Perineal nodular swelling in a recreational cyclist: diagnosis and discussion

DiagnosisThe diagnosis of a biker’s nodule was made, based merelyon the clinical history, the typical location and the imagingfindings.DiscussionAbiker’s nodule is a lesser known condition of the perineumthataffectscyclists.Thelesionhasbeenpreviouslyknownbymany synonyms, including ‘third or supernumerary testicle’,‘accessorytesticle’,‘perinealhygromaorinduration’[1–5]. Itis typically located in the paramedian region of the perineum,posterior to the scrotal sac, and is covered with normal skin.The size of the lesion rarely exceeds 3 cm [1–5].Symptoms include pain on pressure and when sitting onthe saddle, which often forces the athlete to give up ridingthe bicycle. On palpation, the nodule is solid andsometimes adherent to the adjacent soft tissue [2, 5]. Thelesion is believed to result from increased pressure,vibration and friction between the ischial tuberosities andthe hard saddle, characteristic of racing cycles or mountainbikes, with constant rubbing of the superficial perinealfascia against the bony structures [1–5].Histopathology shows a myxoid degeneration of thefatty tissue and collagen fibers overlying the ischialtuberosities, caused by necrosis of the superficial perinealfascia, sometimes with formation of pseudocysts [1–5]. Thelesion is not well vascularized [2].Imaging characteristics are only rarely reported. Ultra-sound shows a hypo-echoic nodule, with absence of anyincreased power Doppler signal [1]). Small internal cysticareas may be seen as well [1]. On computed tomography(CT), the lesion shows no uptake of contrast agent [3], whichis explained by the hypovascular nature on histology. To ourknowledge, magnetic resonance imaging (MRI) has not beenreported. As in CT, there is no uptake of contrast medium.The primary role of imaging is to determine the exact extentof the lesion. Ultrasound and MRI are particularly helpful inlocating the lesion in the subcutaneous fatty tissue and closeto the ischial tuberosities. In most clinical scenarios,ultrasound will suffice for imaging evaluation. Imaging hasan additional role in the differentiation between ‘biker’snodule’ and other causes of a perineal swelling. Thedifferential diagnosis [1, 3, 5] includes abscess, epidermalcyst, (cutaneous) adnexial mass, lipoma, and malignanttumor (soft tissue sarcoma or metastasis).In biker’s nodules, signs of inflammation or abscessformation are lacking, and the absence of contrast agentenhancement on MRI excludes malignancy.The primarytherapy consistsofavoidance ofthe causativefactor. Rest alone is generally not sufficient as therapy. Thecondition almost systematically imposes saddle adjustments