Transurethral anatomical enucleation of the prostate with Tm:YAG support (ThuLEP): Evolution and variations of the technique. The inventors' perspective

After its introduction, transurethral anatomical enucleation of the prostate with Tm:YAG support (ThuLEP) has evolved as one of the standard techniques of transurethral anatomical endoscopic enucleations of the prostate. Growing evidence has proven ThuLEP as an alternative for the treatment of bladder outlet obstruction caused by benign prostatic enlargement and has been acknowledged by the EAU Guidelines on Management of Non‐Neurogenic Male Lower Urinary Tract Symptoms, incl. Benign Prostatic Obstruction. The uniqueness of ThuLEP as a concept made it a blueprint for other laser and nonlaser enucleating techniques based on the emphasis on two principles: widely blunt anatomical dissection and demystification of energy sources as being secondary for transurethral enucleation. The original technique has been technically refined by the inventor and other working groups in the field. The evolutionary modifications followed the academic discourse on anatomical enucleation for measures to prevent early postoperative stress urinary incontinence and preservation of antegrade ejaculation. Variations of the original three‐lobe dissection technique were introduced with two‐lobe approach or en bloc dissection. The manuscript is accompanied by an instructional video and surgical atlas on the currently most commonly applied two‐lobe technique.

scientific reception away from highlighting the impact of a single energy source (back) to the overarching principle of the common ground of enucleating techniques: anatomical enucleation (AEEP), what began with the publication of Yasunori Hiraoka and monopolar transurethral detachment prostatectomy technique (TUE) in 1983 (Hiraoka, 1983) in Japanese and 1989 in English (Hiraoka & Akimoto, 1989).

| Historical context of Thulium:YAG-based enucleating technologies
But, the honour for the historical achievement of exposing transurethral enucleation to a broader readership and surgical peers is due to Peter Gilling and Mark Fraundorfer for their work and publication on 'Holmium:YAG laser enucleation of the prostate combined with mechanical morcellation: preliminary results' in 1998 (Fraundorfer & Gilling, 1998). In the wake of HoLEP, transurethral plasmakinetic (i.e. bipolar) enucleation of the prostate (PkEP) followed in 2006 (Neill et al., 2006). In the second half of the 2000s, all other transurethral laser-based enucleation techniques led by Tm:YAG vapo-enucleation (ThuVEP) (Bach, Wendt-Nordahl, Michel, Herrmann, & Gross, 2009) and transurethral anatomical enucleation with Tm:YAG support (ThuLEP) , later diode laser enucleation of the prostate (DiLEP) (Lusuardi et al., 2015) and finally Lithium-Borate 'Greenlight' enucleation of the prostate (GreenLEP) (Gomez Sancha et al., 2015) entered the endourological stage to finally replace open prostatectomy (OP) and TURP.

| The concept of transurethral anatomical prostatectomy with Tm:YAG laser support (ThuLEP)
There is a plethora of acronyms today claiming to stand for 'ThuLEP'. However, some rather represent approaches to vapoenucleate (Iacono et al., 2012) or vapo-resect the prostate (Yang, Liu, & Wang, 2016). The header of original description of the technique published in 2010 outlined the fundamental principle of the concept: 'transurethral anatomical prostatectomy with laser support' . The novelty of this approach was neither transurethral enucleation nor marketing of the new Tm:YAG laser.
The novelty laid in the focus on blunt mechanical anatomical dissection of the whole transitional zone using the laser energy solely for incising of the mucosa, dividing the adenoma into three lobes and cutting of adhesions or ingrowing centripetal vessels. The principle of thulium-assisted transurethral anatomical enucleation was first demonstrated at a laser meeting at Kairo University in 2009 and triggered one of the finest teacher of HoLEP, the late Mostafa El Hilali, to comment with the words 'I did not know that you could do it […anatomical dissection…] with Thulium […YAG…]' (Herrmann, 2009). This comment shed light on two aspects: firstly, even the most academic promoters of HoLEP at that time where overestimating the impact of 'their' laser, Holmium:YAG (Ho:YAG), in the course of transurethral enucleation of the prostate. At this point of time, it was 'common sense' that it was only possible to find or access the correct anatomical plane with a pulsed laser. The spiritedly fought controversy since the advent of Tm:YAG laser was about whether other, in this case Thulium:YAG lasers, could have the potential to 'enucleate', although continuous wave lasers were vaporising/ vapo-incising lasers in the contrary to the mechanically disrupting Holmium lasers. It culminated when Thulium vapo-enucleation (ThuVEP) was introduced in 2008 . The demonstration of this novel transurethral technique showed a straightforward transurethral vapo-incising enucleating technique that overcame the obstacles of a rather time-consuming vaporesection technique using the initial 70 Watts generator (Xia, 2009). The vapo-incisions into the prostate to cut out the sample incorporating the transitional zone were aiming at the level of the surgical capsule, thereby emulating the template of conventional HoLEP (Fraundorfer & Gilling, 1998). The orientation in the procedures and the extend of the template based on the surgical experience of the presenting surgeons and was not anatomical in the today-accepted context. However, the major criticism of this technique was that the sealed and caramelised surface of the incisions were violating the viewing habits of the 'HoLEP community' (HoLEPcentrism, Gilling & Williams, 2008) and clearly did not match the 'cotton wool landmarks' of the surgical plane, or at least what was considered to be 'the anatomical capsule' at that time (El-Hakim & Elhilali, 2002;Kuo et al., 2003). Today, it is accepted that both HoLEP and ThuVEP techniques both alter the capsule either with boiling by the vapour bubble ('white') or caramelising in the vapoincision 'brown'. Out of the personal struggle of the author of this article to reproduce the incising 'ThuVEP' template with Tm:YAG, ThuLEP was born. Due to the blunt dissection, the surface of the peripheral zone aka surgical capsule remained unaltered and orientation was easily maintained throughout the procedure.
The first video publication of ThuLEP in three-lobe technique at the World Congress of Endourology 2009 in Munich was the end point of the discussion whether 'Thulium could' and 'only Holmium can' find the surgical plane (Imkamp, 2009). It was the starting point of a discussion on what is commonly accepted as anatomical endoscopic enucleation of the prostate 'AEEP', today. Therefore, the surgical twins 'ThuVEP' and 'ThuLEP' demonstrated the whole spectrum of laser action in enucleating techniques: ThuVEP focusing vaporising features during enucleation and ThuLEP focusing on almost blunt detachment and laser assistance. The principle of the latter on anatomy-focusing approach was mimicked by other continuous wave lasers (LBO/ 'Greenlight' and 980nn diode laser) that had not been found suitable for enucleation at the initial point of the discussion (Gomez Sancha et al., 2015;Lusuardi et al., 2015). Today, the energy source seems to be secondary for the success of EEP and rather a result of institutional resources or personal preferences of a skilled surgeon (Elshal et al., 2015), as transurethral endoscopic enucleations have a same effect given they are anatomical EEP (Herrmann, 2016a; Hiraoka, 2017).

| Surgical and anatomical considerations
In principal, all enucleating techniques can be broken down to two principles. 'True' anatomical enucleation by mainly blunt dissection and thereby developing the surgical plane leaving the surface intact for visualisation and orientation and on the other side vapoenucleation using the vaporising capacity of the energy source to cut and seal the surface at the same time. In vapo-enucleation technique, a high level of experience gains momentum. The cutting plane aims to reach the anatomical plane of the interphase to the peripheral zone. At best, these planes are identical (Figure 1, Kyriazis et al., 2015), but a chance of extra-anatomical preparation with incomplete resection or excess of resection template with the chance of perforation of the capsule is possible (Elshal et al., 2016;Iacono et al., 2012).
The transition from 'anatomical' to 'extra-anatomical' is fluent ( Figure 2). In experienced surgeons, the two approaches are mixed within the procedure depending on speed and anatomical features of the gland. The authors of this publication advocate start with anatomical preparation before moving to 'vapo-enucleation' (Herrmann, 2017). Lately, also promoters of vapo-enucleation embraced the anatomical ThuLEP approach for comparative studies of enucleating techniques (Becker, Herrmann, Gross, & Netsch, 2018;Gross, 2019).
A surrogate parameter for 'complete resection' is the PSA drop, postoperatively. Given the mainstay of enucleating techniques in total prostate volume larger than 80ml, PSA drop is expected to be around 80% in the absence of concomitant prostate cancer (Gross, Orywal, Becker, & Netsch, 2017;Herrmann, 2016b;Tinmouth et al., 2005).

| SURG I C AL RE SULTS
The vast amount of data from randomised controlled studies with long-term follow-up longer than 4 years is not available for ThuLEP however, in RCTs ThuLEP versus TURP (Swiniarski et al., 2012) and ThuLEP versus bipolar EEP (Feng, Zhang, Tian, & Song, 2016). ThuLEP demonstrated favourable higher intra-operative safety with regard to haemostatic properties. Applications for Thulium vapo-enucleation (ThuVEP) with the same energy source demonstrated long-term result for complication rates in the range of HoLEP (Cornu et al., 2015) and bipolar enucleation (Li et al., 2015;Lin et al., 2015). No urethral and bladder neck strictures in a RCT ThuLEP with HoLEP were reported during the 18-month follow-up period (Zhang, Shao, Herrmann, Tian, & Zhang, 2012).
In addition, ThuLEP seemed to be safer with regard to the development of bladder neck strictures when compared in a RCT with Thulium Vaporesection (ThuVARP, TmLRP-TT, Table 1) (Sun et al., 2019). Two additional studies on ThuLEP versus HoLEP came to the same conclusion that no clinically significant difference could be substantiated in comparison with HolEP in 6 (Becker et al., 2018)-, or 12-and 18-month follow-up (Zhang et al., 2019). The largest study so far on Thulium:YAG laser in ThuVEP technique (Zhang et al., 2019) with 60-month follow-up reported long-term durability of voiding improvements and overall re-operation rates of 2.4% (Gross, Netsch, Knipper, Holzel, & Bach, 2013;Gross et al., 2017). More studies of randomised controlled trials with longterm follow-up would be ideal to rest the case. However, this topic will become more complicated with the advent of novel Tm fibre lasers that work for both urolithiasis and soft tissue. These lasers have the potential to take over a larger share of new laser devices in clinics in the future. The difference is more or less academical, but sophistically would call for individual evaluation (Becker et al., 2019;Tiburtius, Gross, & Netsch, 2015  .

F I G U R E 1
Anatomical and extraanatomical enucleation (Kyriazis et al., 2015) F I G U R E 2 Gradual modification of enucleating techniques. From blunt anatomical to vapo-enucleation (Herrmann, 2017)

| Modification of transurethral anatomical enucleation of the prostate with Tm:YAG support
The original concept of ThuLEP as 'transurethral anatomical prostatectomy with laser support' was developed in 2009 and published in 2010 . Shortly after that, ThuLEP in two-lobe technique and en bloc enucleation were explored and demonstrated in 2012 (Endoskills, Fortbildungen der Akademie der Deutschen Urologen, 2012). The principle of widely blunt mechanical anatomical dissection of the whole transitional zone using the laser energy solely for incising of the mucosa, dividing the adenoma into three lobes and cutting of adhesions or ingrowing centripetal vessels is present in all variations of ThuLEP. The basic difference between 3 lobe, 2 lobe (Baazeem, Elmansy, & Elhilali, 2010;Dusing et al., 2010;Wolters, Huusmann, Oelke, Kuczyk, & Herrmann, 2016a, 2016b and en bloc enucleation (Kim, Lee, Kwon, Cho, & Kim, 2015) is the incision into the mucosa ventrally ('double Ω/ U', 'three horseshoe' (Miernik & Schoeb, 2019) and the incision of the mucosa to dissect the transitional zone in 3 lobe (3), two lobe (2)   . However, other authors investigated traditional three-lobe HoLEP versus HoLEP en bloc, concluding that en bloc resulted in reduction of total operative time. They supposed that the reason for this result was the easier identification of the surgical capsule in en bloc approach (Rapoport et al., 2018).
From the inventors' vast experience in all variations of ThuLEP, the proposed advantage of either one over the other approach is rather subjective. Clear 'limitations' of three-lobe technique for example with regard to the applicability for anatomical preparation are unproven and may be related to individual challenges of preparation technique (Pacchetti et al., 2019;Saredi et al., 2017). Clearly, starting with the lateral lobe allows for easier blunt exposure of the surgical capsule than starting with the median lobe. Therefore, the differences or advantages of two lobe or en bloc derive when compared to original three-lobe technique derive rather from the fact that the 'first lobe' is a lateral lobe than the fact that it is 'not three lobe'.  (Herrmann, 2016) The introduction of the mechanical tissue morcellator (Fraundorfer & Gilling, 1998) did not change the basic principle of the enucleating technique but added a tool to facilitate and potentially speed up the evacuation of the dissected tissue. However, the downside is that mechanical morcellation adds a further learning curve to the whole process of adapting AEEP in daily practice (Bae, Oh, & Paick, 2010).
For exit strategy the adoption of 'mushroom' technique (Hochreiter, Thalmann, Burkhard, & Studer, 2002)  However, precautions must be taken for a reliable turnover of irrigation fluid in order to avoid heat built-up in the surgical field.

| ThuLEP in two-lobe technique. Description of technique and surgical atlas accompanied by instruction video
The five major surgical steps of the ThuLEP procedure in two-lobe technique are: • Ω-like (Omega) incision with a distance of 5 mm to the  (Martini, 2009), which leads to a potential deficit in fibrinogen availability and therefore coagulation disorders. Karl Storz GmbH) is advised to keep as backup for coagulation not only in the learning curve but also in case of opening of a periprostatic sinus, which needs pressure coagulation to seal the vessel.

| Use of laser power of Tm:YAG
Vaporisation/ Incision: The vaporising features of laser energy is used to vapo-incise the mucosa, coagulate centripetally ingrowing vessels at low power energy from 5 to 10 Watts or defocusing, and to purge the plane as for example in the fibro-anterior stromal region in high power setting 90 W. To avoid switching of the energy level, repeatedly the use of a double pedal for Incision or coagulation is recommended.

| Incision around the verumontanumejaculation preservation
At first, an Ω-like (Omega) incision around the verumontanum is carried out. The incision starts with a horizontal incision proximal to the verumontanum followed by an incision of the mucosa laterally on the left and on the right lobe until the distal third of the verumontanum. In ejaculation sparing approaches, a strip of 1 cm on each side of the verumontanum has to be preserved. If the space next to the verumontanum is too narrow or the apical adenoma is too bulky, the Ω-like (Omega) incision is extended 5 mm up from the base of the paracollicular grooves onto the mucosa of the lower part of the side lobe in order to create an untouched plane of mucosa around the verumontanum for ejaculatory hood preservation (Figure 3a,b) as an extended ejaculatory hood template (Wolters et al., 2016) when compared to the 'original' ejaculatory hood template of Kim, Song, Ku, Kim, and Paick (2015). In principal, all intended ejaculatory function preserving techniques are based on the findings of Dorschner and Stolzenburg (1994). All attempts need to respect the integrity of the M. ejaculatorious sling in order to allow for pulling down of the verumontanum below the sphincter for ejaculation of semen into the bulbar urethra. Therefore, as the apical portion of the transitional zone is rather 'untouched' in the novel extra-anatomical ablative or nonablative MIS antegrade ejaculation rates are gradually higher up to more than 90%. The rate of antegrade ejaculation widely corresponds to the amount of tissue ablated. The highest rate could be achieved in both arms of Water Study above 90% when the volume ablation was at 25% (Kasivisvanathan & Hussain, 2018) and was similarly high in both arms in GOLIATH Study of LOB (Greenlight) versus TURP (PSA reduction 58%) .

| Exposure of the surgical capsule
The cranial end of the mucosal Ω-incision into the lateral lobe is extended anteriorly, also referred to as the hockey-stick incision  (Fraundorfer & Gilling, 1998) or 'curtain opening incision' (Kim, Lee, & Oh, 2013). This incision prevents tearing of the mucosa caudally into the sphincteral region and additionally reduces the tearing effect on the caudal mucosa inside the sphincteral region (Dorschner & Stolzenburg, 1994).

| Enucleation of the left lobe
Now, the resectoscope is guided into the space between transitional and peripheral zone and the adenoma is loosened circumferentially with the beak of the resectoscope (Figure 3e,f). If the plane is followed thoroughly, the surgical plane can be followed until 12°.

The verumontanum was a very important landmark in traditional
HoLEP technique, as the 12° incision was cut down into the mucosa ventrodorsally for the lateral lobe (El-Hakim & Elhilali, 2002;Fraundorfer & Gilling, 1998;Kuo et al., 2003). However, in anatomi- (ESUI). The principle of anterior-posterior dissection has been of fundamental importance in Nesbit (Nesbit, 1943) and all contemporary enucleation resection techniques like proposed by Liu et al. (2010). In addition, this approach has been reported to reduce ESUI after AEEP (Endo et al., 2010). However, the learning curve itself has been described as fundamental for the rate of ESUI (Shah et al., 2007). It is striking to see that this concern was already heeded in the 1st publication of EEP in 1983 by Hiraoka (2017).
To loosen the lobe, the tissue first has to be detached apically Adhesions are cut with laser energy, small vessels sealed with low energy mode (Figure 4c,d). Thereby excellent vision is maintained.
The lobe is detached until the bladder neck and finally pushed into the bladder.

| Combined enucleation of the median and right lobe
The median lobe and the right lobe are enucleated en bloc. The resectoscope is placed at the 7 o'clock position next to the dissected edge in a steep angle as on the left side at the beginning of the procedure. The median lobe is lifted with the shaft rolled over to the right side (Figure 4e).
Starting with blunt dissection with the resectoscopes sheath, the right lobe is loosened circumferentially from 7 o'clock to 12 o'clock position.
The remaining mucosal band is cut like on the left side from peripheral towards the midline (Figure 4f). Finally, the detached median lobe and right lobe are pushed into the bladder (Figure 4g,h).

| Removal of prostatic tissue by mechanical morcellation
Once all lobes of the adenoma are deposited into the bladder, haemostasis is either ensured using coagulation of the mucosal edges at the bladder neck in low power setting at 5-10 W or defocused laser in 90 W setting in order to improve visualisation during morcellation or planar bipolar coagulation can be performed using either a resection or vaporisation probe in order to safe surgical theatre time.
Irrigation outflow is stopped. The angled 25-cm-long telescope (6° line of vision) is introduced into the working sheath with an adaptor in such a way that the pressure in the bladder does not significantly drop in order to avoid bleeding. In between, the irrigation bags are positioned at a maximum of 80 cm above bladder level in order not to overdistend the detrusor. A second irrigation system is connected to an angled 25-cm-long telescope (6° line of vision). The morcellator blade is introduced in such a way that the pressure in the bladder does not drop significantly to prevent bleeding from venous vessels at low bladder pressure.
The blade consists of a 5-mm-outer sheath and a rotating inner shearing knife that cuts the suctioned tissue off against the outer sheath. It is inserted through the central channel of the telescope.
Rotation speed of the morcellator is adopted to tissue hardness.

| E XIT S TR ATEGY
The surgical procedure ends with a final inspection of the resection cavity after removal of the morcelloscope and reinsertion of the working element into the resectoscope sheath. The collapsed bladder now exposes the boundary to the bladder neck mucosa entirely. The fossa is thereby closed and can collapse, and residual bleeding will result in a tamponade of the fossa. At the end, the balloon is fixed to the fossa using a knotted compress (tie). This does not serve for traction purposes but for closing off the fossa. Regularly, the catheter can be removed on the first postoperative day.