Tarlov Cysts Mimicking Adnexal Masses: Two Case Reports

: Tarlov cysts are cystic structures of neurogenic origin that arise most commonly in the roots of the sacrococcygeal nerves. Prompt and correct identification can prevent unnecessary biopsy of the cysts, a procedure which can cause significant pain because they contain nerve fibers and ganglion cells. We report two cases of Tarlov cysts mimicking adnexal masses on ultrasound evaluation. The first case was misidentified on an ultrasound before being diagnosed as a Tarlov cyst during follow-up magnetic resonance imaging. The second case was initially identified by the sonographer as an ovarian cyst but was properly identified through correlation with prior computed tomography imaging. In this case series, we discuss the pathologic and radiographic features, etiology, clinical considerations, and treatment of Tarlov cysts.


Case 2 Presentation
A 50-year-old woman presented to the emergency department for acute pain in the left lower quadrant of her abdomen.Computed tomography (CT) of the abdomen and pelvis showed acute uncomplicated diverticulitis, a 1.8 cm cystic lesion in the left adnexa (not shown), and bilateral sacral Tarlov cysts (Figure 3).The patient was treated conservatively with a course of amoxicillinclavulanate for the diverticulitis and was discharged.
A pelvic ultrasound ordered one year later to evaluate the patient for the presence of uterine fibroids showed resolution of the left ovarian cyst, but a right-sided cystic structure was visualized (Figure 4).The cystic structure was initially identified by the sonographer as a right ovarian cyst, but a review of prior imaging by the A Abstract: Tarlov cysts are cystic structures of neurogenic origin that arise most commonly in the roots of the sacrococcygeal nerves.Prompt and correct identification can prevent unnecessary biopsy of the cysts, a procedure which can cause significant pain because they contain nerve fibers and ganglion cells.We report two cases of Tarlov cysts mimicking adnexal masses on ultrasound evaluation.The first case was misidentified on an ultrasound before being diagnosed as a Tarlov cyst during follow-up magnetic resonance imaging.The second case was initially identified by the sonographer as an ovarian cyst but was properly identified through correlation with prior computed tomography imaging.In this case series, we discuss the pathologic and radiographic features, etiology, clinical considerations, and treatment of Tarlov cysts.

Key Points
▪ Tarlov cysts are sacrococcygeal cystic structures of neurogenic origin that contain nerve fibers and ganglion cells.▪ Tarlov cysts are situated in the posterior pelvis and originate from the sacrum, which may predispose them to misidentification as adnexal masses on ultrasound.▪ Familiarity with the relevant imaging features of Tarlov cysts may allow for accurate diagnosis and prevent unnecessary follow-up imaging or biopsy.
interpreting radiologist allowed for the correct identification of the cyst in question as the previously identified right-sided Tarlov cyst.

Pathology and Radiographic Features
Tarlov cysts, also known as meningeal cysts or perineural cysts, are neurogenic cysts that contain cerebrospinal fluid, extensive fibrotic elements, and, in some cases, evidence of old hemorrhage on histopathologic examination. 1 As type II spinal meningeal cysts, 1-3 they are differentiated from other spinal meningeal cysts, such as meningoceles and arachnoid cysts, by the fact that they are extradural and contain spinal nerve root fibers.Tarlov cysts can arise between the pia and arachnoid at the junction of the dorsal root ganglion and spinal nerve root and have been reported to most commonly occur at the second and third sacral nerve root levels. 4,5Posteriorly  Tarlov cysts may form unilaterally or bilaterally and can be seen as unilocular or multilocular cystic masses.They may also contain delicate, thin septations. 9In the cases presented in this report, thin septations within the Tarlov cysts were best seen on ultrasound rather than on MRI due to the higher spatial resolution of ultrasound for the targeted evaluation of cystic structures.

Etiology
The mechanism of Tarlov cyst formation is unclear, but Tarlov proposed that these cysts were sequelae of post-traumatic hemorrhage. 10It has also been proposed that Tarlov cysts are congenital in origin. 5,9Others propose that stenosis of the ostium of the nerve root results in a ball-valve effect in which cerebrospinal fluid enters the cysts through systolic pulsations but is unable to exit. 5,9,10

Clinical Considerations and Treatment
Tarlov cysts are most commonly discovered incidentally during MRI performed for lower back pain, which is typically resolved by the treatment of a spinal abnormality independent of the Tarlov cyst. 6,7,9The prevalence of Tarlov cysts during lumbosacral MRI has been estimated to be 4.6%, which has been extrapolated to represent the prevalence in the general adult population. 5,8etropelvic cysts identified on ultrasound should be followed up with MRI to identify possible Tarlov cysts. 1 Tarlov cysts may rarely cause pelvic symptoms such as abdominal or pelvic pain, lower back pain, or bowel or genitourinary dysfunction.Mild symptoms may be managed conservatively with anti-inflammatory drugs.In the instance that a cyst causes significant symptoms, however, surgical interventions such as cyst ablation or excision may be considered. 1,7,8In both cases discussed here, the Tarlov cysts caused no symptoms, and no treatment was pursued.
Tarlov cysts identified on pelvic ultrasound may be mistaken for adnexal masses, so awareness of the imaging features of Tarlov cysts can assist in accurate diagnosis and avoidance of unnecessary biopsy, which can cause painful neuropathic symptoms. 1,7,9Comparison with prior crosssectional imaging allowed the image reader to correctly identify a Tarlov cyst in one of the two cases discussed.
Contrast-enhanced CT of the pelvis shows bilateral sacral Tarlov cysts (red arrows), with the right-sided cyst measuring 4.1 cm.

Conclusion
We report two cases of Tarlov cysts mimicking adnexal masses on ultrasound, and which were subsequently confirmed primarily by crosssectional imaging.Due to a Tarlov cyst's sacral origin and its usual lack of associated symptoms, it is likely to be misdiagnosed as an adnexal mass.Avoiding misdiagnosis may be possible by identifying the Tarlov cyst's sacral foraminal origin on ultrasound or by correlation with crosssectional imaging.

Figure 1 .
Figure 1.Ultrasound Images of the Right Adnexa of a 47-Year-Old Woman with a Tarlov Cyst.

Figure 2 .
Figure 2. MRI of the Pelvis of a 47-Year-Old Woman with a Tarlov Cyst.

Figure 3 .
Figure 3. Contrast-Enhanced CT of the Pelvis of a 50-Year-Old Woman with Bilateral Tarlov Cysts, Axial View.

Figure 4 .
Figure 4. Color Doppler Ultrasound of the Pelvis of a 50-Year-Old Woman with a Tarlov Cyst.