Diagnostic ultrasonography should be the first examination performed; typically, the affected ovary is enlarged, with multiple immature or small follicles along its periphery.
Ultrasonography with color Doppler analysis is the method of choice for the evaluation of adnexal torsion because it can show morphologic and physiologic changes in the ovary and can help in determining whether blood flow is impaired. [12, 14, 15, 16] . Gray-scale and spectral findings are correlated with the age of the torsion (ie, acute torsion or chronic torsion) and the degree of the twist or torsion. Normal Doppler imaging must not, however, be used as a basis for excluding the diagnosis.
Rarely, computed tomography (CT) or magnetic resonance imaging (MRI) is needed to make a definitive diagnosis. CT or MRI can serve as a secondary modality when ultrasonographic findings are nondiagnostic. [17, 18, 19]
Culdocentesis is a nonspecific test that is unlikely to confirm or exclude torsion and therefore is not recommended in the diagnostic workup.
Findings indicative of torsion
Ovarian enlargement secondary to impaired venous and lymphatic drainage is the most common sonographic finding in ovarian torsion. A coexistent mass is often seen. The ovary usually contains several cysts along its periphery; these are follicles that have likely been displaced peripherally because of ovarian edema and venous congestion. In addition, there may be irregular echogenic areas within the ovary corresponding to stromal edema and/or hemorrhage.
Color Doppler sonography may be helpful in predicting viability of adnexal structures by depicting blood flow within the twisted vascular pedicle and presence of central venous flow.  On color Doppler sonograms, little or no intraovarian venous flow is present; this finding is followed by a lack of intraovarian arterial flow. Flow within the adnexal vessels may be preserved (see the video below). 
Occasionally, the twisted pedicle of the affected ovary can be recognized. A twisted pedicle is a relatively specific sign for ovarian torsion. With isolated tubal torsion, the tube is usually distended and lacks flow or has reversed flow during diastole. Because venous flow is under low pressure, it is the first flow to be affected by the increased interstitial pressure of a twisted ovary. In chronic torsion, arterial waveforms can mimic venous waveforms. When torsion is complete, no arterial waveforms can be detected within the ovary.
Intraperitoneal fluid may surround the twisted ovary. This usually is the result of interstitial fluid that weeps off an affected ovary rather than a true rupture of the capsule and extrusion of blood. [11, 12, 14, 15, 16]
The finding of an ovarian mass may suggest a focus for torsion but may also be misleading as to this is itself the source of pain. Because implicated masses are most frequently nonneoplastic or hemorrhagic cysts, which can themselves produce pain of similar quality and location, diagnosis can be challenging even with appropriate imaging. Nevertheless, when the history is suggestive of torsion, the discovery of an ovarian cyst should greatly increase one’s suspicion of the diagnosis.
Auslender et al suggested a classification of severity of adnexal torsion and treatment strategy that was based on blood flow as depicted on Doppler ultrasonography.  In their small study (n=17), they used Doppler and gray-scale ultrasonography to visualize coiling of the ovarian vessels, concluding that when coiling of the ovarian vessels is present, Doppler flow examination of the ovary can help differentiate between ischemic adnexal torsion and coiling of the ovarian blood vessels without strangulation, thus facilitating the choice of treatment. 
In 9 of these 17 patients, arterial and venous blood flow was present within the ovary, and ultrasonographic and surgical findings usually demonstrated normal-sized or mildly enlarged ovaries; in 5, only arterial blood flow was detected within the ovary, and surgery usually revealed enlarged ovaries with normal color or mild discoloration; and in 3, neither arterial nor venous blood flow was seen within the ovary, vessel coiling was evident only on gray-scale and not on Doppler examination, and signs of ovarian ischemia or necrosis were found at surgery. 
In a study of 39 patients by Shadinger et al, ovarian enlargement and the absence of ovarian venous Doppler flow were the most frequent sonographic indications of ovarian torsion. Frequent clinical symptoms included abdominal pain and vomiting. The authors concluded that ovarian torsion should be strongly suspected in the presence of ovarian enlargement and clinical symptoms, even if arterial and venous Doppler flow are present. 
Diagnostic reliability and limitations
Combining Doppler flow imaging with morphologic assessment of the ovary may improve diagnostic accuracy. However, the interpretation of Doppler sonography is inconsistent as a consequence of the dual ovarian blood supply from the uterine artery and the ovarian artery.
A small study in a specialized ultrasound unit found 74.6% accuracy when using sonography to diagnose ovarian torsion. The most diagnostically accurate sonographic signs were abnormal ovarian blood flow and the presence of free fluid. The authors cautioned that ovarian torsion should not be ruled out when typical indicators are absent, especially when clinical history is suggestive of the condition. 
The presence of an enlarged ovary with lack of intraovarian arterial or venous flow is highly indicative of torsion, particularly if the typical appearance of an enlarged ovary with small peripheral cysts is depicted. [12, 15] However, the presence of adnexal flow should not be construed as ruling out the diagnosis.
Early in the progression of disease, arterial perfusion may be preserved, with only venous and lymphatic flow obstructed. Additionally, if the scan is performed during a transient period of detorsion of the ovary, a normal Doppler flow may falsely suggest a normal ovary.
Although a lack of intraovarian arterial and venous flow enables confident diagnosis, adnexal torsion (ovarian torsion) may be incomplete; incomplete torsion may be associated with adnexal flow, as depicted with color Doppler sonography. Rarely, the use of improper settings can cause erroneous findings of absent flow. Check that the proper settings are used by looking for flow in the internal iliac vein.
In some cases, flow depiction may be difficult to obtain from the affected ovary, as well as the healthy contralateral ovary. In these cases, the characteristic gray-scale morphologic image of ovarian torsion alone may help in making the diagnosis.
Chronic tuboovarian abscesses and/or complexes may mimic torsion, particularly torsion with contained areas of infarction.
Enlarged adnexal structure (>5cm)
Thick, straight blood vessels draped around the lesion
Complete absence of enhancement
Hemorrhage or gas in the torsed lesion
Misplacement of the torsed structure (to the midline or contralateral side)
Deviation of the uterus to the involved side
Infiltration of the periadnexal fat
Thickened vascular pedical with engorged vessels
In a study by Moore et al, before undergoing surgery for ovarian torsion, 28 of 28 patients had had CT confirmation of an enlarged ovary, ovarian cyst, or adnexal mass of the involved ovary  ; the authors therefore concluded that ovarian torsion can be ruled out by well-visualized normal-appearing ovaries on CT and that either abnormal findings or inability to visualize the ovaries on CT necessitates further evaluation for possible ovarian torsion.
Although CT may demonstrate an enlarged ovary and adnexal masses, it is unable to evaluate the presence or absence of blood flow to the involved ovary. In cases of diagnostic uncertainty, however, CT may be useful in ruling out other possible causes of lower abdominal pain.  Additionally, CT can exclude the presence of a pelvic mass, thereby greatly enhancing the clinician’s ability to rule out torsion.
In a study of women who presented to the ED and were evaluated for ovarian torsion, the negative predictive value of a negative CT examination was 100%. It was also found that color Doppler ultrasound offered no utility in evaluating for ovarian torsion after a negative contrast-enhanced CT scan of the abdomen and pelvis. 
Magnetic Resonance Imaging
MRI may demonstrate ovarian enlargement and intraperitoneal fluid. In a case report, MRI demonstrated a twisted pedicle. If hemorrhagic infarction is present, MRI can demonstrate an enlarged ovary with displaced follicles. T2-weighted images show low signal intensity caused by interstitial hemorrhage, and T1-weighted images show a thin rim of high signal intensity without contrast enhancement. [17, 19, 30, 31]
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