accessory testicles.
The condition appears rarely in the medical literature. A 2024 review by a Swiss and German team found 23 cases described in 16 PubMed-listed articles published between 1990 and 2023, 14 in men and nine in women. About 30% were managed conservatively and 70% surgically. The reviewers noted that chronic lymphatic congestion may contribute, and they described a surgical approach that uses a fluorescent dye called indocyanine green to map and seal lymphatic vessels, aiming to lower the chance of the lump returning.
Women are not immune. A 2024 case report from France described a 47-year-old cyclist with vulvar swelling that went misdiagnosed for a year, noting that fewer than 25 cases of this female form, sometimes called bicyclist's vulva, have been reported.
What the Microscope Revealed
The new study reviewed tissue from seven men and one woman, ages 34 to 76, with a median age of 48.5. Two experienced dermatopathologists examined each case independently, using conventional microscopes and digital slide images.
Every sample showed a poorly defined fibrous, glassy proliferation centered in the deep skin and the fat beneath it. Other consistent features included heavy scarring of the connective tissue, trapped fat, few cells, bland spindle-shaped cells, and widened blood and lymph vessels. All eight samples also contained rounded nodules of hyalinized collagen, a pattern the authors say earlier reports had not specifically emphasized.
Special staining in two cases showed elastic fibers were markedly reduced or nearly absent. Extra immune-based stains, performed in two cases, were nonspecific.
The authors concluded that this reproducible pattern may let pathologists recognize the condition on routine slides in the right clinical setting, potentially reducing the need for extra testing in some cases. The study is small and retrospective, which reflects how rarely the lesion is biopsied.
When a Saddle Sore Becomes a Mass
Many cases are managed without surgery. A 2020 clinical report in Deutsches Ärzteblatt International described a 62-year-old man whose pressure-sensitive perineal swellings had grown and become permanent. The authors called a break from cycling the treatment of choice, suggested a gel saddle as an alternative, and said steroid or hyaluronidase injections could be considered in particularly severe cases.
The South African authors, who described one patient treated with surgery and another managed conservatively with the help of saddle pressure mapping, concluded that both approaches can succeed and that no single treatment is best for everyone.
Some lumps grow large. University of California, San Francisco surgeons reported the case of a healthy cyclist whose lump enlarged over five years into a perineal mass that kept him off his bike. Surgeons removed a mass measuring about 14 by 5 centimeters, and he returned to cycling.
Why a New Perineal Lump Still Needs a Doctor
The benign nature of a cyclist's nodule does not mean every lump in that area is harmless. Under the microscope, it can resemble several soft-tissue tumors, and imaging, sometimes followed by a biopsy, helps sort out the possibilities. In a 2017 letter responding to the San Francisco case, urologists cautioned that in male cyclists, problems of the urethra, the tube that carries urine, can occasionally present as a perineal mass, and that asking specifically about cycling and urinary symptoms can help tell them apart.
Cyclists who notice a new, growing, or painful lump in the saddle area should have it examined by a clinician. For those diagnosed with the condition, saddle changes, padding, and time off the bike are often the first steps.
Key Questions Answered
What is a cyclist's nodule?
It is a benign lump of fibrous tissue in the perineum linked to repeated saddle pressure, vibration, and friction. Its formal name is perineal nodular induration.
Why is it called a third testicle?
In men, it often sits just behind the scrotum and can feel like an extra testicle.
What did the new study find?
Pathologists reviewing eight cases found a consistent pattern, including rounded nodules of hyalinized collagen in every sample and bland, sparse cells.
How is it treated?
Often with a break from cycling, saddle changes, or injections. Large or persistent lumps may be surgically removed.
Should cyclists worry about every lump?
No, but a new or growing lump should be checked by a doctor, because other conditions can look similar.
Published by Medicaldaily.com
