Clinical History
A 40-year-old male patient presented with a swelling above the right scrotum for 3 weeks. The swelling was non-tender, and non-progressive in nature. He gave no history of trauma or fever. On local examination a 1.5x1 cm swelling was present over the right scrotum, non-tender and firm in consistency.
Imaging Findings
Ultrasound of the scrotum (Fig.1 a, b & c) showed bilateral normal appearing right and left testes measuring 3.8x2.6 cm and 3.5x2.4 cm respectively with preserved vascularity. The bilateral epididymi were also normal in size and echotexture. Adjacent to the right epididymal head on the lateral aspect, a well-defined hypoechoic non-vascular lesion measuring 15x12 mm was noted having a whorled appearance with a central calcific focus with posterior shadowing, giving the lesion a "target" or "bulls eye" appearance. On MRI (Fig. 2 a, b & c), the lesion was isointense to the testis on T1-WI and hypointense on T2 and T2- STIR sequences. The central foci were hypointense on all sequences. The patient underwent excision biopsy (Fig. 3) of the right extra-testicular cyst.
Discussion
Epidermoid or epidermal inclusion cysts are rare benign tumours accounting for 1% of all testicular neoplasms, and the majority of the scrotal epidermoids that have been published in the literature have been located in the testis. Intrascrotal extratesticular epidermoids are extremely rare with only about 10 cases having ever been reported. They are most commonly seen between the second and fourth decade of life and unlike intratesticular epidermoids, which maybe hidden and discovered later, extratesticular scrotal epidermoids are detected earlier often as a palpable lump or nodule. They maybe unilateral or bilateral and can also be multiple. Genital extratesticular epidermoids may be found in any location from the distal penile frenulum up to the anal canal. Several theories regarding their pathogenesis have been proposed and these include: (a) an abnormal closure of neural groove or epithelial fusion lines; (b) traumatic implantation of epidermal tissue; (c) a single layer teratoma from germ cells; and (d) ectopic dislocation of a tissue into a neighbouring area. [1, 2]
Ultrasound is the first imaging modality of choice. Five characteristic sonographic patterns for epidermoids have been described by Lee et al. They were characterised as oval, tubular or lobular in shape and classified as (I) alternating hypoechoic and hyperechoic eccentric rings with an ‘onion skin’ appearance; (II) target or ‘bulls eye’ lesion (hypoechoic lesion with a hyperechoic centre); (III) hypoechoic lesion with scattered echogenic reflectors; (IV) an inhomogeneous lesion; (V) areas of varying echotexture. The majority of the lesions shows no vascularity on colour Doppler. On MRI they appear as thin-walled lesions which are hypointense on T1 WI and hyperintense on T2 WI. Post gadolinium T1 weighted images show no enhancement, consistent with the avascular nature of the mass. MRI is also useful when ultrasound findings are confusing or inconclusive. It also delineates the scrotal structures clearly providing an anatomical road map for surgery. CT is not commonly used due to the risk of radiation-induced secondary cancer. Besides this, other advantages of MRI over CT include the ability of the former to effectively depict intra and extratesticular masses, describe various tissue types such as cysts, solid masses, fat and fibrosis. Tumour marker (AFP, beta-hCG and LDH) workup usually turns out to be within normal limits. [3, 4]
Differential Diagnosis List
Extratesticular scrotal epidermoid cyst
Teratoma
Other malignant tumors
Final Diagnosis
Extratesticular scrotal epidermoid cyst
