Abstract
Extensive research has been conducted in search of factors that can predict the likelihood of successful testicular sperm retrieval in nonobstructive azoospermia patients. Clinical factors such as patient age, testicular volume, presence of varicocele, cryptorchidism, and Klinefelter syndrome; laboratory factors such as serum FSH level, inhibin B level, and presence of genetic disturbances; and the histopathologic pattern of testicular tissue have all been investigated in the literature. Of all the above-mentioned factors, the histopathologic pattern appears to be most influential in predicting surgical sperm retrieval outcome.
9.1 Introduction
The introduction of surgical sperm retrieval in the 1990s has revolutionized the field of male infertility, notably as it provided hope to patients with azoospermia to father their biological children. Since that time, efforts have focused on optimizing the sperm retrieval techniques and searching for predictors of success.
Azoospermia, defined by the absence of sperm in the ejaculate after examination of the centrifuged pellet, occurs in around 1 percent of men of the general population and in up to 12 percent of infertile men [1,2]. Azoospermia can be classified as obstructive or nonobstructive, with nonobstructive azoospermia (NOA) accounting for most cases (60 percent) [1,2]. This can be caused by a wide spectrum of etiologies, some which are severe and untreatable, such as genetic (Klinefelter syndrome and Y chromosome microdeletions), congenital (cryptorchidism), exposure to gonadal toxin (chemotherapy, radiotherapy), post-infection (mumps), trauma, and idiopathic; in some rare occasions NOA can be due to a treatable endocrine disorder such as hypogonadotropic hypogonadism, which is simply testicular failure due to absence of gonadotropin stimulation. Therefore, a detailed history and proper physical exam should be conducted for all azoospermic patients to identify the type and possible etiology for the azoospermia [3].
Several sperm retrieval techniques for NOA patients have been described. Devroey et al. were the first to perform conventional testicular sperm extraction (cTESE) for a group of men with NOA, proving that sperm could be retrieved from patients with testicular failure [3]. Craft and Tsirigotis introduced a simpler and less invasive modality for sperm retrieval, namely testicular sperm aspiration (TESA) [4]. Nonetheless, the surgical sperm retrieval rate (SRR) with these two modalities did not exceed 50 percent. Aiming to improve the SRR and, at the same time, minimize damage to testicular parenchyma, Schlegel introduced the microsurgical testicular sperm extraction (micro-TESE) technique. This method, which utilizes surgical magnification, allows accurate dissection and sampling of dilated seminiferous tubules, thus avoiding vascular damage or extensive destruction of testicular tissue. While micro-TESE can be considered the gold standard method for sperm retrieval in cases of NOA, its success rates are quite variable, ranging from 35 to 77 percent. This discrepancy in success rates can be a subject of considerable uncertainty to the couple seeking treatment [5–8].
There is no doubt that couples presenting with azoospermia face a considerable burden physically, emotionally, and financially in the process of conceiving a child. Understanding the predictors of successful sperm retrieval would provide crucial information necessary for optimal patient counseling that would allow the couple to choose the best method of treatment for their particular condition.
This chapter aims to review the most important predictors of surgical sperm retrieval for men with NOA. Many factors have been investigated and can be classified for simplicity into clinical, laboratory, and histopathological factors.
9.2 Clinical Evaluation
The etiology of infertility carries important prognostic information, whether it is a genetic cause like Klinefelter syndrome or Y chromosome microdeletions, or an acquired one like cryptorchidism, post-cancer treatment, or varicocele [9]. Other clinical factors, such as patient age and testicular size, can also have an impact on the SRR (Table 9.1).
Table 9.1 Predictors of testicular sperm retrieval
| Predictor | Effectiveness | Ref. |
|---|---|---|
| Klinefelter syndrome | The SRR in patients with Klinefelter syndrome is 30–50 percent Higher pre-retrieval serum testosterone seems to have a favorable effect on the SRR | [10–14] |
| Cryptorchidism | The SRR for cryptorchid men is believed to be higher than all other men with NOA, with success rates reaching 74 percent. | [13,14] |
| Varicocele | Varicocele ligation in NOA patients with clinical varicocele has a favorable effect on SRR | [15] |
| Age | Controversy surrounds the predictive value of patients’ age on the sperm retrieval outcome | [16–22] |
| Testicular volume | Testicular volume has a low or no predictive value for SRR | [23,24] |
| FSH | FSH has a low-moderate prognostic value for SRR with better results obtained with lower serum FSH values | [25–27] |
| Inhibin B | Controversy surrounds the predictive value of serum inhibin B levels on the sperm retrieval outcome | [28–31] |
| Y chromosome microdeletion | The result of Y chromosome microdeletion significantly predicts the sperm retrieval outcome. Patients with AZFc and partial AZFb microdeletions have an SRR of 54.8 percent and 7.1 percent, respectively. AZFa, AZFb, or AZFa/b microdeletions are associated with the worst prognosis and are deemed likely for failure | [32,33] |
| Surgical technique | The highest SRR is achieved with mTESE, followed by TESE and TESA | [34–36] |
| Histologic pattern | Hypospermatogenesis carries the best SRR (80–100 percent), followed by maturation arrest (40–80 percent) and Sertoli-cell-only syndrome (4–51 percent) | [37–40] |
| Medical treatment prior to surgical sperm retrieval | Testicular hyperstimulation with medications such as clomiphene citrate, human chorionic gonadotropin, follicular FSH, or aromatase inhibitors may have a positive effect on the SRR, although with conflicting results. | [41–45] |
9.2.1 Klinefelter Syndrome
Klinefelter syndrome (KS) is the most commonly encountered genetic abnormality in men with infertility. It is characterized by the presence of a supernumerary X chromosome (47,XXY), which presents in mosaic forms (e.g., 46,XY/47,XXY) that constitutes around 10–15 percent of KS patients or non-mosaic forms (e.g., 47,XXY) that constitutes around 80–90 percent of KS patients [46–48], and to a lesser extent in the form of chromosomal aneuploidies with more than one extra X chromosomes (e.g., 48,XXXY or 48,XXYY) and structurally abnormal X chromosome due to translocation (e.g., 47,iXqY) [49–52].
Klinefelter syndrome is prevalent in around 3–4 percent of infertile couples and in 10 percent of azoospermic patients [53]. It was once believed that KS patients are sterile, and the only way to father children was through adoption or donor insemination, until further reports starting from the 1980s showed sperm in some cohorts of KS patients, demonstrating the possible presence of spermatogenic foci in their testicles [53,54]. Around 92 percent of non-mosaic KS patients do not produce sperm in their ejaculates [51], while mosaic forms may present with a picture of oligospermia and hence have a less severe form of infertility.
Up to 50 percent of men with KS can have sperm detected during sperm retrieval using TESE/micro-TESE [10]. Others have reported a lower SRR; Garolla et al. evaluated 111 non-mosaic azoospermic KS patients retrospectively and reported a 34 percent SRR [11]. Despite that, the SSR in KS patients is believed by some authors to be equivalent to or slightly less than the SRR for men with NOA secondary to other causes [12].
Predictive factors for sperm retrieval in KS patients have been a debatable issue for some time, with no real consensus available to draw solid conclusions. Many factors have been investigated, such as age, testes volume, serum levels of testosterone, luteinizing hormone (LH), and presence of mosaicism, without any clear recommendation [55–57].
Patients younger than 30–35 years old are believed to have a better chance for sperm retrieval compared to older men [55–57]. This has been explained by the progressive testicular degeneration that occurs as KS patients age. On the contrary, other authors did not find any difference in retrieval rate between young and older patients with KS [58,59].
Another factor is the serum testosterone level before surgical sperm retrieval. Sabbaghian et al. observed that higher testosterone levels were associated with better SRR using micro-TESE in KS patients. The authors explained that KS patients presenting with testicular failure usually have hyperplastic Leydig cells, which are unable to produce enough testosterone. Since intratesticular testosterone is vital for normal spermatogenesis, the authors suggested that a serum level testosterone above 2.95 ng/ml may indicate the presence of focal areas of sperm production [60].
Ramasamy et al. reported improved SRR in KS patients who received gonadotropin therapy, suggesting that exogenous gonadotropins decrease the endogenous levels, thus causing a reset-like mechanism for the hormonal receptors in the testicular Sertoli and Leydig cells, leading to later improved function [61]. Another retrospective study by Ramasamy et al. investigating the effects of medical therapy on the sperm retrieval outcomes in KS patients found that men with low baseline testosterone levels receiving treatment before sperm retrieval had a significantly higher SRR when their testosterone levels post-medical therapy were improved above 250 ng/dl compared to men who did not. The authors suggested that a better response to medical therapy may predict the sperm retrieval outcome in KS patients [62].
9.2.2 Cryptorchidism
Cryptorchidism is a common childhood malformation occurring in 3 percent of full-term infants and to a greater extent in preterm infants. It is associated with infertility, hernia, testicular torsion, and tumors. Controversy is still present on whether the age of correction and testes volume is considered as a combined predictor for sperm retrieval [63]. In general, the SRR for cryptorchid men is believed to be higher than for all other men with NOA, with success rates reaching 74 percent [13,14].
Raman and Schlegel investigated 38 cryptorchid patients out of 275 NOA patients and observed significantly higher SRR in patients who had their orchiopexy performed before the age of 10 years compared to a later age of correction [14]. Wiser et al. found no significance with regards to the age of orchiopexy in a group of 40 patients [64]. This latter finding was also echoed by Glina et al. [65].
9.2.3 Varicocele
Varicocele is the most common correctable cause of male infertility, prevalent in about 25–35 percent of infertile men and 5 percent of men with NOA [66,67].
The outcome of varicocelectomy on azoospermic patients was investigated by Mattews et al., who observed that sperm could become detectable in the ejaculate of azoospermic patients following varicocelectomy, thereby avoiding testicular sperm retrieval at the time of intracytoplasmic sperm injection (ICSI). Even in patients who remain azoospermic, varicocelectomy was found to improve the SRR at the time of ICSI [68].
Inci et al. evaluated 96 patients with varicocele and NOA. These authors compared the surgical sperm retrieval outcomes in two groups of patients: 66 patients who underwent varicocelectomy 5–6 months prior to ICSI; and 30 patients who went directly to ICSI. The results showed a statistically significant improvement in the SRR in the group who underwent varicocelectomy compared to the untreated group. It is worth mentioning, however, that there were no significant differences in embryo quality, abortion rate, or live birth rate between the groups [69].
Others did not show a significant improvement in the success rates of sperm retrieval by micro-TESE following varicocelectomy in NOA patients with varicocele. Schlegel et al. examined 31 NOA patients who underwent varicocelectomy and showed that sperm appeared in the ejaculate of 22 percent of patients in at least one semen analysis following surgery, while only 9.6 percent of them produced viable sperm at the time of ICSI [70]. In this study, however, the authors included men with clinical as well as subclinical varicocele.
A systematic review and meta-analysis by Esteves et al. examined 18 studies, including 468 patients with NOA and clinical varicocele. The authors reported a 2.6-fold increase in SRR in treated versus untreated groups, with 44 percent of patients having enough viable sperm in their ejaculate to avoid testicular sperm retrieval [15].
9.2.4 Age
Advancing age is believed to be a negative predictor for pregnancy rates in general, and surgical sperm recovery rates specifically. Younger patients undergoing surgical sperm retrieval tend to have better results with ICSI than do older patients [16–18]. The explanation for this is that as men age, the testicular areas of spermatogenesis decrease, in concordance with a reduction in testes size and seminiferous tubule length [19,20]. Despite this, some studies failed to confirm these observations, thus making age a debatable predictive factor for sperm retrieval.
Ramasamy et al. did not observe any adverse effects for age on sperm retrieval. The authors highlighted that most older patients had acquired causes of NOA, whereas the causes were predominately congenital in the younger age group [21]. Similarly, Enatsu et al., in a study of 329 men with NOA undergoing surgical sperm retrieval and ICSI, did not find a significant adverse effect of patient age on SRR [22].
9.2.5 Testicular Volume
It is generally believed that testicular size reflects the state of spermatogenesis, suggesting that smaller testes may predict worse histopathology and hence lower SRR, while larger testes may have a better SRR [71–73].
As such, some authors tried to identify cut-off values for the testicular size that would predict surgical sperm retrieval. Macaroni et al. reported a 30 percent SRR with micro-TESE when the testes size was less than 8 ml [74] , whereas Bromage et al. reported a 29 percent SRR with TESE when the testes size was less than 4 ml [75]. Ziaee et al. reported that a positive SRR can be expected in patients with an average testes size of 17.5 ml, while a negative SRR will be obtained with an average testes size of 5.7 ml, with a positive predictive value of 80 percent and a negative predictive value of 96.9 percent with regards to testicular volume and successful SRR (area under the curve [AUC] = 0.95) [76]. However, the authors used different surgical sperm retrieval methods, thereby suggesting improbability of their results. On the other hand, considerable evidence has failed to confirm a significant effect of testicular size on SRR.
A meta-analysis by Hao et al. including five studies with a total of 1764 patients with NOA undergoing surgical sperm retrieval reported that testicular volume had a low predictive value for SRR. The pooled odds ratio was 1.98 (95 percent CI: 1.11–3.53), with sensitivity of 0.8 (95 percent CI: 0.78–0.83), specificity of 0.35 (95 percent CI: 0.32–0.39), positive likelihood ratio of 1.49 (95 percent CI: 0.94–2.36), and negative likelihood ratio of 0.73 (95 percent CI: 0.60–0.88) (AUC = 0.638) [23].
Bryson et al. conducted a retrospective review of 1127 NOA patients who underwent micro-TESE followed by ICSI. The authors divided patients into three groups according to testes size: group 1: testis size <2 ml; group 2: testis size 2–10 ml; group 3, testis size ≥10 ml. The SRR rate was similar among the three groups: group 1, 54.7 percent; group 2, 56.2 percent; and group 3, 55.1 percent. Moreover, no significant differences were observed with regards to pregnancy rates or live births between patients from the three groups who had a positive sperm retrieval outcome [24].
9.3 Laboratory Predictors
Laboratory predictors of SRR have been based on tests that evaluate the function of the hypothalamic–pituitary–gonadal axis, such as FSH, testosterone, anti-Müllerian hormone (AMH), inhibin, and the genetic detection of chromosomal abnormalities such as KS, chromosomal translocations, and Y chromosome microdeletions.
9.3.1 Follicle-Stimulating Hormone
Spermatogenesis is a complex process that is intricately orchestrated by the proper functioning of the hypothalamic–pituitary–gonadal system. Follicle-stimulating hormone is a pituitary glycoprotein produced in response to gonadotropin-releasing hormone stimulation from the hypothalamus. It produces its action by binding to the testicular Sertoli cells, stimulating them to secrete inhibin B, activin, and other nutrients essential for spermatogenesis. Follicle-stimulating hormone is one of the important hormones that is considered as a predictor for testicular function and, therefore, a predictor for sperm retrieval. While it is believed that, in general, FSH concentration is inversely related to SRR, no agreed-upon cut-off value can guarantee the finding of sperm during sperm retrieval [41,77,78].
Ramasamy et al. evaluated the sperm retrieval outcomes of 792 patients undergoing micro-TESE. The pre-procedure FSH levels were divided into four groups: group 1, <15 IU/ml; group 2, 15–30 IU/ml; group 3, 31–45 IU/ml; and group 4, >45 IU/ml. The authors reported a statistically significantly higher SRR in groups 2 (60 percent), 3 (67 percent), and 4 (60 percent) in comparison to group 1 (51 percent) [25]. By contrast, Chen et al. identified an FSH value of 19.4 IU/ml above which no sperm recovery could be expected on retrieval procedures [26].
A systematic review and meta-analysis by Yang et al., including 11 studies and 1350 patients, was conducted to examine the predictive value of FSH on a positive SRR. The authors found FSH to have a moderate diagnostic value as an independent predictor for SRR in patients with NOA (pooled diagnostic odds ratio 3.99 [95 percent CI: 2.33–6.83] and an AUC of 0.72 ± 0.04) . The authors, however, observed significant heterogeneity that was mainly influenced by the region of the included studies and the age of the patients. The diagnostic odds ratio was four times higher in studies from East Asia compared with other regions, and also four times higher in patients younger than 33 years in comparison to older patients [27].
9.3.2 Inhibin B
Inhibin B, along with other glycoproteins such as activins and anti-Müllerian hormone, is considered negative feedback regulators of the hypothalamic–pituitary–gonadal axis. Inhibin B levels decrease in cases of testes dysfunction and hypospermatogenesis. These hormones have been measured in both blood plasma and semen, and assessed as predictors of sperm recovery in patients with NOA [79].
Some reports strongly advocate its role as a predictor of sperm retrieval with a sensitivity and specificity reaching above 80 percent [28,29]. However, most published data do not consider inhibin B as a predictive factor at all. One study by Tunc et al. investigating 52 NOA patients showed no significant differences in SRR based on serum inhibin levels [30]. Another study, by Vernaeve et al., showed the same findings from 185 patients with NOA undergoing sperm retrieval. The authors measured serum inhibin B before the procedure and divided the patients into groups according to whether sperm was recovered or not. The mean serum inhibin was 37.3 ± 5.4 pg/ml in the group of patients in whom sperm was recovered, and 44.9 ± 7.7 pg/ml in the counterpart with failed retrieval. The authors concluded that inhibin B, alone or combined with FSH, is of limited predictive value in sperm recovery in NOA patients [31].
Mitchell et al., in a study comparing the SRR in 139 azoospermic patients, found that seminal levels of inhibin or AMH did not influence the retrieval outcome [80].
9.3.3 Y Chromosome Microdeletion
Y chromosome microdeletions were first described by Tiepolo and Zuffradi, and are recognized as significant causes of spermatogenic dysfunction and male infertility. These deletions are localized to a group of genes located in the heterochromatic and adjacent euchromatic regions of the Y chromosome, which is also known as the Azoospermia Factor (AZF). Three non-overlapping regions of the Y chromosome, termed AZFa, AZFb, and AZFc, significantly contribute to spermatogenesis; microdeletions within these regions would lead to primary testicular insufficiency characterized by azoospermia or severe oligozoospermia.
AZFa microdeletions carry the worst fertility prognosis as they are associated with Sertoli-cell-only syndrome (SCOS), while AZFb deletions are usually associated with maturation arrest [81,82]. Testing for Y chromosome microdeletions is crucial in azoospermic patients before sperm retrieval as the test result carries prognostic information. AZFa, AZFb, or AZFa/b microdeletions are associated with the worst prognosis and are deemed likely for failure. Patients with AZFc and partial AZFb (associated or not with AZFc) microdeletions have a surgical SRR of 54.8 percent and 7.1 percent, respectively. Moreover, AZFc patients are not necessarily azoospermic and may be candidates for ICSI using sperm from their ejaculate [32,33].
9.3.4 Surgical Technique
Various methods for surgical sperm retrieval have been identified; namely percutaneous TESA, cTESE, and micro-TESE. Each method has its pros and cons, and are described in detail in Chapter 6 [83].
Micro-TESE is considered superior to other methods as it allows a magnified visualization of the seminiferous tubules, allowing selective identification and selection of dilated opaque tubules suspected of containing sperm [34,35].
Many systematic reviews and meta-analyses have been published discussing and comparing the different SRR between methods of surgical sperm retrieval. Deruyver et al., in a systematic review that included seven studies comparing cTESE and micro-TESE, reported an overall SRR ranging between 16.7 and 45 percent in the conventional arm compared to 42.9–63 percent in the microdissection arm. One point noted in this review is that SRR with micro-TESE was significantly higher in Sertoli-cell-only cases of NOA, suggesting that focal areas of spermatogenesis identified microscopically aided in these results. In cases of maturation arrest or hypospermatogensis, the micro-TESE outcome was less advantageous [84].
Another meta-analysis and systematic review by Bernie et al. included 15 studies comparing the three methods of retrieval: TESA, cTESE, and micro-TESE. Data from 1890 patients was analyzed, showing superiority for micro-TESE regarding the SRR (52 percent) in direct comparison to cTESE (35 percent), equating to 1.5 times higher likelihood of sperm retrieval with micro-TESE than cTESE. On the other hand, sperm were twice as likely to be retrieved with cTESE (56 percent) when compared to TESA (28 percent) [36].
9.3.5 Histological Pattern
Testicular histology is believed to be the single most significant predictive factor for successful sperm recovery. Nonetheless, in order to obtain such information, a diagnostic testicular biopsy is required. This practice has not been endorsed by international societies as the biopsy may have a negative influence on testicular function and hence might alter the outcome of the subsequent sperm retrieval. Furthermore, the diagnostic biopsy does not provide an overall view of the histopathologic pattern, which is often variable in the majority of cases. It is believed that hypospermatogenesis carries the best SRR (80–100 percent), followed by maturation arrest (40–80 percent); SCOS has the worst SRR, as low as 4 percent in some studies and as high as 51 percent in others [37–40].
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