Keywords
round ligament - processus vaginalis - ultrasonography - magnetic resonance imaging
- laparoscopy - canal of Nuck - leiomyoma - gubernaculum
Introduction
The round ligament forms the superior margin of the broad ligament and connects the
uterine cornu to the mons pubis. They are a pair of fibromuscular cord-like structures
derived from the gubernaculum and serve as a secondary support system for the uterus.
The round ligaments have varied clinical and surgical implications. The involvement
of round ligaments by pathological processes is underestimated. They are involved
in spreading diseases, as sites for primary neoplasms, and serve as landmarks in differentiating
lesions. Imaging modalities, especially magnetic resonance (MR) aid in visualization
and evaluation of normal and abnormal round ligament, resulting in better prognostication
and management of disease conditions. This article aims to provide a comprehensive
review of anatomy, embryology of the round ligaments, its implications, and the role
of imaging in related disorders.
Embryology and Anatomy of Round Ligaments and Related Structures
Embryology and Anatomy of Round Ligaments and Related Structures
Round ligaments are a pair of 10- to 12-cm-long cord-like fibromuscular structures
that connect the uterine cornu to the labia majora.[1] They are derived from the gubernaculum and represent the remnant of the same. The
gubernaculum and processus vaginalis develop during the eighth week of fetus development
([Fig. 1]). The gubernaculum is attached to the inferior pole of the gonads. In males, it
directs and creates a passage for the descent of the testis into the scrotum coursing
through the inguinal canal. In females, mullerian development interferes with descent
and the ovaries are fixed higher up by the ovarian ligament, a proximal gubernaculum
derivative, while the distal portion remains as the round ligament merging with the
labial soft tissue. This entire process is facilitated by the processus vaginalis,
which is a ventral peritoneal outpouching that is attached to the gubernaculum. The
processus vaginalis carries the parietal wall layers, forming the inguinal canal.
It eventually gets obliterated in females ranging between the eighth month of gestation
to the first year of life, the persistence of which manifests as patent canal of Nuck.[2]
[3]
Fig. 1 The ovarian and round ligament are the gubernaculum derivatives. The round ligament
connects the uterine cornu, enters the inguinal canal, and merges with the labia majora
fat. On the right is the obliterated canal of Nuck, an ideal occurrence. On the left
is the patent canal, which can predispose to hernias and hydrocele. F, fallopian tube;
O, ovary.
The round ligament is covered by a fold of peritoneum forming the broad ligament ([Fig. 2]). The round ligament forms the superior margin of the broad ligament, which also
contains the fallopian tubes, vessels, nerves, and loose connective tissue.[1] Two-thirds of the round ligament is intraperitoneal, and one-third is extraperitoneal
in location. The portion distal to the deep inguinal ring, within the inguinal canal
and beyond, is extraperitoneal. This division is important as diseases that spread
via the round ligament once involve the extraperitoneal portion can require a change
in the management or more extensive treatment strategies.[4] The blood supply is by the Sampsons artery, a branch of the inferior epigastric
artery that runs along the round ligament and constitutes an anastomosis between the
uterine and the ovarian artery. The venous drainage is by the uterine vein or the
ovarian vein. The lymphatics drain through superficial inguinal nodes (extraperitoneal
portion) and internal iliac lymph nodes (intraperitoneal portion)[1]
Fig. 2 Laparoscopic image of the pelvic cavity: *, uterus; F, fallopian tubes; O, ovaries,
B, broad ligament; white arrows: round ligaments.
Imaging Appearances: Normal
Imaging Appearances: Normal
The imaging appearance of the normal round ligament reflects the histology. The ligament
is comprised of muscle fibers, fibrotic tissue, a few vessels, and nerves, and hence
appears as a smooth, hypointense band on both T1 and T2, which is made prominent by
the surrounding fat ([Fig. 3D–F]). From the uterine cornu on either side, they run anterior to the external iliac
vessels, within the inguinal canal, and ramify with the subcutaneous fat in the mons
pubis.[5] On computed tomography (CT), it appears isodense to the muscle surrounded by the
fat. The presence of ascites identifies the ligament easily ([Fig. 3A–C]). Ultrasound appearances are variable from iso- to hyperechoic and difficult to
delineate from adjacent fat unless accompanied by a patent canal that appears anechoic/hypoechoic.
Fig. 3 (A) Axial and (B, C) coronal computed tomography sections of the pelvis show round ligaments (white arrows) surrounded by fat, along the inguinal canal to merge with labial fat. Round white circles are inferior epigastric vessels. (D) Axial and (E) coronal T2 magnetic resonance imaging show hypointense smooth round ligaments (white arrows). (F) Coronal oblique postcontrast T1 with fat saturation shows homogenous and smooth
enhancement of the round ligaments (white arrow).
The thickness is variable with age and since the development parallels the mullerian
duct embryologically, the thickness probably corresponds to the size of the uterus.
The postmenopausal atrophic uterus has thin sometimes nontraceable round ligaments.
Any deviation from the normal hypointensity on MR should alert underlying pathology.
Clinical Implications of Round Ligament
Clinical Implications of Round Ligament
The round ligament along with the broad ligament offers secondary support system for
the uterus. The round ligament is implicated in maintaining the anteversion and anteflexion
of the uterus.[6] In a pregnant uterus, there is undue stretching and hypertrophy of the round ligament,
which can be symptomatic in some individuals, causing round ligament pain.
Plication of round ligaments or uterine ventrosuspension is indicated in retroverted
retroflexed uteri to manage dysmenorrhea and deep dyspareunia[7] ([Fig. 4A]). It is routinely done in cases of isthmocele with a retroverted uterus as ventrofixation
reduces the strain at the suture line and promotes better wound healing at the defected
uterine scar site.
Fig. 4 (A) Intraoperative image depicting oophoropexy (O) to round ligament (RL) done in cases
of recurrent ovarian torsion. (B) Combined ovarian ligament (OL) plication and round ligament oophoropexy. (C) Kakinuma method of vaginal vault fixation to the round ligament.
Combined utero-ovarian and round ligament oophoropexy is a novel oophoropexy procedure
that may reduce the risk of recurrent torsion[8] ([Fig. 4B]).
The Kakinuma method involves suturing and fixation of round ligaments on both sides,
effectively lifting the vaginal stump after laparoscopic hysterectomy[9] ([Fig. 4C]).
The round ligament can act as a route for the spread of diseases. Since it bridges
the intraperitoneal space to the extraperitoneal space, pathologies such as endometriosis,
infection, and malignant neoplasms can spread along the ligament and present as extraperitoneal
lesions or masses. Spread along the round ligaments is more favored on the right side
probably due to the direction of peritoneal fluid circulation and relative protection
on the left by the sigmoid colon[4]
[10]
Primary tumors of the round ligament are rare with leiomyoma and mesothelial cysts
among the common lesions reported in the literature.[11]
[12]
Persistence of the processus vaginalis beyond 1 year of life can result in congenital
hernias where the herniation is almost always through the canal of Nuck into the inguinal
canal lateral to the inferior epigastric vessels. Contents can be the intestine, genitalia,
or both. The latter if it contains ovaries carries the risk of torsion or ischemia.[2]
Round Ligament as a Landmark
Round Ligament as a Landmark
The round ligament serves as a surgical landmark to differentiate interstitial pregnancy
from angular pregnancy. It is essential to understand the differences since the management
and outcomes are different for each type of ectopic pregnancy.
Interstitial pregnancy is an ectopic pregnancy implanted in the interstitial part
of the fallopian tube and close to the uterine musculature and implant lateral to
the round ligament, whereas angular pregnancy (pregnancy in the normal cornual region
of the uterus) implants medial to the round ligament, at the lateral angle of the
endometrial/uterine cavity, and just medial to the uterotubal junction[13] ([Fig. 5]).
Fig. 5 (A) Laparoscopic image of interstitial pregnancy (*). (B) The relation of the gestational sac (*) to the round ligament (arrows) whose attachment is noted medial to the pregnancy differentiating from angular pregnancy.
True broad ligament fibroids arise from the intraperitoneal portion of the round ligament
or utero-ovarian ligament that contains smooth muscle cells. Distinction from false
broad ligament fibroids, which arise from the lateral wall of the uterus corpus or
cervix and bulge outward between the layers of broad ligament, is made by demonstrating
a groove between the uterus and the fibroid on laparoscopy, with the round ligament
inseparable from the mass[14] ([Fig. 6]). Additional demarcation is by demonstrating the relation of mass with the ureter,
which is medially displaced in a true broad ligament fibroid.
Fig. 6 (A) Intraoperative images of the pseudo-broad ligament fibroid arising from the right
lateral wall of the uterus. (B) True broad ligament fibroid arising in between the leaves of the broad ligament
and lateral to the ureter.
Since round ligaments can be easily identified on imaging modalities such as CT and
MR imaging (MRI), they can be used as landmarks to diagnose certain pathologies with
confidence.
Accessory and cavitated uterine mass (ACUM) is a rare mullerian anomaly where there
is a separate noncommunicating endometrium-lined cavity surrounded by myometrium-like
smooth cells, separate from the normal endometrial cavity. Patients present with dysmenorrhea
or postmenstrual pain.[15] This entity can be confused with cystic adenomyosis or red degeneration of the fibroid.
Confident diagnosis can be made on MR as ACUM typically presents as a lateral myometrial
mass below the round ligament attachment to the uterus[16]
[17] ([Fig. 7]).
Fig. 7 (A) Coronal and (B) axial T2-weighted image shows a well-defined cavitary mass containing hemorrhage
(*) indenting the normal endometrium (E) consistent with ACUM. White arrows point to the round ligament related superiorly to the mass. (C) Intraoperative image shows the relation of the cavity (*) to the round ligament
(white arrow).
Mayer–Rokitansky–Kuster–Hauser (MRKH) syndrome is one of the causes of primary amenorrhea
in adolescent girls who otherwise have normal secondary sexual characteristics. A
variable spectrum of imaging findings are seen including absent or hypoplastic uterus
with or without rudimentary horns. Rudimentary horns are common in MRKH in up to 92%
of cases.[18] They are seen as nodular masses isointense to myometrium with or without an endometrium
lining on either side consistently caudal to the corresponding ovary. The rudimentary
horns are in line/attached to the round ligaments explaining its location caudal to
the ovary. Interference in the nonunion of mullerian ducts probably leads to distal
migration of the rudimentary horns along the round ligament ([Fig. 8]). In suspected cases of MRKH, a careful review of MR images focusing along the round
ligaments is warranted to pick the rudimentary horns. [Table 1] summarizes the round ligament as a landmark and localizing tool.
Fig. 8 (A) Axial and (B) coronal T2-weighted magnetic resonance shows nodular isointense structures in the
lateral pelvic wall bilaterally (dashed arrows) located caudal to the ovaries (circle) and seen attached to the round ligament (solid arrow). (C) Inset shows the laparoscopic image of rudimentary horns (dotted arrow) attached to the round ligament (solid arrow).
Table 1
Round ligament as a landmark and localizing tool
|
Sl. no.
|
Condition
|
Clue
|
|
1
|
Interstitial and angular pregnancy
|
Implantation in interstitial pregnancy is lateral to the round ligament
|
|
2
|
True and false broad ligament fibroid
|
Presence of a groove between the uterus and the broad ligament in true fibroid and
may be inseparable from the round ligament if arising from the same
|
|
3
|
Accessory and cavitated uterine mass (ACUM)
|
Typically in the lateral myometrial wall below the curve of the round ligament separate
from the normal endometrial cavity
|
|
4
|
Rudimentary horns in MRKH (Mayer–Rokitansky–Kuster–Hauser) syndrome
|
Horns are seen along and attached to the round ligament
|
|
5
|
Right iliac fossa abscess
|
Differentiate between an abscess of appendicular or tubo-ovarian origin based on whether
the abscess is lateral or medial to the round ligament
|
Pathologies of Round Ligament: Role of Imaging
Pathologies of Round Ligament: Role of Imaging
Ultrasonography (USG) is the preferred initial imaging modality for female pelvic
pathologies. Although direct visualization of the intraperitoneal portion of the round
ligament is not possible on USG, the inguinal component is easily accessed due to
its superficial location. USG is especially reliable for the diagnosis of inguinal
masses related to round ligament including canal of Nuck cyst/hydrocele, congenital
hernias, lymphadenopathy, and tumors ([Fig. 9]).
Fig. 9 Ultrasonography of the left inguinal region in a female shows an elongated cystic
lesion (*) with thin septations, suggestive of canal of Nuck hydrocele.
CT poses radiation risk and offers relatively poor contrast for pelvic organ assessment.
Gross pathologies like mass, cyst, varices, or lymphadenopathy can be picked up ([Fig. 10]) and whenever feasible should be evaluated by MRI for better lesion characterization.
Fig. 10 (A) Axial, (B) sagittal, and (C) coronal contrast-enhanced computed tomography sections of the pelvis in a female
with inguinal swelling shows an elongated cystic lesion in the right inguinal region
with a “cyst in cyst” appearance (solid arrow) consistent with type 1 canal of Nuck hydrocele.
MRI is the preferred modality for the evaluation of round ligament–related pathologies
as it offers the best contrast resolution and lesion characterization. Basic sequences
along with susceptibility-weighted imaging (SWI), diffusion-weighted imaging, and
post-contrast-enhanced sequences with subtraction should be done ideally or tailored
according to the clinical suspicion ([Fig. 11]).
Fig. 11 (A) T2 axial section of the pelvis in a known case of endometriosis shows thickening
of the left round ligament (white arrows) suggesting possible involvement. (B) Susceptibility-weighted imaging confirms the presence of hemorrhagic foci (endometriotic
deposits) along the left round ligament (black arrow).
[Table 2] summarizes various round ligament–related pathologies.
Table 2
Various round ligament related pathologies
|
Infection
|
|
Endometriosis
|
|
Varices
|
|
Benign tumors: leiomyoma, mesothelial cyst, lipoma, dermoid, serous cystadenoma
|
|
Malignant
Primary: leiomyosarcoma, PEComa (perivascular epithelioid cell tumor)
Secondary: endometrial carcinoma, cervical carcinoma, ovarian epithelial carcinoma,
gastric adenocarcinoma, and gallbladder carcinoma
|
|
Canal of Nuck related: hernia, cyst/hydrocele
|
Infection
Uterine and adnexal infection (pelvic inflammatory disease) can spread along the round
ligament in similar means to tumor spread and can cause inguinal lymphadenopathy.[19] Involvement of the round ligament by the infectious process manifests as thickening
and enhancement of the ligament in contiguity with the primary disease process ([Fig. 12]). In the case of a right iliac fossa abscess of uncertain origin, displacement of
the round ligament can aid in differentiating a tubo-ovarian abscess from an appendicular
abscess in addition to other imaging features.[19] Knowledge about the extent of infection can help in management decisions and better
outcomes.
Fig. 12 (A, B) Axial and (C) coronal postcontrast T1 images show an infective collection in the right adnexa
(circle) with contiguous extension along the right round ligament that appears thickened
with enhancement (solid arrows) till its insertion to the mons. Dashed arrows indicate normal round ligaments on the left side.
Endometriosis
Deep infiltrating endometriosis predominantly affects the posterior structures such
as the torus uteri and uterosacral ligaments. Involvement of round ligaments has a
variable prevalence of 0.3 to 14%.[4] Since it is an atypical site of involvement with no specific clinical symptoms or
signs, round ligament involvement is often overlooked, resulting in incomplete surgical
clearance of the disease. In patients with coexisting endometriosis, dissemination
of endometrial cells along the round ligament from the abdominal cavity is the more
acceptable theory, and deposits are usually seen in the proximal part of the round
ligament and the inguinal canal.[20] Isolated involvement of the inguinal portion by endometriosis advocates for the
mullerianosis theory in patients without coexisting pelvic endometriosis.[21]
MR is the best modality for detecting round ligament involvement by endometriosis ([Fig. 13]). Common imaging findings are thickening, irregularity, and shortening of the ligament. T1 hyperintense foci, blooming of SWI, or just hypointense thickening
can be seen.[22]
[23] Surgical findings such as shortening, deviation, or thickening of the round ligaments
have high positive predictive values for the diagnosis of endometriosis.[24] It is important to describe the endometriotic involvement of round ligaments in
radiology reports to facilitate better surgical outcomes.[25]
Fig. 13 (A) Axial T1, (B) axial T2, and (C) coronal T2 images show significant thickening, irregularity, and tethering of the
left round ligament (solid arrow) in a case of deep endometriosis. “*” refers to left ovarian endometrioma. (D) Axial T1 with fat saturation shows the presence of T1 hyperintense foci along the
round ligament (dashed arrow) consistent with endometriotic deposits. (E) Intraoperative image showing endometriotic deposits involving the round ligament
(solid arrows).
Round Ligament Varices
Round ligament varices are exclusively seen in pregnancy, especially beyond the second
trimester due to hormonal influence and pressure on the pelvic veins. They typically
present with painless or painful inguinal swelling, which may be clinically mistaken
for hernia, lymphadenopathy, or abscess. USG is the imaging modality of choice and
shows the classical “bag of worms” appearance composed of multiple dilated veins along
the inguinal canal ([Fig. 14]). This can be confirmed by Doppler with augmentation by the Valsalva maneuver.[26]
[27]
Fig. 14 (A) Grayscale ultrasonography and (B) Doppler of the right groin in a second-trimester pregnant woman who presented with
palpable swelling show a clump of vessels with venous flow likely attributed to round
ligament varices.
Benign Tumors
Leiomyomas and mesothelial cysts ([Fig. 15]) are commonly reported benign masses from round ligaments. Leiomyomas are very rare
tumors of the round ligament that have a predilection for the right side extraperitoneal
location.[11]
[12] Clinically they present with inguinal or vulval masses and hence are mistaken for
incarcerated hernia. They most often show hydropic degeneration.[28] MR can depict an elongated mass along the round ligament within the inguinal canal
of in the vulva ([Fig. 16]). Heterogenous enhancement is often seen due to underlying degeneration. Surgical
excision is the treatment of choice.
Fig. 15 T2-weighted (A) sagittal, (B) coronal, and (C) axial sections show a uniloculated cystic lesion (*) with thin septations in the
supravesical region related to the left round ligament (arrows) and separate from ovaries—proven mesothelial cyst of the left round ligament.
Fig. 16 (A, B) Ultrasonography of the left inguinal region shows a heteroechoic elongated lesion
in the region of the inguinal canal (solid arrow in a) with a deep component (dotted arrow in B). (C) Coronal postcontrast maximum intensity projection image shows the origin of the
mass from the round ligament (bent arrow), which was subsequently confirmed on surgery as a round ligament fibroid with hydropic
degeneration * refers to coexisting uterine intramural fibroid. Sagittal sections:
(D) T1, (E) T2, and (F) T1 post-contrast show a dumbbell-shaped mass with partial enhancement of the hypointense
areas.
Other rare benign tumors reported in the literature include lipoma, dermoid, and serous
cystadenoma.[29]
[30]
Malignant Tumors
A PubMed search for primary malignant round ligament tumors revealed two cases of
leiomyosarcoma[31]
[32] and two cases of malignant perivascular epithelioid cell tumor (PEComa)[33]
[34] accounting for its extreme rarity. These are pathological diagnoses and imaging
features grossly overlap those of benign leiomyomas.
Secondary involvement/spread to the round ligament is known and is through one of
the pathways of uterine and ovarian lymphatic drainage along the round ligaments to
the inguinal and femoral nodes[35]
[36] ([Fig. 17]).
Fig. 17 (A) Axial, (B, C) coronal, and (D) sagittal T2-weighted images show a malignant lesion of the uterus (*) with involvement
of the bilateral round ligaments (white arrows) with right inguinal lymphadenopathy (black arrow).
Case reports of the spread of endometrial, cervical, ovarian, gastric, and gallbladder
carcinomas along the round ligament presenting with inguinal nodes are reported in
the literature requiring special attention to such occurrences that need a change
in management options and a more vigilant approach ([Fig. 18]).[37]
[38]
[39]
Fig. 18 (A, B) Contrast-enhanced computed tomography in axial section in a case of carcinoma stomach
(circle in B) with peritoneal carcinomatosis (black arrow in B) shows thickening and enhancement of bilateral round ligaments (white arrows in A) suggestive of a malignant spread.
Canal of Nuck Pathologies
The processus vaginalis gets obliterated between the eighth month of gestation and
1 year of life in the craniocaudal direction. The portion that persists within the
inguinal canal is called the “canal of Nuck.” It is related to the round ligament
anteromedially within the inguinal canal.[2]
The patent canal of Nuck can be seen as a physiological finding in infants but poses
a risk for herniation of abdominal contents. Both genital and intestinal herniation
can occur, and like any other hernia, there is a risk of obstruction or incarceration,
resulting in ischemia of the organ.
Canal of Nuck hydrocele is due to partial or complete obliteration of the processus
vaginalis and classified into three types[40] based on shape and communication ([Fig. 19]). Type 1 is common and is shaped like a sausage, round or comma shaped, or has a
“cyst in cyst” appearance. A sudden increase in size may be secondary to inflammation
and clinically present like an irreducible hernia ([Fig. 10]). Type 2 is communicating and changes in size on straining or Valsalva maneuver.
USG is the preferred modality to demonstrate the patent processus vaginalis ([Fig. 20]). Type 3 is uncommon, hourglass shaped due to compression in the center within the
inguinal canal ([Fig. 21]).
Fig. 19 Illustration of the types of canal of Nuck cysts. (A) Type 1: sausage, round, and comma shaped. (B) Type 2: tubular and cystic communicating. (C) Type 3: hourglass shaped.
Fig. 20 (A, B) Ultrasonography of the right groin in a female with intermittent swelling at different
intervals shows collapsed (arrows in A) and fluid-filled (arrows in B) elongated lesion suggestive of communicating type (type 2) of canal of Nuck hydrocele.
Fig. 21 (A) Ultrasound right inguinal region shows an elongated cystic lesion with thin septation
within. T2 weighted magnetic resonance imaging in (B) sagittal and (C) axial planes show an elongated cystic lesion with a central waist (hourglass) in
the inguinal canal (dotted arrow) suggestive of type 3 canal of Nuck hydrocele.
Hernia into the patent processus vaginalis can manifest in infancy or later age. The
hernial sac can contain the genitalia such as ovaries, fallopian tubes, and uterus
or intestines. The former is seen in infants. Isolated ovarian herniation is associated
with the MRKH syndrome ([Fig. 22]). Mullerian anomaly in the MRKH syndrome probably interferes with normal obliteration
of the processus vaginalis, resulting in ovarian descent into the inguinal canal.
Herniated ovaries can undergo torsion and ischemic infarct.[41]
[42]
[43]
Fig. 22 (A) Ultrasonography of the inguinal region shows the ovary with follicles within the
inguinal canal (white arrows) conforming to the shape of the canal. (B) Coronal computed tomography image shows bilateral ovaries within the inguinal canals.
(C, D) Magnetic resonance in axial and sagittal planes show bilateral ovaries in the inguinal
canal with an absent uterus (circle) consistent with MRKH (Mayer–Rokitansky–Kuster–Hauser) syndrome.
Conclusion
Round ligament and related pathologies are often overlooked. With the advent of cross-sectional
imaging, especially MRI, details pertaining to the round ligament involvement by various
pathologies aid in better management and outcomes.
