The size of the contralateral testis has been used by many authors in predicting the condition of its contralateral nonpalpable counterpart [5, 8]. Testicular hypertrophy in cases of absent or small-sized contralateral testis was first described by Laron and Zilka in 1969 [9]. Testicular volumes can be measured using different types of orchidometers or calipers. Prader’s orchidometer is the most widely used; nevertheless, US measurements of testicular volume are highly accurate, reproducible, and considered by many authors the best tool for measuring the testicular volume [10].

Seventy-six patients were included in our study in two consecutive years with an average age ranging between 6 months and 4 years in comparison to a study conducted by Shalaby et al. who included only 40 patients within 2 years with an age ranging between one and 6 years old [11]. The testicular volume in that study ranged from 0.94 to 6.33, with a mean of 3.12 ± 1.41 cm3. The difference compared to ours may be attributed to higher age groups being included in that study.

The result of laparoscopic exploration revealed 47% with absent testis and 53% with their testis present. This is approximately similar to the findings in other related studies as shown by AbdElsalam et al. who found the testis in about 57.5% of their studied patients and an absent testis in the remaining 42.5% [12].

The testicular volume as measured by US was significantly higher in those patients who had been found to have an absent testis (blind ending vas and vessels) or an excised atrophied canalicular remnant than in those who had a testis either intra-abdominal or passing into the inguinal canal. This confirms the concept of the importance of testicular hypertrophy in predicting the condition of its contralateral one as concluded also by Boehm et al. in their study [5].

The cut-off point of volume of normal testis in our study was ≤ 0.674 cm; this volume differs greatly from other studies as concluded by Hodhod et al. in their study in which the cut-off point was > 2 ml. However, in this study, the authors used Takihara orchidometer for measuring the testicular volume [13]. Although this orchidometer is useful in comparing different testicular sizes; nevertheless, the absolute values obtained are overestimated in many clinical conditions [14].

The estimated sonographic volume of the normal testis (cut-off point ≥ 0.674 cm) cm predicted significantly the condition of its contralateral impalpable one in our study. This is supported by the findings of Y. Wei et al. cut-off point > 0.65 cm) who concluded in their study that this estimate can predict significantly monorchism. Despite their findings, they emphasized the importance of laparoscopic exploration [15].

The laparoscopic exploration revealed closed DIR on the impalpable side in about 68% of our studied patients with significantly larger estimated testicular volume in those with closed ring 0.81 ± 0.22 than in patients with patent ring 0.54 ± 0.17. Ueda et al. concluded in their study evaluating the importance of the condition of DIR in case of unilateral impalpable testis that a closed DIR denotes the presence of an extra-abdominal nubbin or even absent findings and hence inguinal exploration in such cases could be avoided [16]. On the other hand, a survey involving more than 400 surgeons, around 92% and 75% of respondents preferred to explore the inguinal canal in case of open and closed DIR, respectively. This is because they believe that intracanalicular atrophic testis carry the risk of developing testicular cancer in the future [17].

The sensitivity of preoperative estimated testicular size at a cut-off point ≥ 0.674 cm in our study was 75% in the prediction of absent or atrophic contralateral impalpable one. This accuracy rate is considered intermediate among other studies as a higher accuracy (90%) was concluded by Hurwitz et al. in their study at a cut-off point of > 1.8 cm [8]. On the other hand, a study conducted by Hodhod et al. declared a sensitivity of 71.7% at a cut point-off > 2 ml [13]. In a more recent systematic review, it was concluded that defining a cut point for confirming contralateral testicular hypertrophy cannot demonstrate the condition of monorchism [18].

Hurwitz et al. concluded in their study that despite contralateral testicular hypertrophy can predict an absent contralateral one -in patients presented with unilateral impalpable undescended testis- with an accuracy of 90%, they recommended exploratory laparoscopy as it is the only diagnostic tool which could be done in such cases [8].