- Email: [email protected]
Magnetic Resonance Imaging in Ovarian Masses
Review Article
MAGNETIC RESONANCE IMAGING IN OVARIAN MASSES Narayan Pendse Consultant, Department of Radiology & Imaging Sciences, Indraprastha Apollo Hospitals, Sarita Vihar, New Delhi 110 076, India. e-mail: [email protected] MR imaging has become an important tool in diagnosis, evaluation, staging and follow up of benign as well as malignant diseases of the female pelvis, infertility work up and obstetric imaging (maternal complications and fetal anomalies). Adnexal masses present a specific diagnostic challenge, and a high degree of suspicion for malignancy is critical. Due to inherent superior inter tissue contrast and ability to determine tissue type on basis of various signal intensity characteristics (“the ISSUE is TISSUE”), MRI makes possible a systematic approach to evaluate ovarian masses. Key words: Diagnosis, Magnetic resonance imaging, Ovarian mass.
INTRODUCTION
while malignant tumors do so centrally. Also malignant tumor vessels lack smooth muscle in their walls and demonstrate irregular course and arteriovenous shunts. Two common indices, pulsatility index and resistive index, increase with increasing distal vascular resistance and have a high correlation. RI less than 0.5 and PI less than 1.0 are considered suspicious for malignancy [2].
OVARIAN cancer remains the leading cause of death amongst gynecological malignancies. The degree of suspicion for malignancy in a given ovarian mass is largely based on diagnostic imaging, but correlation with other factors like CA-125 levels is useful, especially when noninvasive or minimally invasive management is being considered. A multimodality approach comprising of clinical examination, imaging and serum assays is necessary to detect malignancy at an early stage [1].
Major drawback of these modalities is operator dependence and lack of standard criteria. Also a host of conditions like physiologic alterations due to menstrual cycle and certain inflammatory conditions can lower vascular resistance and lead to erroneous interpretation.
While approaching ovarian masses, two important facts regarding CA-125 level must be borne in mind by clinicians as well as imaging experts–CA-125 is not a tumor specific antigen and may be elevated in a number of conditions (including 1% normal population) and that in follow up cases, increasing CA-125 levels are predictive of recurrence regardless of imaging findings. Also, negative serum CA-125 assay and negative imaging findings do not exclude recurrent disease [1].
Computed Tomography
IMAGING MODALITIES Ultrasonography & Color Doppler Being inexpensive, noninvasive and widely available US is at least initially the modality of choice in adnexal imaging. High frequency endovaginal probes allow markedly improved uterine and adnexal imaging. Evaluation of morphological features like wall thickness and irregularity, endopapillary projections, mural nodules etc. help distinguish benign from malignant masses. Use of color Doppler in conjunction allows in differentiating solid tumor from nonvascularized structures. Benign lesions tend to initiate neoangiogenesis peripherally Apollo Medicine, Vol. 3, No. 1, March 2006
60
Spiral CT scanning and recently the increasing availability of multidetector computed tomography (MDCT) has certain distinct advantages over all other modalities. Use of iodinated oral contrast helps reliably delineate bowel and confident differentiation with other masses, deposits and lymph nodes can be made. Also a comprehensive assessment of abdomen and pelvis for metastatic deposits and/or peritoneal implants can be made. Reduced scan time on MDCT also assures better patient compliance. Disadvantages include exposure to ionizing radiation and lack of inherent soft tissue contrast. Magnetic Resonance Imaging MRI, owing to its superior inherent soft tissue contrast and ability to reliably differentiate various tissues like fat, muscle, collagen, fibrosis, etc. is poised to become a one stop shop imaging modality for evaluation of pelvic masses, especially in cases where clinical and US findings are uncertain or equivocal. Excellent multiplanar and 3D
Review Article
reconstructions, dynamic scanning, diffusion imaging, perfusion imaging and spectroscopy are only some of the exciting new features provided by newer systems. Lack of exposure to ionizing radiation and iodinated contrast material are further advantageous over CT scanning. Though magnets from 0.2 to 3.0 Tesla are available for medical imaging, special sequences like the few mentioned above are available only with the higher strength magnets (1.5 or 3 T). Indications The American College of Radiology (ACR) has published guidelines to assist practitioners provide appropriate radiologic care for patients. It states that MRI is a proven and useful tool for evaluation, assessment and follow up of diseases of pelvic organs. Few valid medical reasons for performance of pelvic MRI include: detection and staging of gynecologic malignancies, evaluation or pelvic pain or mass, assessment of tumor recurrence, evaluation of operative complications etc. [3].
(a)
Imaging Technique The patient should have no contraindication for undergoing MRI. Due to time required for MR imaging, the patient should be able to lie flat and cooperate for approx 20 minutes. A six-hour fast helps reduce bowel peristalsis or alternatively 0.5 to 1 mg Glucagon may be administered intramuscularly. Best resolution is achieved using a multicoil array. A combination of T1, T2, Proton Density and Fat Suppressed images in axial, coronal and sagittal planes (Fig. 1 a,b,c) followed by Gadolinium enhanced routine T1 images or dynamic scanning (if available, in arterial, capillary, venous and delayed phase), are obtained. Other added options are diffusion images and MR Urography (Fig. 2), if indicated. A wide field of view coronal T2 including kidneys and at least one axial scan through the upper abdomen should be included in the study. A whole body T1 acquisition (Mobi Track or similar view) may be obtained for assessing metastases (Fig. 3).
(b)
Normal Anatomy In women of menstruating age, ovaries should be identified in virtually every case. These are ovoid structures containing high signal follicles (Fig. 4 ). In postmenopausal women, ovaries may be atrophic and identified in only 40 % cases. The uterus comprises of high T2 signal endometrium, low T2 signal junctional zone and intermediate T2 signal myometrium (Fig. 5). The junctional zone should measure no more than 11 mm. The cervix and vagina are also readily identified. Urinary bladder contains high signal urine and
(c) Fig.1. Routine planning for axial (a), coronal (b) and sagittal (c) sections. 61
Apollo Medicine, Vol. 3, No. 1, March 2006
Review Article
Fig. 2. Non contrast MR urogram. Note mild lateral displacement of lower third of right ureter (due to abscess formation, not shown).
low signal muscular wall. Pelvic side walls and levator ani show intermediate signal [4]. Identifying the signal intensity of a mass can help narrow the differential diagnosis. Several types of tissue and fluids can be readily distinguished on MRI. Cysts are hypointense on T1 and hyperintense on T2 images, while solid lesions are usually isointense and hyperintense to skeletal muscle on T1 and T2 respectively. Fat, haemorrhage and some high viscosity fluids appear hyperintense on T1 images. Fat and haemorrhage are further separable on Fat Saturation and Gradient images. Fibrosis has low or intermediate signal on T1 and low signal on T2 images.
Fig. 3. Example of a T1 weighted whole body survey.
Endometriomas Endometriotic cysts are typically seen as multiple cystic masses with high signal on T1 and very low signal on T2 images (owing to iron concentration), a combination rarely seen in other adnexal masses (Fig. 7a & b). Thick low signal intensity walls and adhesions to surrounding organs is also readily seen.
SPECIFIC DIAGNOSES Functional cysts Simple cysts appear hypointense on T1 and hyperintense on T2 images. Cyst walls are thin and clearly depicted on T2 images. Haemorrhagic cysts show intermediate to high signal on T1 and T2 images (Fig. 6). Apollo Medicine, Vol. 3, No. 1, March 2006
Non-cystic endometrial implantations are well appreciated as T2 hypointense lesions and are better 62
Review Article
Fig. 4. Thin walled left ovarian cyst appearing hyperintense on T2 fat suppressed image. Also seen is normal right ovary with few follicles.
Fig. 6. Axial T2 image shows a hyperintense right ovarian follicular cyst (*) and left ovarian haemorrhagic cyst (arrow).
appears hyperintense on T1 images and is dark on fat suppressed images (Figs. 8a & b). Chemical shift and speckling artefacts are frequently encountered and considered diagnostic. Presence of calcification can be readily identified as blooming on gradient images. Fibrotic tumors Fibromas appear predominantly hypointense on T1 and T2 images with areas of cystic / necrotic change appearing bright on T2 images. Cystadenofibromas are multilocular cystic masses with solid fibrotic components. Pedunculated/broad ligament fibroids These are solid masses showing low signal on T2 images but signal may vary according to composition (collagen, cellular or degenerating) (Fig. 5). Epithelial neoplasms These are primarily cystic (unilocular/multilocular) masses and follow signal characteristics of fluid. Malignant varieties show varying proportion of solid component (Fig. 9).
Fig. 5. Sagittal T2 image with fat suppression showing normal anatomy of uterus. Central bright endometrium surrounded by junctional zone (arrow) and myometrium. Large predominantly hyperintense mass seen in recto uterine pouch - degenerating broad ligament fibroid.
Pseudomyxoma peritoneal Peritoneal surface implants of mucinous tumors (frequently appendix, ovary and stomach) follow mucin signal pattern (hypointense on T1 and hyperintense on T2 images), though changes in signal depending relative water content can be expected.
appreciated on fat saturation images. Mature cystic teratomas MRI readily differentiates these masses as lipid content 63
Apollo Medicine, Vol. 3, No. 1, March 2006
Review Article
(a)
(b)
Fig. 7a & b. Large right endometriotic cyst appearing hyperintense on T1 and hypointense on T2 images.
(a)
(b)
Fig.8a & b. Large right ovarian dermoid appearing predominantly hyperintense on T1 images (a) and showing suppression on FS images.
Tubo-ovarian complex
SUMMARY
These are complex solid-cystic masses (Figs. 10a & b) with stranding of adjacent fat and frequently adhere to other pelvic organs.
Owing to ready availability and a high negative predictive value in experienced hands, endovaginal sonography with color Doppler is the most practical imaging modality for assessment of ovarian masses, though
Apollo Medicine, Vol. 3, No. 1, March 2006
64
Review Article
10(b)
Fig. 9. Solid left ovary with massive ascites (proven carcinoma).
discrimination) and exposure to ionizing radiation are major drawbacks. Magnetic resonance imaging (MRI) has emerged as a problem solving modality with regard to tumor characterization and staging and allows more appropriate clinical decisions to be made in selected patients with complex ovarian masses. Various study groups have reported sensitivity and specificity ranging from 95% to 100%. Ongoing research work for perfection of diffusion and perfusion MR imaging and MR spectroscopy (e.g., malignant lesions showing intense lipid peak at 1.3 ppm) promises to take MR imaging to new heights. MRI is indeed poised to become a one-stop shop in imaging of ovarian masses. REFERENCES 1. Jeong YY, Outwater EK, Kang HK. Imaging evaluation of ovarian masses. RadioGraphics 2000; 20: 14451470. 10(a) Fig. 10a & b. Coronal T2 and axial T2 SPIR images show bilateral tubo ovarian masses. Note massive dilatation of the right tube (* in (a)).
2. Stein MS, Laifer-Narin S, Johnson MB, et al. Differentiation of benign and malignant adnexal masses : relative value of gray-scale, color Doppler, and spectral Doppler sonography. Am J Roentgenol 1995; 164: 381-386.
operator dependence remains a major issue. CT helps in assessing extent of disease, but being based on a single property of X-ray attenuation (leading to poor soft tissue
3. ACR practice guideline, 2005. 4. Fielding JR. MR imaging of the female pelvis. Radiol Clin N Am 2003; 41: 179-192.
65
Apollo Medicine, Vol. 3, No. 1, March 2006
MAGNETIC RESONANCE IMAGING IN OVARIAN MASSES Narayan Pendse Consultant, Department of Radiology & Imaging Sciences, Indraprastha Apollo Hospitals, Sarita Vihar, New Delhi 110 076, India. e-mail: [email protected] MR imaging has become an important tool in diagnosis, evaluation, staging and follow up of benign as well as malignant diseases of the female pelvis, infertility work up and obstetric imaging (maternal complications and fetal anomalies). Adnexal masses present a specific diagnostic challenge, and a high degree of suspicion for malignancy is critical. Due to inherent superior inter tissue contrast and ability to determine tissue type on basis of various signal intensity characteristics (“the ISSUE is TISSUE”), MRI makes possible a systematic approach to evaluate ovarian masses. Key words: Diagnosis, Magnetic resonance imaging, Ovarian mass.
INTRODUCTION
while malignant tumors do so centrally. Also malignant tumor vessels lack smooth muscle in their walls and demonstrate irregular course and arteriovenous shunts. Two common indices, pulsatility index and resistive index, increase with increasing distal vascular resistance and have a high correlation. RI less than 0.5 and PI less than 1.0 are considered suspicious for malignancy [2].
OVARIAN cancer remains the leading cause of death amongst gynecological malignancies. The degree of suspicion for malignancy in a given ovarian mass is largely based on diagnostic imaging, but correlation with other factors like CA-125 levels is useful, especially when noninvasive or minimally invasive management is being considered. A multimodality approach comprising of clinical examination, imaging and serum assays is necessary to detect malignancy at an early stage [1].
Major drawback of these modalities is operator dependence and lack of standard criteria. Also a host of conditions like physiologic alterations due to menstrual cycle and certain inflammatory conditions can lower vascular resistance and lead to erroneous interpretation.
While approaching ovarian masses, two important facts regarding CA-125 level must be borne in mind by clinicians as well as imaging experts–CA-125 is not a tumor specific antigen and may be elevated in a number of conditions (including 1% normal population) and that in follow up cases, increasing CA-125 levels are predictive of recurrence regardless of imaging findings. Also, negative serum CA-125 assay and negative imaging findings do not exclude recurrent disease [1].
Computed Tomography
IMAGING MODALITIES Ultrasonography & Color Doppler Being inexpensive, noninvasive and widely available US is at least initially the modality of choice in adnexal imaging. High frequency endovaginal probes allow markedly improved uterine and adnexal imaging. Evaluation of morphological features like wall thickness and irregularity, endopapillary projections, mural nodules etc. help distinguish benign from malignant masses. Use of color Doppler in conjunction allows in differentiating solid tumor from nonvascularized structures. Benign lesions tend to initiate neoangiogenesis peripherally Apollo Medicine, Vol. 3, No. 1, March 2006
60
Spiral CT scanning and recently the increasing availability of multidetector computed tomography (MDCT) has certain distinct advantages over all other modalities. Use of iodinated oral contrast helps reliably delineate bowel and confident differentiation with other masses, deposits and lymph nodes can be made. Also a comprehensive assessment of abdomen and pelvis for metastatic deposits and/or peritoneal implants can be made. Reduced scan time on MDCT also assures better patient compliance. Disadvantages include exposure to ionizing radiation and lack of inherent soft tissue contrast. Magnetic Resonance Imaging MRI, owing to its superior inherent soft tissue contrast and ability to reliably differentiate various tissues like fat, muscle, collagen, fibrosis, etc. is poised to become a one stop shop imaging modality for evaluation of pelvic masses, especially in cases where clinical and US findings are uncertain or equivocal. Excellent multiplanar and 3D
Review Article
reconstructions, dynamic scanning, diffusion imaging, perfusion imaging and spectroscopy are only some of the exciting new features provided by newer systems. Lack of exposure to ionizing radiation and iodinated contrast material are further advantageous over CT scanning. Though magnets from 0.2 to 3.0 Tesla are available for medical imaging, special sequences like the few mentioned above are available only with the higher strength magnets (1.5 or 3 T). Indications The American College of Radiology (ACR) has published guidelines to assist practitioners provide appropriate radiologic care for patients. It states that MRI is a proven and useful tool for evaluation, assessment and follow up of diseases of pelvic organs. Few valid medical reasons for performance of pelvic MRI include: detection and staging of gynecologic malignancies, evaluation or pelvic pain or mass, assessment of tumor recurrence, evaluation of operative complications etc. [3].
(a)
Imaging Technique The patient should have no contraindication for undergoing MRI. Due to time required for MR imaging, the patient should be able to lie flat and cooperate for approx 20 minutes. A six-hour fast helps reduce bowel peristalsis or alternatively 0.5 to 1 mg Glucagon may be administered intramuscularly. Best resolution is achieved using a multicoil array. A combination of T1, T2, Proton Density and Fat Suppressed images in axial, coronal and sagittal planes (Fig. 1 a,b,c) followed by Gadolinium enhanced routine T1 images or dynamic scanning (if available, in arterial, capillary, venous and delayed phase), are obtained. Other added options are diffusion images and MR Urography (Fig. 2), if indicated. A wide field of view coronal T2 including kidneys and at least one axial scan through the upper abdomen should be included in the study. A whole body T1 acquisition (Mobi Track or similar view) may be obtained for assessing metastases (Fig. 3).
(b)
Normal Anatomy In women of menstruating age, ovaries should be identified in virtually every case. These are ovoid structures containing high signal follicles (Fig. 4 ). In postmenopausal women, ovaries may be atrophic and identified in only 40 % cases. The uterus comprises of high T2 signal endometrium, low T2 signal junctional zone and intermediate T2 signal myometrium (Fig. 5). The junctional zone should measure no more than 11 mm. The cervix and vagina are also readily identified. Urinary bladder contains high signal urine and
(c) Fig.1. Routine planning for axial (a), coronal (b) and sagittal (c) sections. 61
Apollo Medicine, Vol. 3, No. 1, March 2006
Review Article
Fig. 2. Non contrast MR urogram. Note mild lateral displacement of lower third of right ureter (due to abscess formation, not shown).
low signal muscular wall. Pelvic side walls and levator ani show intermediate signal [4]. Identifying the signal intensity of a mass can help narrow the differential diagnosis. Several types of tissue and fluids can be readily distinguished on MRI. Cysts are hypointense on T1 and hyperintense on T2 images, while solid lesions are usually isointense and hyperintense to skeletal muscle on T1 and T2 respectively. Fat, haemorrhage and some high viscosity fluids appear hyperintense on T1 images. Fat and haemorrhage are further separable on Fat Saturation and Gradient images. Fibrosis has low or intermediate signal on T1 and low signal on T2 images.
Fig. 3. Example of a T1 weighted whole body survey.
Endometriomas Endometriotic cysts are typically seen as multiple cystic masses with high signal on T1 and very low signal on T2 images (owing to iron concentration), a combination rarely seen in other adnexal masses (Fig. 7a & b). Thick low signal intensity walls and adhesions to surrounding organs is also readily seen.
SPECIFIC DIAGNOSES Functional cysts Simple cysts appear hypointense on T1 and hyperintense on T2 images. Cyst walls are thin and clearly depicted on T2 images. Haemorrhagic cysts show intermediate to high signal on T1 and T2 images (Fig. 6). Apollo Medicine, Vol. 3, No. 1, March 2006
Non-cystic endometrial implantations are well appreciated as T2 hypointense lesions and are better 62
Review Article
Fig. 4. Thin walled left ovarian cyst appearing hyperintense on T2 fat suppressed image. Also seen is normal right ovary with few follicles.
Fig. 6. Axial T2 image shows a hyperintense right ovarian follicular cyst (*) and left ovarian haemorrhagic cyst (arrow).
appears hyperintense on T1 images and is dark on fat suppressed images (Figs. 8a & b). Chemical shift and speckling artefacts are frequently encountered and considered diagnostic. Presence of calcification can be readily identified as blooming on gradient images. Fibrotic tumors Fibromas appear predominantly hypointense on T1 and T2 images with areas of cystic / necrotic change appearing bright on T2 images. Cystadenofibromas are multilocular cystic masses with solid fibrotic components. Pedunculated/broad ligament fibroids These are solid masses showing low signal on T2 images but signal may vary according to composition (collagen, cellular or degenerating) (Fig. 5). Epithelial neoplasms These are primarily cystic (unilocular/multilocular) masses and follow signal characteristics of fluid. Malignant varieties show varying proportion of solid component (Fig. 9).
Fig. 5. Sagittal T2 image with fat suppression showing normal anatomy of uterus. Central bright endometrium surrounded by junctional zone (arrow) and myometrium. Large predominantly hyperintense mass seen in recto uterine pouch - degenerating broad ligament fibroid.
Pseudomyxoma peritoneal Peritoneal surface implants of mucinous tumors (frequently appendix, ovary and stomach) follow mucin signal pattern (hypointense on T1 and hyperintense on T2 images), though changes in signal depending relative water content can be expected.
appreciated on fat saturation images. Mature cystic teratomas MRI readily differentiates these masses as lipid content 63
Apollo Medicine, Vol. 3, No. 1, March 2006
Review Article
(a)
(b)
Fig. 7a & b. Large right endometriotic cyst appearing hyperintense on T1 and hypointense on T2 images.
(a)
(b)
Fig.8a & b. Large right ovarian dermoid appearing predominantly hyperintense on T1 images (a) and showing suppression on FS images.
Tubo-ovarian complex
SUMMARY
These are complex solid-cystic masses (Figs. 10a & b) with stranding of adjacent fat and frequently adhere to other pelvic organs.
Owing to ready availability and a high negative predictive value in experienced hands, endovaginal sonography with color Doppler is the most practical imaging modality for assessment of ovarian masses, though
Apollo Medicine, Vol. 3, No. 1, March 2006
64
Review Article
10(b)
Fig. 9. Solid left ovary with massive ascites (proven carcinoma).
discrimination) and exposure to ionizing radiation are major drawbacks. Magnetic resonance imaging (MRI) has emerged as a problem solving modality with regard to tumor characterization and staging and allows more appropriate clinical decisions to be made in selected patients with complex ovarian masses. Various study groups have reported sensitivity and specificity ranging from 95% to 100%. Ongoing research work for perfection of diffusion and perfusion MR imaging and MR spectroscopy (e.g., malignant lesions showing intense lipid peak at 1.3 ppm) promises to take MR imaging to new heights. MRI is indeed poised to become a one-stop shop in imaging of ovarian masses. REFERENCES 1. Jeong YY, Outwater EK, Kang HK. Imaging evaluation of ovarian masses. RadioGraphics 2000; 20: 14451470. 10(a) Fig. 10a & b. Coronal T2 and axial T2 SPIR images show bilateral tubo ovarian masses. Note massive dilatation of the right tube (* in (a)).
2. Stein MS, Laifer-Narin S, Johnson MB, et al. Differentiation of benign and malignant adnexal masses : relative value of gray-scale, color Doppler, and spectral Doppler sonography. Am J Roentgenol 1995; 164: 381-386.
operator dependence remains a major issue. CT helps in assessing extent of disease, but being based on a single property of X-ray attenuation (leading to poor soft tissue
3. ACR practice guideline, 2005. 4. Fielding JR. MR imaging of the female pelvis. Radiol Clin N Am 2003; 41: 179-192.
65
Apollo Medicine, Vol. 3, No. 1, March 2006