What is the best approach to determine ovarian laterality in a patient with a history of ovarian surgery or endometriosis?

Determining Ovarian Laterality

The most reliable method to determine ovarian laterality is transvaginal ultrasound (TVUS) combined with transabdominal ultrasound (TAUS), which allows identification of each ovary by its anatomical relationship to the internal iliac veins (posterior) and external iliac vessels (lateral), with the ovaries positioned lateral to the uterus. 1

Anatomical Landmarks for Laterality Determination

Primary Vascular Landmarks

• The ovaries are consistently located anterior to the internal iliac veins and medial to the external iliac vessels, providing the most reliable reference points for identifying right versus left ovary 1
• Each ovary should be scanned in at least two planes (short and long axis) to ensure complete visualization and accurate side identification 1
• The ovaries lie lateral to the uterus, and their position relative to the uterine midline helps confirm laterality 1

Ultrasound Technique for Laterality Assessment

Transabdominal Approach:

• Position the transducer above the symphysis pubis and examine through a bladder window 1
• To image each ovary, slide the transducer to the contralateral side and angle back toward the ovary of interest—this cross-body technique helps confirm which side you're examining 1
• The transabdominal view provides the best overview of pelvic anatomy and spatial relationships 1

Transvaginal Approach:

• After examining the uterus in sagittal and coronal planes, sweep laterally to each side to locate the ovaries 1
• The ovaries are positioned lateral to the uterus and can be identified by their relationship to the iliac vessels 1
• TVUS has superior resolution for ovarian detail but requires careful attention to probe orientation and patient positioning 1

Special Considerations in Post-Surgical or Endometriosis Patients

Challenges with Altered Anatomy

• In patients with prior ovarian surgery or endometriosis, normal anatomical relationships may be distorted by adhesions, making laterality determination more difficult 2
• Endometriomas can be identified by their characteristic homogeneous low-level or "ground glass" internal echoes with posterior acoustic enhancement, but confirming which ovary is affected requires careful vascular landmark identification 1

Critical Pitfalls to Avoid

• Do not assume ovarian position based solely on proximity to the uterus in patients with endometriosis, as adhesions can displace ovaries from their typical location 2
• In patients with history of ovarian transposition (performed before pelvic radiation), ovaries may be located in atypical positions—laterally transposed ovaries are more easily identified on imaging than medially transposed ones 3
• Always document the presence of surrounding ovarian parenchyma when identifying endometriomas to confirm you are examining ovarian tissue rather than other adnexal masses 1

Algorithmic Approach for Difficult Cases

Step 1: Begin with combined TAUS and TVUS, using the transabdominal view to establish overall pelvic anatomy and spatial orientation 1

Step 2: Identify the internal iliac veins bilaterally—the ovary on each side should be anterior to its ipsilateral internal iliac vein 1

Step 3: If ovaries cannot be definitively lateralized due to adhesions or surgical changes, obtain MRI pelvis with multiplanar imaging, which provides superior tissue contrast and can map distorted anatomy 2

Step 4: In cases where fertility preservation or surgical planning is needed, MRI is particularly valuable as it can definitively map ovarian location even in the presence of severe endometriosis or post-surgical changes 2

Documentation Requirements

• Always document which ovary (right or left) is being examined in each image 1
• Record the anatomical landmarks used to confirm laterality (relationship to iliac vessels, uterine position) 1
• In patients with endometriosis or prior surgery, explicitly note any anatomical distortion that affects confidence in laterality determination 2

When Laterality Cannot Be Determined

• If laterality remains uncertain after optimal ultrasound technique, MRI pelvis is the next appropriate step rather than proceeding with uncertain identification 2
• This is particularly important when surgical planning is involved, as operating on the wrong ovary has obvious serious consequences 1