Persistence of the processus vaginalis and its related disorders

Abstract

The processus vaginalis is a blind‐ended evagination of the abdominal wall that develops during fetal life and typically undergoes obliteration in early life. Persistence of the processus vaginalis is associated with a number of pathologies including congenital indirect inguinal hernias, communicating hydroceles, funicular and encysted hydroceles, canal of Nuck cysts, and acquired undescended testis. Whilst all are detectable sonographically, there is little educational material relevant to the field of ultrasound with much of the literature directed at surgical and primary care physicians. Furthermore, within the literature there is a lack of consensus on several areas including the anatomy and embryology of the processus vaginalis and the mechanisms behind its obliteration. As such the objective of this paper is to distil the information regarding the persistent processus vaginalis as it is relevant to ultrasound and in doing so address the literature gap for sonographers and sonologists. The anatomy and embryology of the persistent processus vaginalis will be discussed including causative mechanisms for anomalies with their sonographic appearance highlighted.

Introduction

In normal development, the processus vaginalis, with the exception of the tunica vaginalis in males, is obliterated in early life.1, 2, 3 When obliteration fails, a spectrum of conditions associated with its persistence may occur.4, 5 These include indirect inguinal hernias, hydroceles, cysts, and acquired undescended testes.4 Non‐obliteration is also at least partially implicated in cryptorchidism, retractile testis, and a range of epididymal anomalies detectable sonographically.4, 6, 7, 8, 9

The processus vaginalis and its role

The processus vaginalis forms in both males and females; however, it is believed to be closely linked to testicular descent as it is found in all species where the male gonad descends through an inguinal canal.8 Whilst consensus has not been reached on its role, it appears to act, with the gubernaculum, in dilating a pathway for testicular descent through the inguinal canal and into the scrotum.10 In females, the processus vaginalis, known as the canal of Nuck, is smaller and more rudimentary than in males.11, 12 The canal of Nuck accompanies the gubernaculum which differentiates to become the round ligament of the uterus.5, 11, 12 It has been proposed that it assists the gubernaculum in the normal anteverted, anteflexed positioning of the uterus and in preventing ovary descent into the inguinal canal.7, 13

Embryology of the processus vaginalis

The majority of anomalies related to the processus vaginalis are associated with its persistence.4, 5 An understanding of the embryological development of the processus vaginalis is, therefore, key to understanding the anomalies that occur when obliteration fails.

The processus vaginalis begins forming in the 8^th week after conception.8 It begins as a caudally directed outpouching of the peritoneum that attaches to the ventral surface of the developing gubernaculum.8 Following the gubernaculum, the processus vaginalis herniates through the abdominal wall carrying with it layers of muscle that include the transversalis fascia, the internal, and external oblique muscles.14 The entry point of herniation through the abdominal wall created by the processus vaginalis becomes the deep inguinal ring whilst the muscle layers carried with it form the inguinal canal.3 The processus vaginalis exits the abdominal wall through the aponeurosis of the external oblique muscle at the superficial inguinal ring.3

In the third trimester, the processus vaginalis and gubernaculum extend further down into the scrotum with the processus vaginalis acting as a conduit to transmit intra‐abdominal pressure to the testes.8, 15 This pressure provides a hydraulic force assisting their descent within or posterior to the processus vaginalis as seen in Figures 1 and 2.8, 15

Figure 1.

Development of processus vaginalis.

Figure 2.

Processus vaginalis prior to obliteration.

Obliteration of the processus vaginalis

Although obliteration may occur prenatally, in up to 80% of males and 60% of females, the process vaginalis is still present at birth.5, 16, 17. By 8 weeks of age, 63% of males will have a persistent processus vaginalis with obliteration occurring any time up until the age of two years.2 After this age, up to 40% of males continue to have a persistent process vaginalis with around half remaining asymptomatic throughout life.2, 16, 17, 18

Stages of obliteration

Obliteration occurs in three stages in males and two stages in females4, 7. The first step, common to both males and females, involves closure of the deep inguinal ring proximally, sealing off the processus vaginalis from the peritoneum.4 In males, this is followed by distal closure of the processus vaginalis, just superior to the testis. The remaining tubular structure between these two closures, the funicular process, undergoes atresia in the final stage of obliteration.19 The most distal portion of the processus vaginalis remains in place forming the tunica vaginalis as seen in Figure 3.20 In females, the second and final stage of obliteration is atresia of the canal of Nuck.7

Figure 3.

Completed obliteration of processus vaginalis.

Whilst the mechanisms are not yet fully elucidated, the process of obliteration involves programmed cell death of the smooth muscle cells of the processus vaginalis.21, 22 This apoptosis may occur due to a decrease in sympathetic and increase in parasympathetic innervation which in turn is stimulated by a cascade of hormones.20, 21, 23 The neurotransmitter, calcitonin gene‐related peptide, released by the genitofemoral nerve in the inguinal canal, appears to be the predominant hormone in stimulating closure and obliteration of the processus vaginalis.24, 25

Failed obliteration – what can go wrong?

Non‐obliteration may occur during any stage with the pathology that results dependant on the stage of failure. Obliteration failures can occur in both left and right groins; however, a right‐sided patent processus vaginalis is 50% more common.26 The causes of non‐obliteration are not fully understood, however, failure of apoptosis (due to smooth muscle de‐differentiation), inadequate parasympathetic innervation, and lack of appropriate hormone signalling have each been implicated.8, 22, 23, 27 Although frequently idiopathic, premature birth, hip dysplasia, Ehlers‐Danlos syndrome, and Cystic Fibrosis are known to be associated with failed obliteration.20

When obliteration fails across all stages, the processus vaginalis remains patent from the deep inguinal ring to the scrotum or labia majora. This creates a potential space that communicates with the peritoneum and commonly results in indirect inguinal hernia and communicating hydroceles.4 Although rare, this communication can also allow the transport of infective processes into the scrotum or labia and implantation of endometriosis or ectopic pregnancies within the canal of Nuck.17, 28, 29, 30, 31, 32

When partial obliteration occurs, the result is a spectrum of anomalies reflective of the stage at which obliteration failed and includes hydroceles, cysts, and acquired undescended testis.4

Anomalies directly related to persistence of the processus vaginalis

Congenital inguinal hernia

Congenital inguinal hernias occur in up to 5% of children under 15 years of age.11 Boys are more susceptible with a 6:1 male to female ratio reported.33 In both sexes, right‐sided hernia are more common, possibly due to the typically later closure of the right processus vaginalis.4, 5 Premature infants have an increased risk with up to 30% born with an inguinal hernia.34 Whilst 90% of indirect inguinal hernias in adults are due to a persistent processus vaginalis, in the paediatric population this is almost always the cause.2, 5, 35, 36

Failure of closure of the processus vaginalis at the deep inguinal ring leaves an opening between the peritoneum and the inguinal canal, greatly increasing the likelihood of an indirect inguinal hernia in both paediatric and adult populations.2 Intra‐abdominal contents can enter this opening and, in a completely patent processus vaginalis, may extend to the scrotum or labia majus.37, 38 Intra‐abdominal contents may include omentum, intestinal loops, ovaries, uterus, uterine tubes, and the urinary bladder.37 This carries the risk of incarceration and strangulation.4, 38 As peritoneal fluid may also enter the patent processus vaginalis, communicating hydroceles frequently co‐exist with congenital inguinal hernias.36

The role of ultrasound in diagnosis of congenital indirect inguinal hernia

Although many inguinal hernias are clinically diagnosed, ultrasound can be used to confirm the diagnosis and to assess clinically equivocal cases.35 Ultrasound is also used in hernia patients to assess the contralateral inguinal canal for a contralateral patent processus vaginalis. As the incidence of a contralateral patent processus vaginalis is up to 50% in males and 90% in females, exploratory surgery to identify this is frequently performed at the time of hernia repair.33, 39 This allows for immediate surgical repair to prevent the development of a contralateral inguinal hernia which has an incidence of up to 31%.39 However, this exploration extends the surgery duration and introduces risk of surgical damage to neighbouring structures such the vas deferens and spermatic cord.1, 39, 40 Furthermore, false‐negative results can occur due to covering of the deep internal ring by a peritoneal veil (formed by the peritoneal fold in patients with a lateral umbilical ligament).39, 41

Ultrasound has been shown to be a promising tool in pre‐operative assessment for a contralateral patent processus vaginalis with a sensitivity of 93% and specificity of 88%.1, 11, 40 In studies where ultrasound demonstrated higher rates of false‐negatives, it remained able to accurately diagnose those contralateral patencies at higher risk of developing into hernias.1

Ultrasound appearance of congenital indirect inguinal hernias

The key sonographic features of an indirect inguinal hernia include visualisation of omentum and intestinal loops within the inguinal canal, possibly extending to the scrotum or labia.4 Omentum will be seen as echogenic tissue whilst intestinal loops appear as tubular or rounded structures with possible peristalsis or air bubbles.4, 35 Intra‐abdominal organs such as ovaries, uterus, or bladder may also enter the inguinal canal.35 If a hernia is reducible, contents may be visible only on Valsalva or in erect position.

Ultrasound criteria for diagnosing a contralateral patent processus vaginalis

Although the sonographic criteria for diagnosing a contralateral patent processus vaginalis varied among the studies reviewed, the visualisation of a hydrocele within the inguinal canal has been described as a definitive finding.11, 39, 42 If the diameter of the hydrocele, measured sonographically at the deep inguinal ring, is above 2 mm, it is considered at high risk of developing into a hernia.

In the absence of a hydrocele, any opening of the process vaginalis into the peritoneum measuring 4mm or greater is considered positive for a contralateral patent processus vaginalis.4, 11, 42

Acquired undescended testes

Acquired undescended testes describes the condition where testicles previously located in a normal scrotal position have since ascended.43 This occurs in up to 3% of males and may be associated with reduced fertility and increased risk of testicular malignancies.44

Acquired undescended testes occur due to an incomplete obliteration of the processus vaginalis that leaves a fibrous remnant of the funicular process along the spermatic cord.5 This fibrous tissue tethers the testis to the inguinal canal.43, 44 As the child grows, the tethered testis is effectively pulled out of the lower scrotum.43 Initially, the testis may be found in a high scrotal position but as continued somatic growth occurs it is pulled into an inguinal position.43

Ultrasound features of acquired undescended testes

Acquired undescended testes may be located in a high scrotal or inguinal position.43 A heterogeneous testis may be seen with a reduced volume in comparison to a contralateral normally descended testis.44 Reduced epididymal diameter in comparison to a contralateral epididymis may also be found.44

It may be possible to manipulate an acquired undescended testis into the normal, mid‐to‐low scrotal position. This can result in its misdiagnosis as a retractile testis so caution when scanning, particularly with transducer pressure, is required. Unlike a retractile testis, an acquired undescended testis will never be found at rest in the normal scrotal position. Furthermore, resistance or tightness of the spermatic cord may be felt when manipulating the testis into the scrotum and when released it will spring back to a suprascrotal location.45

Communicating hydrocele

When obliteration fails across all stages, peritoneal fluid can enter the deep inguinal ring and flow into the scrotum via the patent processus vaginalis. When this occurs without intra‐abdominal contents, it is known as a communicating hydrocele as seen in Figure 4a–c. This may present as a painless and intermittent bulge in the inguinal region or scrotum.18

Figure 4.

(a) A communicating hydrocele in an adult male with history of a painless, fluctuating right scrotal swelling. Fluid is seen within the patent processus vaginalis (star) entering at the deep inguinal ring (arrow) and extending distally. (b) Fluid shown extending through the superficial inguinal ring (arrow). (c) Fluid (asterisk) extends into the right hemi‐scrotum surrounding the right testis (RT). Fluid was seen to increase in volume on Valsalva.

A noteworthy complication of a communicating hydrocele is that in providing a channel between peritoneum and scrotum, it allows infection, blood, peritoneal dialysis fluid, and even ventricoperitoneal shunts to track down to the scrotum.17, 29 Although uncommon, a number of cases are reported of acute scrotum presentations with an intra‐abdominal cause.17, 26, 29 In particular, appendiceal perforation may present as an acute scrotum due to the transport of the infective process via a patent processus vaginalis.17, 29

Ultrasound features of a communicating hydrocele are listed in Table 1 below.

Table 1.

Ultrasound appearance of hydroceles caused by a persistent processus vaginalis.

Type	Location	Appearance	Reducible?
Communicating hydrocele	Extends from peritoneal opening at deep inguinal ring into scrotum.	Well defined, anechoic fluid with low‐level echoes possible due to protein content. May contain haemorrhage or pus from peritoneum in acute conditions.17	Yes. Fluid may only be visible on Valsalva, in erect position and/or with minimal probe pressure.
Funicular hydrocele	Extends from peritoneal opening at deep inguinal ring to just superior to scrotum	Anechoic fluid as above. Ovoid or tubular, may resemble peritoneal diverticulum.4, 20, 46 May have beaded appearance at proximal end due to fibrous adhesions.4, 46	Yes. As above
Encysted hydrocele	Between deep inguinal ring to just superior to scrotum	Round or ovoid anechoic fluid filled mass.18, 20	No. Volume will not change on Valsalva but may be slightly mobile.
Canal of Nuck hydrocele	Extends from peritoneal opening at deep inguinal ring to labia majora	Tubular, ovoid, mushroom, or comma/speech bubble shape. Thin walled with possible internal septa.4, 13, 47, 51 Anechoic fluid, possible low‐level echoes due to protein content.	Yes. Fluid may only be visible on Valsalva, in erect position and/or with minimal probe pressure.
Canal of Nuck cyst	Inguinolabial region	Round, ovoid, mushroom, or comma/speech bubble shape. Thin walled with anechoic fluid.4, 13, 47	No. Volume will not change on Valsalva but may be slightly mobile.

Funicular hydrocele

When obliteration occurs above the testis but fails at the deep inguinal ring and funicular process, peritoneal fluid may flow through the patent processus vaginalis without entering the scrotum.46 This is known as a funicular hydrocele as seen in Figures 5a‐6c. It may present as a painless and fluctuating bulge in the inguinal region that does not extend into the scrotum. Ultrasound features of a funicular hydrocele are listed in Table 1 below.

Figure 5.

(a) A funicular hydrocele in a 2‐year‐old boy with a history of a fluctuating right inguinal swelling. At rest, fluid is visible within a patent processus vaginalis (star) at the deep inguinal ring and proximal portion of the right inguinal canal. Fluid does not extend to the right testis (RT). (b) Fluid now visualised extending from the peritoneum (asterisk) distally within the patent processus vaginalis (star). (c) With abdominal pressure, fluid volume increases extending distally within the patent processus vaginalis (star) without entering the scrotum. This indicates that obliteration failed both in closure of the deep inguinal ring and atresia of the funicular process but completed just superior to the testis (RT) as shown by the arrow.

Figure 6.

(a) A funicular hydrocele in an 8‐year‐old boy presenting with intermittent right‐sided inguinal mass. Distally a remnant of partial obliteration can be seen as a septation or fibrous adhesion (arrow). (b) Although fluid can be seen superior to the right testis (RT), it did not surround the testis. This indicates that closure of the processus vaginalis was completed superior to the testis as indicated by the arrow. (c) Proximally the processus vaginalis appears collapsed (asterisk) however on Valsalva the volume of fluid increased indicating patency of the funicular process at the deep inguinal ring.

Encysted hydrocele

When closure occurs both at the deep inguinal ring and directly above the testis, an encysted hydrocele may result.20 This represents a fluid collection within the remaining patent processus vaginalis and may present as a painless, mobile, and cystic swelling.8 Ultrasound features of an encysted hydrocele are listed in Table 1 below.

Canal of Nuck hydroceles and cysts

When complete failure of obliteration occurs in females, the deep inguinal ring remains patent allowing the flow of intraperitoneal fluid into the canal of Nuck. The resulting hydrocele is the homologue to communicating hydroceles in males and typically presents as a non‐tender, reducible mass in the inguinolabial region.47 As with males, this communication with the abdomen also enables the transport of other substances into the region. This can include haemorrhage or purulent fluids resulting in acute presentations such as a labial abscess.48 Although rare, it may also allow for implantation of endometriosis or ectopic pregnancy within the canal of Nuck.28, 32

With partial failure of obliteration, closure occurs only at the deep inguinal ring leaving the canal of Nuck patent. Fluid may become trapped or accumulate resulting in a canal of Nuck cyst.49, 50 This may present as a tense, irreducible mass within the inguinolabial region. Ultrasound features of a canal of Nuck hydroceles and cysts are listed in Table 1 below.

Conclusion

Persistence of the processus vaginalis beyond fetal life is common and can result in a spectrum of pathologies that are sonographically detectable. The most prevalent of these is the indirect inguinal hernia commonly encountered in both the paediatric and adult population. Additionally, a range of hydroceles and cysts may also occur together with acquired undescended testes. An adequate knowledge of the anatomy and embryology of the processus vaginalis and the causative mechanisms of obliteration and non‐obliteration can assist ultrasound practitioners in understanding and assessing these pathologies.

Authorship declaration

Ms Brainwood, Ms Beirne and Ms Fenech are in agreement both that the authorship conforms with AJUMs authorship policy and with the content of the submitted manuscript.

Funding

No funding information is provided.

Conflict of interest

No conflicts of interest to disclose.