Junctional Zone

The Common Vein

Definition

The junctional zone is subendometrial smooth muscle that is more compacted, and contains less water in comparison to the outer myometrium. (McCarthy)

The Junctional Zone – MRI

The normal sagittal view of the uterus is a T2 weighted MRI from a 16 year old female with pelvic pain. It demonstrates theta the uterus and more specifically the myometrium is more complex and consists of an outer part (dark red) and an inner more homogeneous part called the junctional zone Since a T2 weighted image is sensitive to water we understand from this image that the outer part since it has greater white signal contains more water, and likely more vascularity. The endometrial canal, cervical canal and vaginal cavity are outlined in yellow and the vaginal wall is pink.

The junctional zone is also functionally different from the outer myometrium. For example myometrial contractions in a non-pregnant woman originate exclusively from the junctional zone. The amplitude, frequency, and direction depend on the phase of the menstrual cycle.

The Uterus in the Sagittal Plane

The sagittal STIR sequence from an MRI study shows the normal appearance of the uterus in a 34 year old female. The pear shaped form is exemplified together with the 3 parts of the uterus. The inner endometrium of intermediate signal, the junctional zone of low signal consisting of compacted smooth muscle with low water content, and the surrounding myometrium of smooth muscle with a higher water content.

Axial Plane Coronal Projection

The axial STIR sequence from an MRI study shows the normal appearance of the uterus in a 34 year old female. Because the uterus is anteverted it lies flat so that in this instance the coronal plane of the uterus is demonstrated. The pear shaped form is exemplified together with the 3 parts of the uterus. The inner endometrium of intermediate signal, the junctional zone of low signal consisting of compacted smooth muscle with low water content, and the surrounding myometrium of smooth muscle with a higher water content. Two high signal cuysts are seen in the right ovary

Junctional Zone In Early Proliferative Phase

The normal sagittal view of the uterus is a transvaginal ultrasound, in the first week after menstruation after menstruation, and just prior to the next menstruation after the endometrium has been shed. It demonstrates that the endometrium becomes a single echogenic line consisting of opposing walls (orange) and is surrounded by a subendometrial halo of the junctional zone (tan). This layer is more compacted, and relatively hypovascular. This image is typical of the early proliferative phase. It is during this time that estrogen starts to rise and progesterone has fallen. The endometrium in this case measures about 3mms.

Junctional Zone in the Premenstrual Uterus

LMP 4 Weeks Prior

In this 26 year premenstrual female a transvaginal ultrasound in the sagittal plane reveals a normal view of the uterus with characteristic premenstrual appearance. (a) The stripe is almost homogeneously echogenic and thick but also shows a hypoechoic halo of the junctional zone or inner myometrium. (salmon) The homogeneous stripe is made up from two histological layers (barely distinguished by this ultrasound)– the inner stratum functionalis (deep orange) that will shed once the spiral arteries vasoconstrict, and the outer stratum basalis (deep yellow) that will not shed, and will be the basis for regenerating the endometrium in the next cycle. The next layer as stated above is the compact myometrium – the junctional zone (aka inner myometrium) , and is followed by the thicker outer myometrium (maroon). (b)

Junctional Zone During Pregnancy

The junctional zone becomes disrupted increases in intensity and zonal differences become indistinct and returns to normal 6 months after deliver Willms AB Brown ED Keittritz UIRadiology 195 91-94 1995

Junctional Zone – Early Pregnancy

In this 16 year old patient her LMP was about 4 weeks ago and she had a positive pregnancy test. The transvaginal ultrasound in the sagittal plane reveals a normal view of the uterus with characteristic early pregnancy appearance characterized by the gestational sac (gs) embedded in the stratum functionalis (deep orange). The stratum basalis is seen as a slightly more echogenic layer around the functional layer (deep yellow). The stripe is thick measuring about The next layer is a barely seen junctional layer (salmon pink) best seen on the anterior subendometrial layer just beyond the basalis The next layer is the thicker outer myometrium (maroon) that contains dilated vessels.

Post Menopausal uterus

Junctional Zone Prominent

In this 60 year old female with normal atrophied post menopausal uterus the transabdominal ultrasound in the sagittal plane reveals a normal view of the uterus with characteristic postmenopausal appearance. The stripe is thin measuring about 2mm homogeneously echogenic but also shows a hypoechoic halo of the junctional zone or inner myometrium. (salmon) The echogenic stripe is made up from a single histological layer the stratum basalis (deep yellow) The next layer as stated above is the compact myometrium – the junctional zone (aka inner myometrium) , and is followed by the thicker outer myometrium (maroon).

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The sagittal SPIR sequence from an MRI study shows a single large fibroid situated in the body of the uterus (green) and displacing and enlarging the remaining uterus forward and upward. The endometrial cavity is compressed (yellow) as is the junctional zone (salmon red) and the myometrium itself (maroon) The uterus has been lifted out of the pelvis and could be palpated clinically. The morphology of the swirling like shape to the myocardial tissue – an exemplary finding under the microscope is well appreciated in this image

MRI Thickened Junctional Zone

This T2 weighted MRI of a 41 year old female shows thickened junctional zone of the uterus measuring up to 12 mms characteristic of adenomyosis

Dystrophic Calcification in Subendometrial Region

52 year-old patient presents with menorrhagia. Two punctate echogenic nodule are in the subendometrial junctional zone, (overlaid in white in b) that are thought to represent dystrophic areas of calcification in prior foci of adenomyosis. The larger echogenic focus (green) was shown to be a benign hyperplastic polyp by pathology after a D and C. The polyp probably accounted for the patient’s menorrhagia. Note that the uterus is retroverted

Two Lesions in the Junctional Zone Impinging on the Endometrium

This patient presents with menorrhagia. Two echogenic nodules (overlaid in green) are seen in the subendometrial layer, (junctional zone). They are in close proximity and do appear to have appositional relationships with the endometrial stripe. They appear to and distort the endometrial lining. These findings could account for the patient’s menorrhagia. Note that the uterus is retroverted Included in the differential diagnosis are submucosal fibroids, and dystrophic changes in prior foci of adenomyosis. An MRI would be helpful in further characterizing these lesions in the subendometrial layer

References

Bioinfobank Library– Collection oif PAers on the Junctional Zone 5 star

Brosens JJ., Barker FG, and De Souza NM. Myometrial Zonal Differentaitionand uterine junctional zonehyperplasia in the non-pregnant uterus Human Reproduction Update 1998 Vol 4 No. 5 pp 496-502

McCarthy, S, Scott, Majumdar, S, Shapiro B, Thompson S, Lange R, Gore J Uterine junctional zone: MR study of water content and relaxation properties. Radiology. 1989 Apr ;171 (1):241-3

Willms AB Brown ED Keittritz UIRadiology 195 91-94 1995