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Anatomy and function of scrotal ligament
ANATOMY AHMED From Cairo
AND FUNCTION
SHAFIK,
M.B.,
B.CH.,
D.S.,
OF SCROTAL LIGAMENT M.CH.
the Department of Surgery, University, Cairo, Egypt
ABSTRACT - The anatomy of the scrotal ligament has been studied in 22 cadavers by dissection and histologic examination. The ligament could be identijed in 20 cadavers. It binds the scrotal skin j%-mly to the tunica vaginalis at the lower testicular pole. The embryonic nature of the ligament is discussed. It synchronizes the cremasterico-dartos action under normal and varied temperatures. Absence of the ligament results in disordered testicular thermoregulation and may be a factor in the genesis of subfertility; the mechanisms involved are discussed. The difference between the aligamentous testicle and the high scrotal undescended testicle is discussed.
A previous study has demonstrated that a fibromuscular band, the “scrotal ligament,” connects the dartos closely with the tunica vaginalis at the lower testicular po1e.l A mention of such a ligament could not be traced in the medical literature, although it has been described in bovine animals.’ A study was made of the surgical anatomy of the scrotal ligament to elucidate its function in the light of its structure. Material
/ JUNE1977
Results A scrotal ligament was identified in 20 cadavers and was absent in two (Figs. 1 and 2). It was
and Methods
The material comprised 22 cadavers with normal scroti. Since each side was separately studied, this constituted 44 specimens. Ten cadavers were children with average age of five years, and twelve cadavers were adults with average age of forty-six years. The study consisted of direct dissection of specimens from one scrotal compartment and histologic examination of specimens from the opposite compartment. The dissected skin of the scrotal compartment was incised longitudinally on its anterolateral aspect from the superficial inguinal ring down to and a little above the scrotal bottom. The skin was reflected, and its relation to the underlying testicle and spermatic cord was studied especially the location, attachments, and morphology of the scrotal ligament. For the histologic study, the ligament was isolated with attached strips of the scrotal skin and tunica vaginalis at its ends. Serial lon-
UROLOGY
gitudinal and transverse cut sections were examined microscopically after they were stained with hematoxylin and eosin and Verhoeff-van Gieson for collagen and elastic and muscle fibers.
I VOLUMEIX,
NUMBER6
FIGURE 1. Diagram showing scrotal ligament that not only binds testicle to dartos but acts as connection along testicle between dartos and cremasteric muscles.
651
FIGURE 2. Longitudinal section of scrotal ligament of three-year-old: (a) scrotal skin and dartos, (b) scrotal ligament, and (c) tunica vaginalis and testicle (hematoxylin and eosin stain, x 2).
652
grayish white in adults and pinkish grey and relatively longer and more stretchable in children (Fig. 3). It varied in length from 0.5 to 1 cm. in children and from 1 to 2 cm. in adults. The ligament base was attached to the skin at the bottom of the scrotal compartment, along an area of from 2 to 5 mm. in children and from 0.5 to 1 cm. in adults. As the ligament left the scrotal skin, it penetrated the fasciomuscular tube and was attached to the parietal layer of the tunica vaginalis at its lower pole. It was surrounded by loose areolar tissue. When the testicle was drawn up, the scrotal skin dimpled at the ligament site; this was marked in adults. The long and stretchable ligament in children allowed the testicle to glide up for a considerable distance before the skin dimpled. Apart from the ligament site, the scrotal skin was loosely connected to the underlying fasciomuscular tube by areolar tissue and could be peeled off easily. The areolar tissue was more dense in adults than in children; this as well as the long and stretchable ligament explain that delivery of the testicle and cord outside the scrotum is easier in children than in adults.
UROLOGY
/ JUNE1977
! VOLUMEIX,
Nlk
FIGURE 4. Photomicrographs of scrotal ligaments: (A) child showing ligament of collagen impregnated with elastic and muscle fibers (X 220); (B) adult showing ligament of collagen and elastic fibers with Gieson no muscle fiber (X 175). (Verhoeff-van stains. )
Histologically, the ligament consisted of collagen impregnated with elastic and smooth muscle fibers; the latter was abundant in children (Fig. 4A). In adults, the muscle bundles diminished and were absent in some cadavers (Fig. 4B). The testicles were normally located in the scrotum in all the cadavers except the two aligamentous cases. However, they were slightly elevated in children because of the long and stretchable ligament. The two aligamentous cadavers were adults, thirty-six and forty-two years old. The testicles were high in the scrotum. The areolar tissue binding the scrotal skin to the fasciomuscular tube was minimal. The lower scrotal compartment was well developed but collapsed, and its skin was smooth and redundant. Biopsies from the dartos and cremasteric muscles of the two aligamentous cadavers were compared with those taken from 5 cadavers with scrotal ligaments. The two muscles from the aligamentous cadavers showed atrophy with fibrous tissue replacement. Comment The findings from this study suggest that the scrotal ligament is a remnant of the gubernaculum as evidenced from: (1) the ligament occurs at the anatomic site of the gubernaculum,
UROLOGY
/ JUNE 1977 / VOLUME
IX, NUMBER
6
(2) the histologic structure of both is the same, and (3) the ligament is more developed and muscular in children than adults. The precise function of the gubernaculum is still a controversy. Some investigators believe that it pulls the testicle down to the scrotum,3p4 others deny this.5,6 The present concept is that the function of the gubernaculum is to anchor the testicle to the scrotum through the scrotal ligament rather than to bring it down. Scrotal
Ligament in Testicular Thermoregulation
The ligament plays a significant role in the temperature-regulating mechanism of the testicle. Since it is attached to the testicle and dartos, it provides a mechanism which keeps the testicular movements in harmony with those of the dartos. In addition, it constitutes a “connection,” along the testicle between the dartos and cremasteric muscles (Fig. 1); such a connection synchronizes the action of the two muscles. The mechanism of ligament action requires special mention. The testicle is normally kept in the scrotum in a position which maintains a constant scrotal-rectal temperature difference under varied environmental temperature. This is brought about by the simultaneous cremasteric and dartos contraction or relaxation, the
653
FIGURE 5. Diagram of function of scrotal ligament as cremasterico-dartos synchronizer: (A) at rest, (B) under heat effect with synchronous cremastericodartos relaxation, and (C) under cold effect with synchronous cremastericodartos contraction.
FIGURE 6. Diagram of effect of absent scrotal ligament on testicular thermoregulation: (A) at rest, high testicle and redundant scrotal skin; (B) heat exposure, irrelevant cremasterice-dartos relaxation; and (C) cold exposure, cremasterico-dartos contraction .
c
A
synchronous action of the two muscles being mediated through the scrotal ligament (Fig. 5). Thus under normal temperature the scrotal ligament keeps the testicle in the scrotum in a position which results from the resting tone of both the cremasteric and dartos muscles. Under heat effect, dartos relaxation pulls down the ligament which not only pulls the testicle but potentiates cremasteric relaxation. Cremasteric contraction due to exposure to cold elevates the testicle which pulls up the ligament as well as the dartos, enhancing its contraction. Absent
Ligament
Absent ligament cent of the studied
654
in Subfertility
was encountered in 9 per series. This is probably due
to extension of the process of gubernacular degeneration to involve the ligament. The testicles were high in the scrotum and the lower scrotum hung curtain-like. Absent ligament may lead to disordered testicular thermoregulation and subfertility. The mechanism involved requires discussion. As a result of absent ligament, the cremastericodartos synchronous action is lost, and the two muscles do not function coordinately (Fig. 6). Thus, at rest the testicle tends to elevate toward the abdomen because the cremasteric tone is unopposed by the dartos, since the connection between the two muscles along the ligament is lost. In the meantime, the scrotal skin becomes redundant due to the unopposed dartos tone.
UROLOGY
/ JUNE1977
/ VOLUMEIX,
NUMBER6
FIGURE 7. Sterile patient with high testicle and curtain scrotum at normal environmental temperature: (A), and anteroposterior lateral (B) views. Exploration revealed absent scrotal ligament.
The picture at rest c a liigh testicle with .edundant, empty and ci t I,iiil-like lower scrots I comLosition disturbs sperpartment. ?‘his le testicle is kept c ose to matogenesis since the warm bocly sur*,we. On exposure t ) heat and cremaste -ice-dJntos relaxation, the scrotal skin elongate:, yet lie testicle does not follow since the ligament ::onnecting both is ; bsent. The testicle is lov+c red only to the ext :nt allowed by cremastt ric relaxation. This I 3sition would disturb heat radiation and testicuh r aeration. On exposure to cold and cremas:ericodartos contraction, Testicular elevation i exagacts on 1 free gerated as the ( remaster aligamentous testicle unconnected to the scrotal skin. The testicles :nay be elevated to lie at the external ring. Besides disturbiiis spermatogenesis, tl ie prolonged high testicular position at rest :reates organic changes in the spermatic cord and the scrotal wall. The fas;ciomuscular tube, es] lecially its cremasteric component, becomes con tracted and atrophies so th,It its reaction to temp :rature variations is deranged. Since the lower scrotal compartment is empty, its skin, includ ng the dartos, undergoes trophic changes from disuse, becomes smooth and redundant, and hangs curtain-like, a pictlire occasionally seen In subfertile patients (Fig. 7). Aligamentous
and Undescended
Test- cles
The aligamentous testicle has to be differentiated from the high scrotal undescende 1 testicle which is located at the external rir g. The etiology and clinical picture are different in both conditions. In the aligamentous testi’ :le the mechanism of testicular descent is norrr al, and the testicle descends to its normal scrot d position but is unfixed because of absent scrs Btal ligament. The condition is bilateral, a Id the scrotal compartments are well developc d. The
spcrma t ic cord has a normal length especially in early c ises, and the testicle can be easily persuaded clown into the scrotum. ‘The high scrotal undescended testicle fails front tl e start to descend to its normal position in the
AND FUNCTION
SHAFIK,
M.B.,
B.CH.,
D.S.,
OF SCROTAL LIGAMENT M.CH.
the Department of Surgery, University, Cairo, Egypt
ABSTRACT - The anatomy of the scrotal ligament has been studied in 22 cadavers by dissection and histologic examination. The ligament could be identijed in 20 cadavers. It binds the scrotal skin j%-mly to the tunica vaginalis at the lower testicular pole. The embryonic nature of the ligament is discussed. It synchronizes the cremasterico-dartos action under normal and varied temperatures. Absence of the ligament results in disordered testicular thermoregulation and may be a factor in the genesis of subfertility; the mechanisms involved are discussed. The difference between the aligamentous testicle and the high scrotal undescended testicle is discussed.
A previous study has demonstrated that a fibromuscular band, the “scrotal ligament,” connects the dartos closely with the tunica vaginalis at the lower testicular po1e.l A mention of such a ligament could not be traced in the medical literature, although it has been described in bovine animals.’ A study was made of the surgical anatomy of the scrotal ligament to elucidate its function in the light of its structure. Material
/ JUNE1977
Results A scrotal ligament was identified in 20 cadavers and was absent in two (Figs. 1 and 2). It was
and Methods
The material comprised 22 cadavers with normal scroti. Since each side was separately studied, this constituted 44 specimens. Ten cadavers were children with average age of five years, and twelve cadavers were adults with average age of forty-six years. The study consisted of direct dissection of specimens from one scrotal compartment and histologic examination of specimens from the opposite compartment. The dissected skin of the scrotal compartment was incised longitudinally on its anterolateral aspect from the superficial inguinal ring down to and a little above the scrotal bottom. The skin was reflected, and its relation to the underlying testicle and spermatic cord was studied especially the location, attachments, and morphology of the scrotal ligament. For the histologic study, the ligament was isolated with attached strips of the scrotal skin and tunica vaginalis at its ends. Serial lon-
UROLOGY
gitudinal and transverse cut sections were examined microscopically after they were stained with hematoxylin and eosin and Verhoeff-van Gieson for collagen and elastic and muscle fibers.
I VOLUMEIX,
NUMBER6
FIGURE 1. Diagram showing scrotal ligament that not only binds testicle to dartos but acts as connection along testicle between dartos and cremasteric muscles.
651
FIGURE 2. Longitudinal section of scrotal ligament of three-year-old: (a) scrotal skin and dartos, (b) scrotal ligament, and (c) tunica vaginalis and testicle (hematoxylin and eosin stain, x 2).
652
grayish white in adults and pinkish grey and relatively longer and more stretchable in children (Fig. 3). It varied in length from 0.5 to 1 cm. in children and from 1 to 2 cm. in adults. The ligament base was attached to the skin at the bottom of the scrotal compartment, along an area of from 2 to 5 mm. in children and from 0.5 to 1 cm. in adults. As the ligament left the scrotal skin, it penetrated the fasciomuscular tube and was attached to the parietal layer of the tunica vaginalis at its lower pole. It was surrounded by loose areolar tissue. When the testicle was drawn up, the scrotal skin dimpled at the ligament site; this was marked in adults. The long and stretchable ligament in children allowed the testicle to glide up for a considerable distance before the skin dimpled. Apart from the ligament site, the scrotal skin was loosely connected to the underlying fasciomuscular tube by areolar tissue and could be peeled off easily. The areolar tissue was more dense in adults than in children; this as well as the long and stretchable ligament explain that delivery of the testicle and cord outside the scrotum is easier in children than in adults.
UROLOGY
/ JUNE1977
! VOLUMEIX,
Nlk
FIGURE 4. Photomicrographs of scrotal ligaments: (A) child showing ligament of collagen impregnated with elastic and muscle fibers (X 220); (B) adult showing ligament of collagen and elastic fibers with Gieson no muscle fiber (X 175). (Verhoeff-van stains. )
Histologically, the ligament consisted of collagen impregnated with elastic and smooth muscle fibers; the latter was abundant in children (Fig. 4A). In adults, the muscle bundles diminished and were absent in some cadavers (Fig. 4B). The testicles were normally located in the scrotum in all the cadavers except the two aligamentous cases. However, they were slightly elevated in children because of the long and stretchable ligament. The two aligamentous cadavers were adults, thirty-six and forty-two years old. The testicles were high in the scrotum. The areolar tissue binding the scrotal skin to the fasciomuscular tube was minimal. The lower scrotal compartment was well developed but collapsed, and its skin was smooth and redundant. Biopsies from the dartos and cremasteric muscles of the two aligamentous cadavers were compared with those taken from 5 cadavers with scrotal ligaments. The two muscles from the aligamentous cadavers showed atrophy with fibrous tissue replacement. Comment The findings from this study suggest that the scrotal ligament is a remnant of the gubernaculum as evidenced from: (1) the ligament occurs at the anatomic site of the gubernaculum,
UROLOGY
/ JUNE 1977 / VOLUME
IX, NUMBER
6
(2) the histologic structure of both is the same, and (3) the ligament is more developed and muscular in children than adults. The precise function of the gubernaculum is still a controversy. Some investigators believe that it pulls the testicle down to the scrotum,3p4 others deny this.5,6 The present concept is that the function of the gubernaculum is to anchor the testicle to the scrotum through the scrotal ligament rather than to bring it down. Scrotal
Ligament in Testicular Thermoregulation
The ligament plays a significant role in the temperature-regulating mechanism of the testicle. Since it is attached to the testicle and dartos, it provides a mechanism which keeps the testicular movements in harmony with those of the dartos. In addition, it constitutes a “connection,” along the testicle between the dartos and cremasteric muscles (Fig. 1); such a connection synchronizes the action of the two muscles. The mechanism of ligament action requires special mention. The testicle is normally kept in the scrotum in a position which maintains a constant scrotal-rectal temperature difference under varied environmental temperature. This is brought about by the simultaneous cremasteric and dartos contraction or relaxation, the
653
FIGURE 5. Diagram of function of scrotal ligament as cremasterico-dartos synchronizer: (A) at rest, (B) under heat effect with synchronous cremastericodartos relaxation, and (C) under cold effect with synchronous cremastericodartos contraction.
FIGURE 6. Diagram of effect of absent scrotal ligament on testicular thermoregulation: (A) at rest, high testicle and redundant scrotal skin; (B) heat exposure, irrelevant cremasterice-dartos relaxation; and (C) cold exposure, cremasterico-dartos contraction .
c
A
synchronous action of the two muscles being mediated through the scrotal ligament (Fig. 5). Thus under normal temperature the scrotal ligament keeps the testicle in the scrotum in a position which results from the resting tone of both the cremasteric and dartos muscles. Under heat effect, dartos relaxation pulls down the ligament which not only pulls the testicle but potentiates cremasteric relaxation. Cremasteric contraction due to exposure to cold elevates the testicle which pulls up the ligament as well as the dartos, enhancing its contraction. Absent
Ligament
Absent ligament cent of the studied
654
in Subfertility
was encountered in 9 per series. This is probably due
to extension of the process of gubernacular degeneration to involve the ligament. The testicles were high in the scrotum and the lower scrotum hung curtain-like. Absent ligament may lead to disordered testicular thermoregulation and subfertility. The mechanism involved requires discussion. As a result of absent ligament, the cremastericodartos synchronous action is lost, and the two muscles do not function coordinately (Fig. 6). Thus, at rest the testicle tends to elevate toward the abdomen because the cremasteric tone is unopposed by the dartos, since the connection between the two muscles along the ligament is lost. In the meantime, the scrotal skin becomes redundant due to the unopposed dartos tone.
UROLOGY
/ JUNE1977
/ VOLUMEIX,
NUMBER6
FIGURE 7. Sterile patient with high testicle and curtain scrotum at normal environmental temperature: (A), and anteroposterior lateral (B) views. Exploration revealed absent scrotal ligament.
The picture at rest c a liigh testicle with .edundant, empty and ci t I,iiil-like lower scrots I comLosition disturbs sperpartment. ?‘his le testicle is kept c ose to matogenesis since the warm bocly sur*,we. On exposure t ) heat and cremaste -ice-dJntos relaxation, the scrotal skin elongate:, yet lie testicle does not follow since the ligament ::onnecting both is ; bsent. The testicle is lov+c red only to the ext :nt allowed by cremastt ric relaxation. This I 3sition would disturb heat radiation and testicuh r aeration. On exposure to cold and cremas:ericodartos contraction, Testicular elevation i exagacts on 1 free gerated as the ( remaster aligamentous testicle unconnected to the scrotal skin. The testicles :nay be elevated to lie at the external ring. Besides disturbiiis spermatogenesis, tl ie prolonged high testicular position at rest :reates organic changes in the spermatic cord and the scrotal wall. The fas;ciomuscular tube, es] lecially its cremasteric component, becomes con tracted and atrophies so th,It its reaction to temp :rature variations is deranged. Since the lower scrotal compartment is empty, its skin, includ ng the dartos, undergoes trophic changes from disuse, becomes smooth and redundant, and hangs curtain-like, a pictlire occasionally seen In subfertile patients (Fig. 7). Aligamentous
and Undescended
Test- cles
The aligamentous testicle has to be differentiated from the high scrotal undescende 1 testicle which is located at the external rir g. The etiology and clinical picture are different in both conditions. In the aligamentous testi’ :le the mechanism of testicular descent is norrr al, and the testicle descends to its normal scrot d position but is unfixed because of absent scrs Btal ligament. The condition is bilateral, a Id the scrotal compartments are well developc d. The
spcrma t ic cord has a normal length especially in early c ises, and the testicle can be easily persuaded clown into the scrotum. ‘The high scrotal undescended testicle fails front tl e start to descend to its normal position in the