AJR 2001; 177:1313-1318
© American Roentgen Ray Society
Perineural Cysts Presenting as Complex Adnexal Cystic Masses on Transvaginal Sonography
Mark J. McClure1,2,
Mostafa Atri1,
Masoom A. Haider3 and
John Murphy1
1
Department of Medical Imaging, Sunnybrook & Women's Health Science Centre,
2075 Bayview Ave., Ontario, M4N 3M5 Canada.
2
Present address: Department of Radiology, Craigavon Area Hospital, 68 Lurgan
Rd., Portadown Craigavon, BT63 5QQ Northern Ireland.
3
Department of Medical Imaging, Mount Sinai Hospital and University Health
Network, 600 University Ave., Toronto, Ontario, M5G 1X5 Canada.
Received September 20, 2000;
accepted after revision June 25, 2001.
Address correspondence to M. J. McClure.
Abstract
OBJECTIVE. This study describes the sonographic features of sacral
perineural cysts that initially presented as adnexal complex cystic masses on
transvaginal sonography.
CONCLUSION. Perineural cysts may have a complex cystic appearance,
including septation and internal debris, on transvaginal sonography. The
extraovarian, extraperitoneal, and posterior location on real-time sonography
are suggestive features.
Introduction
Transvaginal sonography is a frequently performed examination for the
evaluation of adnexal masses. Sonography confirms the location of these masses
in relation to the ovary, the cystic or solid nature of such lesions, and
further characterizes complexity such as wall thickening or nodulation,
septation, internal debris, and vascularity. Causes of complex adnexal cysts
include ovarian cystic benign and malignant tumors, functional ovarian masses,
endometriomas, and extraovarian lesions such as fallopian tube related masses,
paraovarian cysts, abscesses, hematomas, and lymph nodes. With extraovarian
lesions, the ovaries should be identified as separate structures.
Identification of perineural cysts is more frequent with the increasing use
of MR imaging of the pelvis and lumbosacral spine
[1,2,3].
The MR signal characteristics and multiplanar capability readily show the
cystic nature of these lesions and their origin from the sacral foramina. We
describe transvaginal sonographic features of this condition with CT and MR
correlation.
Materials and Methods
This series consists of five women (age range, 28-44 years; mean age, 39.6
years) presenting with adnexal complex cystic masses identified on
transvaginal sonography over one year. Patients were referred for
investigation of pelvic pain (n = 4), dysmenorrhea (n = 2),
dyspareunia (n = 1), and perineal pain (n = 1). All patients
(n = 5) were examined by transvaginal sonography followed by MR
imaging (pelvis, n = 4; lumbosacral spine, n = 1). Two
patients also underwent a CT examination before MR imaging. MR imaging was
performed for further assessment of these lesions because of its known role in
further characterizing and localizing nonspecific adnexal masses seen on
transvaginal sonography [4,
5]. We used MR imaging to
document the final diagnosis in these cases.
Sonographic images were obtained with an HDI 5000 scanner (Advanced
Technology Laboratories, Bothwell, WA). Transabdominal sonography using curved
array transducers with a frequency of 3 or 5 MHz was performed on all patients
(n = 5), followed by transvaginal sonography with a transducer
frequency range of 4 to 8 MHz. The examinations included assessment of
gray-scale and color Doppler sonography in all five patients.
Contrast-enhanced helical CT was performed on a HiSpeed Advantage scanner
(General Electric Medical Systems, Milwaukee, WI), with a slice collimation of
8 mm performed after administration of 150 mL of iodinated IV contrast
material at 3 mL/sec. Pelvic MR imaging (n = 4) was performed with a
1.5-T GE scanner (Horizon LX; General Electric Medical Systems) using a torso
coil. Four patients underwent axial T1-weighted spin-echo sequences (TR/TE,
650/10; slice thickness, 8 mm) and axial and coronal T2-weighted fast
spin-echo sequences (6200/100; slice thickness, 4 mm). A contrast-enhanced
T1-weighted spoiled gradient-echo sequence (6.1/1.4; slice thickness, 5 mm)
was also performed on two of the four patients after a bolus IV injection of
0.1 mmol/kg of gadolinium dimeglumine (Magnevist; Berlex Canada, Montreal,
Canada). Lumbosacral spine MR imaging using a phased-array surface coil was
performed on one patient. Sagittal T1-weighted spin-echo sequence (360/20;
slice thickness, 3 mm) and sagittal and oblique coronal T2-weighted fast
spin-echo sequences (4000/80; slice thickness, 3 mm) were performed.
Results
Normal-appearing ovaries were identified as separate structures in all
patients (Fig.
1A,1B,1C).
All cystic masses (n = 8) were identified posteriorly in relation to
the ovaries and located anteriorly to the sacrum (Figs.
1A,1B,1C,2A,2B,3A,3B,4A,4B,4C,5A,5B,5C).
Three cases were bilateral (Figs.
1A,1B,1C,
4A,4B,4C,
and
5A,5B,5C)
and two were unilateral (Figs.
2A,2B
and
3A,3B).
The lesions were multilocular (n = 7, three bilateral and one
unilateral left-sided) and unilocular (n = 1, unilateral left-sided).
The number of locules per lesion ranged from one to seven (mean, 4.5). The
largest locule size ranged from 21 to 33 mm (mean, 26 mm). Wall thickness was
uniformly thin (<2 mm) in all cysts, with no mural nodularity identified.
Septa were identified in three patients (Figs.
2A,2B,3A,3B,4A,4B,4C)
and were uniformly thin (<2 mm), with no septal nodularity. All patients
contained internal debris in at least one locule, which was floating
(n = 4), layered (n = 4), and heterogenous (n = 1).
Color Doppler sonography revealed no vascularity in any lesion.
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Fig. 1A. —42-year-old woman with perineal pain and bowel disturbance.
Sagittal transvaginal sonogram of right adnexa shows complex cystic mass
(white arrows) containing heterogenous internal debris. Mass is
clearly separate from right ovary (RO) and posteriorly located anterior to
sacrum (black arrow). Multiocular cystic lesion was also identified
in left adnexa (not shown).
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Fig. 1B. —42-year-old woman with perineal pain and bowel disturbance.
Transverse transvaginal sonogram of right adnexa shows absence of detectable
blood flow on color Doppler sonography. Some internal debris is seen layered
dependently with change in patient's position.
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Fig. 1C. —42-year-old woman with perineal pain and bowel disturbance.
Axial T2-weighted MR image shows bilateral hyperintense multilocular cysts
(arrows). Note uniformly thin walls and absence of septa.
Heterogenous signal intensity of right-sided lesions correlates with
heterogenous debris seen on transvaginal sonography.
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Fig. 2A. —43-year-old woman with left lower quadrant pain and
dysmenorrhea. Sagittal transvaginal sonogram of left adnexa shows complex
cystic mass containing thin (<2 mm) septation (curved arrow) and
fine internal floating debris with dependent layering (white straight
arrow). Lesion is posteriorly located on sacrum (black
arrow).
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Fig. 2B. —43-year-old woman with left lower quadrant pain and
dysmenorrhea. Axial T2-weighted MR image shows hyperintense fluid in
unilocular cyst that contains layering internal debris (arrow).
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Fig. 3A. —28-year-old woman with persistent pelvic pain, dysmenorrhea,
and dyspareunia. Transverse transvaginal sonogram of left adnexa shows complex
cyst containing several thin (<2 mm) septa (curved arrow), with
some floating and layered internal debris (straight solid arrow)
located posteriorly adjacent to sacrum (open arrow).
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Fig. 3B. —28-year-old woman with persistent pelvic pain, dysmenorrhea,
and dyspareunia. Axial T2-weighted MR image shows multilocular left-sided
cysts. Location of these cysts abutting left piriformis muscle (P) may help
explain initial consideration of piriformis muscle hematoma in differential
diagnosis based on transvaginal sonographic appearance.
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Fig. 4A. —41-year-woman with 2-month history of pelvic pain. Sagittal
transvaginal sonogram of right adnexa shows complex multilocular cystic mass
containing few thin (<2 mm) septations (curved arrow) and floating
and layered internal debris (white arrow). Lesions are located
posteriorly on sacrum (black arrow). Note presence of free fluid
(FF).
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Fig. 5A. —44-year-old woman with lower abdominal pain. Transverse
transvaginal sonogram of left adnexa shows complex tubular-shaped cystic
lesion (small white dots) containing internal floating (white
arrow) and layered (asterisk) echogenic debris. Dorsal location
is evident by sacrum (black arrow).
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The initial differential diagnostic considerations, based on the
sonographic features, included endometrioma (n = 3), tubo-ovarian
abscess (n = 1), internal iliac lymphadenopathy (n = 1),
hydrosalpinx (n = 1), piriformis muscle hematoma (n = 1),
and ectopic pregnancy (n = 1). The patient with the largest lesion
(Fig.
1A,1B,1C),
and who complained of perineal pain, was undergoing treatment for anal
fissures and irritable bowel syndrome that were thought to contribute to her
symptoms. One patient (Fig.
2A,2B)
had laparoscopic confirmation of extraovarian endometriosis and transvaginal
sonography of the previous year for comparison, which remained unchanged. A
hematoma was considered in one patient, given the location to the ipsilateral
piriformis muscle (Fig.
3A,3B).
In another patient, the adnexal cystic mass was associated with free pelvic
fluid (Fig. 4A), and ectopic
pregnancy was considered. A subsequent test for pregnancy was negative.
CT (n = 2) (Figs.
4A,4B,4C
and
5A,5B,5C)
showed the lesions to be of uniform water attenuation (<10 H), located
anterior to the sacrum, and with widened sacral foramina. MR imaging
(n = 5) confirmed the presence of perineural cysts, and multiplanar
acquisition helped to show ventral herniation through the sacral foramina and
connection with the thecal sac. All perineural cysts were of high signal
intensity on T2-weighted sequences and of low signal intensity on T1-weighted
sequences. A heterogeneous high signal intensity on T2-weighted sequences in
some lesions (Fig. 1C) correlated with the internal debris seen on transvaginal sonography
(Fig. 1A). No wall or septal
thickening was seen in any lesion, and no enhancement of the wall was present
on CT or MR imaging.
Discussion
Perineural cysts are relatively common. Tarlov
[6] originally described five
cases in 1938 as incidental findings during autopsies of 30 adults. More
recently, Paulsen et al. [3]
reported 23 cases of perineural cysts in 500 sequential lumbosacral MR
examinations. Usually, the perineural cysts are located in the lower lumbar
and sacral spinal canal and may extend through adjacent foramina with
associated bony erosion [7]. It
is unusual to identify these lesions in the pelvis by ventral extension
through the anterior sacral foramina. To our knowledge, we report the first
series in the radiology literature on sacral perineural cysts presenting as
adnexal complex cystic masses on transvaginal sonography.
In two patients, extraovarian endometrioma was considered in the
differential diagnosis on sonographic appearance, with a history of surgically
confirmed endometriosis in one patient. The third patient was unusual in that
her cystic mass appeared to be located in the left piriformis muscle, with
associated muscular pressure atrophy. On real-time examination, these masses
appeared to be fixed to the pelvic side wall, as indicated by lack of movement
during breathing. The differential diagnosis included a muscle hematoma.
Atrophy of muscle associated with pressure from a perineural cyst is evident
on MR imaging (Fig. 3B), is
previously unreported, and may be a causative factor in producing pain. The
fourth patient showed bilateral cystic adnexal lesions, and although
tubo-ovarian abscess and endometrioma were considered, the free fluid
suggested the possibility of ectopic pregnancy. In the fifth patient, the
unusual tubular configuration of the lesions suggested hydrosalpinx or
internal iliac lymphadenopathy.
The cause of perineural cysts remains uncertain. Tarlov
[8] proposed that they were
related to trauma, with hemorrhage causing impedance of venous drainage and
subsequent rupture. Others believe they are of congenital origin
[9]. The cyst cavity is
anatomically located between the perineurium (nerve root arachnoid covering)
and the endoneurium (pial layer) and communicates with the subarachnoid space
[10]. The cyst wall usually
contains nerve fibers. Tarlov
[10] described the pathologic
finding of frequent multilocularity of lesions in surgically resected cases.
The sonographic multilocularity of the lesions that we describe correlates
well with this finding. The presence of internal septa on transvaginal
sonography and MR imaging, internal debris on transvaginal sonography, and
corresponding heterogeneous T2-weighted MR signal may represent the presence
of blood or cells and might support the traumatic etiology proposed by Tarlov
[8]. We propose that a further
possible cause for pain may be the stretching of nerve fibers contained in the
cyst wall. Alternatively, superimposed bleeding may be the cause of pain in an
otherwise asymptomatic cyst.
On the basis of the sonographic features of these five patients, we believe
that perineural cysts should be considered in the presence of an extraovarian
adnexal cystic mass that is posteriorly located and does not move with
breathing. The most common extraovarian adnexal cystic masses are
hydrosalpinges and paraovarian cysts. Although these lesions could be fixed as
a result of the associated adhesions, they are often mobile because of their
intraperitoneal location. Most hydrosalpinges are more elongated and tubular
than those in the cases we have described. Although an endometriotic cyst with
adhesion is a possibility, extraovarian endometriosis is rarely cystic and, in
general, does not reach large proportions.
The five patients we describe are interesting in that they presented
initially with lower abdominal and pelvic pain. To our knowledge, no previous
reports exist in the literature of pelvic adnexal perineural cysts causing
pain. It is uncertain if the pain described by these patients was in fact
related to the presence of the perineural cysts. One patient had
histologically proven endometriosis and another patient had a long history of
irritable bowel syndrome. These conditions certainly could play a role in
their symptomatology. The other three patients had no relevant medical history
and a relatively short duration of symptoms. It is unlikely that the cysts we
describe caused pain by pressure on adjacent structures or local nerve
stretching as a result of the short duration of symptoms and absence of low
back pain, sciatica, or urinary disturbance. Hemorrhage into an otherwise
asymptomatic cyst is possible based on the sonographic evidence. Raza et al.
[11] reported a case of
bilateral adnexal perineural cysts that were discovered during a routine
sonogram in a patient experiencing no pain. In a retrospective series by
Paulsen et al. [3], five of 23
patients with perineural cysts experienced low back pain that they attributed
to presence of the cyst, but these cysts were all located in the more typical
dorsal sacral location.
Current treatment options for symptomatic perineural cysts involve
extensive surgery with sacral laminectomy and cyst excision
[10] or, more recently,
microsurgical cyst fenestration and imbrication
[12]. Paulsen et al.
[3] described a method of
CT-guided percutaneous cyst aspiration in five women with painful
radiculopathy, but cyst fluid reaccumulated in four of the five patients. The
authors advocated this method for attaining a pain-free interval in
symptomatic patients. On the basis of our experience with transvaginal
sonography of perineural cysts, transvaginal sonographically guided aspiration
of symptomatic cysts could offer an alternative technique that would be
simple, quick, and safe to perform. The proximity of the needle-guide to the
cyst and the real-time imaging would offer advantages, although further
studies would be required to further evaluate these procedures.
Limitations of our study are the relatively small sample size and the lack
of pathologic correlation. A possible bias in the study group is the complex
nature of the masses that lead to further appropriate investigation. It is
conceivable that perineural cysts could present as simple adnexal cysts on
transvaginal sonography. On the basis of the MR imaging experience and data,
we believe that the adnexal cystic appearance of perineural cysts will be more
commonly recognized in the future, and the appearance could potentially be
less complicated than described in this series.
In conclusion, if an adnexal extraovarian cystic mass is identified on
transvaginal sonography, unilateral or bilateral, the differential diagnosis
should include perineural cyst, especially if the posterior extraperitoneal
location of the mass is suggested on realtime sonography. This finding is
important because the correct diagnosis is often reassuring for the patient
and may prevent unnecessary surgery.
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Abstract
Introduction
