Testicular epidermoid cysts: a reevaluation
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Testicular epidermoid cysts (TECs) are rare benign testicular neoplasms. As TECs are rarely associated with germ cell tumours (GCTs), the understanding of biological behaviour and clinical management of TEC is unresolved.
We retrospectively searched the files of patients treated for testicular neoplasms and germ cell cancer in the time from 2000 to 2017. Those with TEC were subjected to closer review looking to clinical and histological features, and to results from imaging with ultrasonography (US), contrast enhanced sonography (CEUS) and magnetic resonance imaging (MRI).
Among 589 patients undergoing surgery for testicular tumour, nine simple TECs were identified (1.5, 95% confidence intervals 0.53–2.50%). Median age was 26 years. Imaging revealed sharply demarcated roundish lesions with avascular central areas. Eight patients underwent testis-sparing excision with no recurrence ensuing. One had orchiectomy because of large size of the mass. Histologically, TECs consisted of cornifying squamous cell epithelium and no accompanying germ cell neoplasia in situ. Two additional cases (0.3% of all) required orchiectomy because these TECs were associated with ipsilateral GCT.
TEC is usually a benign lesion that can safely be diagnosed with US, CEUS and MRI due to its roundish shape and its avascular centre. Histologically, this TEC corresponds to the prepubertal-type teratoma unrelated to germ cell neoplasia in situ of the 2016 WHO classification. The other subtype of TEC that is associated with invasive GCT represents a teratoma of postpubertal-type. From a clinical point of view it could be easier to differentiate between a “simple TEC” which is benign (prepubertal type) and a “complex TEC” which is malignant because of its association with invasive GCT.
KeywordsTesticular neoplasm Germ cell tumour Epidermoid cyst Testis sparing surgery Scrotal sonography
Testicular epidermoid cysts have been first reported in 1942 , but their histogenetic origin has been a matter of dispute ever since. Accordingly, clinical management has been a matter of controversy, likewise. In the recent WHO classification of 2016, testicular epidermoid cysts (TECs) are listed as teratoma of prepubertal type within the group of germ cell tumours unrelated to germ cell neoplasia in situ . The ICD-O code 9084/0 denotes a benign behaviour of this neoplasm. However, TECs have also been documented as part of invasive testicular germ cell tumours (GCTs).Therefore it has been hypothesized that two different types of TECs exist, one a truly benign “simple” testicular EC and the other a “complex” TEC associated with GCT thus representing teratoma . Due to the rarity of TECs there are only few systematic clinical evaluations available [4, 5, 6]. Most of the current knowledge is based on small clinical series and single case reports. To improve the over-all understanding of TECs we retrospectively reviewed our experience with simple TECs and with complex ECs.
We retrospectively searched the files of all patients who underwent treatment for testicular neoplasms or germ cell cancer in the department of urology in Albertinen-Krankenhaus Hamburg in the time from January 2000 to March 2017. We looked into the histologies of the patients operated on testicular tumours and selected those with TEC for closer review. The relative incidence of TECs in relation to GCTs was determined by calculating proportions with 95% confidence intervals. Median age and side-localization of TECs were compared to findings in GCTs. Clinical and histopathological features as well as imaging findings of the TEC patients were tabulated and descriptively analysed. Ethical approval was given by the institutional ethical committee (Albertinen Ethikkommission: U3–2015).
Follow-up is available in 7 patients with simple TEC. All of whom are well with no local recurrence after an average time-intervall of 6 years after surgery. One patient succumbed to cardiac failure, one was lost to follow-up.
Simple TEC is a rare but well-known lesion. As shown herein, TECs account for only 1.5% of all testicular neoplasms among post-pubertal men. This figure corresponds well with the 2.1% frequency reported previously [4, 5, 7] but it is clearly lower than the 10% relative incidence reported in a series from Taiwan . Ethnic predisposition may account for that striking difference.
TECs have many clinical characteristics in common with GCT: Particularly clinical presentation with painless mass , the age predisposition of early adulthood and the preponderance of the right side. All these features were confirmed in our series. Reportedly, patients with TEC may have exceptionally long symptomatic intervals [10, 11]. Accordingly, two of our patients had noted a testicular nodule for as long as 10 and 13 years before surgery, respectively.
Usually, the diagnosis can be safely made with B-mode scrotal ultrasound. The typical onion-ring phenomenon is present in about 60% of all cases [12, 13]. The cyst-like appearance and the roundish configuration are further typical findings of the present and previous series [8, 14, 15]. A more distinctive finding is the absence of vascularization of the cyst core documented with CCDS (colour-coded duplex sonography) and CEUS as shown in four of our cases and previously reported by others . Scrotal MRI can likewise detect these morphologic features [17, 18]. The avascular nature of the cyst core is safely shown by the absence of signal enhancement after application of gadolinium-based contrast material [19, 20, 21]. This finding was confirmed in all 7 patients of our series undergoing MRI.
Local excision (TSS) is the treatment of choice for TEC as realized in 8 of our patients. Orchiectomy is exceptionally required in cases with a large mass and only little remaining testicular tissue. Accordingly, one of our cases underwent orchiectomy. Similar cases are reported [6, 11]. Recurrences after TSS have not yet been experienced until now and the same is true for 7 of our patients in whom follow-up is available.
Histopathological findings in our series fully accord with previous reports. The lesion typically consists of a well-defined cyst lined by a fibrous membrane and filled with layers of cornifying squamous epithelium and cell debris. No skin appendages are found in the cyst’s lumen and no GCNis is present in the adjacent testicular parenchyma [22, 23].
The most striking finding of the present series is that simple TEC can obviously be mimicked by epidermoid cysts developing in association with full-blown GCT . The association of TEC with ipsilateral GCT has been reported sporadically to date [3, 7, 25, 26]. The association of GCT with contralateral TEC has also been noted . Urologic surgeons should be aware of the risk of concomitant GCT when conducting TSS of TEC. Therefore tumour marker measurements should be done preoperatively as is recommended for the examination of any scrotal mass . As previously documented, the novel marker miR-371a-3p can substantially aid in diagnosing equivocal testicular masses . Accordingly, miR371a-3p was elevated in both cases with complex TECs but not in the 3 cases with simple TEC. Frozen section examinations during TSS could be valuable for intraoperative assessment of the cyst [29, 30].
Since the first description of TEC by Dockerty and Priestly in 1942  the histogenesis of the lesion remained poorly understood. Many clinical features, particularly age of predisposition, association with undescended testis and preponderance of the right side favour the origin from teratoma. Other findings (mainly the absence of GCNis and the very slow growth rate) argue against this theory. The WHO 2016 Classification System of Tumours defined TEC (and some other rare entities) as a specialized form of prepubertal-type teratoma that is unrelated to germ cell neoplasia in situ”  and that may occur in adulthood, too. Similarly, other prepubertal types of teratoma have been documented to sporadically occur in adult patients . Thus, the simple TECs reported herein would represent teratomas of prepubertal type as described in 2016 WHO classification. The two cases with “complex TECs” reported herein would represent teratomas of postpubertal type (ICD-O 9080/3) according to the WHO classification with the “/3″ coding for malignancy. This type of epidermoid cysts thus represents a specialised differentiation of teratoma analogous to the development of other benign structures within teratomas, e.g. hairs or teeth. The two types of TECs can be clearly differentiated with regard to the histogenesis according to the WHO classification. However, from a clinical point of view, this differentiation is not really advantageous. Therefore, it is suggested to define two distinct classes of TEC, clinically, the first representing the more common “simple TEC” without malignant features (i.e. without accompanying GCNis) and the second encompassing the “complex TEC” cases with accompanying GCT.
Testicular epidermoid cysts may occur in two different forms, the benign subtype, called “simple TEC”, clinically, and the other subtype representing an epidermoid cyst that occurs in association with invasive germ cell tumours (GCNIS), called the “complex TEC”, clinically. Urologic surgeons must be aware of the second type because conservative surgery would be inappropriate in these cases.
Availability of data and materials
Currently, the data will not be shared, there are further investigations in progress.
AP: study design, data collection, manuscript writing, data analysis, management, revision management. KJ: data collection and analysis. SE: data collection and analysis. HD: data collection and analysis. BF: data collection and analysis. MS: data analysis. LG: data collection and conception. DKP: study design, data collection, supervison, management, revision management. All authors read and approved the final manuscript.
Ethics approval and consent to participate
Ethical for this retrospective study was given by Albertinen Ethik Kommission (U3–2015). Informed verbal consent was obtained from all individual participants included in the study. The institutional ethical committee approved this procedure because only archival material was investigated and personal identities of the patients were only disclosed to the principal investigator (AP) and the senior author (DKP) of the project.
Consent for publication
The authors declare that they have no competing interests.
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