A Papanicolaou (Pap) smear is a routine screening procedure designed to detect changes in the cells of the cervix that could indicate a risk for cervical cancer. The test involves collecting a sample of cells from the cervix and the surrounding area for microscopic examination. When a Pap smear reports the presence of endometrial cells, it means cells originating from the lining of the uterus, known as the endometrium, were found in the sample. This finding is relatively uncommon on a cervical screening test, and its significance depends entirely on the patient’s age and menstrual status.
What Endometrial Cells Are and Why They Appear
Endometrial cells are the specialized epithelial cells that form the inner lining of the uterus. This tissue undergoes cyclical changes each month in response to fluctuating hormones, thickening to prepare for a potential pregnancy. If pregnancy does not occur, the top layer of the endometrium is shed during menstruation.
The mechanism by which these cells reach the Pap smear collection site is through this normal physiological shedding. During a menstrual period, the cells slough off from the uterine wall and travel down through the cervix and vagina. They can be inadvertently collected during the Pap smear procedure, especially if the test is performed when the patient is actively menstruating or shortly after the flow has stopped.
Age Matters: Normal Versus Abnormal Findings
The clinical significance of finding endometrial cells is determined by whether the patient is premenopausal or postmenopausal. For a premenopausal patient, the presence of benign-appearing endometrial cells is typically considered a normal physiological event, provided the Pap smear was performed during the correct phase of the menstrual cycle. Specifically, if the cells are collected within the first 12 days of the menstrual cycle, they are usually considered “in-cycle” and are shed as part of the normal process.
If a premenopausal patient has benign endometrial cells present more than 12 days after the start of their last menstrual period, the finding is considered “out-of-cycle” and warrants closer attention. Even in this scenario, the majority of follow-up evaluations are benign, but the out-of-cycle finding indicates a potential for abnormal shedding. The interpretation changes dramatically for a postmenopausal patient, who should no longer be experiencing the cyclical shedding of the endometrium.
The presence of any endometrial cells in a postmenopausal patient, even if they appear benign under the microscope, is considered an abnormal finding that requires investigation. The uterine lining in these patients should be atrophic and stable, meaning any shedding is unexpected. Studies have shown that a substantial percentage of postmenopausal women with this finding have underlying endometrial pathology. This unexpected cellular activity in a non-menstruating patient is the primary trigger for further diagnostic workup.
When the Finding Indicates Potential Risk
The presence of endometrial cells is a screening finding that serves as a flag for potential issues deeper within the uterus, such as endometrial hyperplasia or carcinoma. The pathologist’s report will categorize the cells, which helps determine the level of risk.
Cells labeled as “atypical” or “malignant” carry a higher probability of representing a serious underlying condition. Atypical endometrial cells show microscopic changes that are suggestive of precancerous conditions, such as atypical hyperplasia, or frank carcinoma. Endometrial hyperplasia is a condition where the uterine lining becomes excessively thick due to an overgrowth of cells, which can be a precursor to cancer.
Endometrial cancer affects the lining of the uterus, not the cervix, but the shedding of cancerous cells can lead to their collection on the Pap smear. In postmenopausal women, the finding of benign endometrial cells alone has been associated with a risk of significant pathology. Therefore, the Pap smear acts as an indirect indicator, alerting the clinician to investigate the uterine cavity, where the primary pathology resides.
Physician Follow-Up and Diagnostic Testing
When a Pap smear returns an abnormal finding, such as endometrial cells in a postmenopausal patient or atypical cells, the physician will recommend specific diagnostic steps. The primary goal is to examine the endometrium directly to rule out hyperplasia or cancer. The initial step typically involves transvaginal ultrasound, which uses sound waves to measure the thickness of the endometrial lining.
If the ultrasound reveals an abnormal endometrial thickness, or if the patient is postmenopausal with endometrial cells, the next procedure is usually an endometrial biopsy. This office-based procedure involves taking a sample of the uterine lining tissue. The tissue sample is then sent to a lab for histopathological analysis, which provides a definitive diagnosis.
If the initial endometrial sampling is insufficient or non-diagnostic, or if the ultrasound suggests a focal abnormality like a polyp, a hysteroscopy may be recommended. Hysteroscopy involves inserting a thin, lighted telescope through the cervix into the uterus, allowing the physician to visually inspect the entire uterine cavity. This procedure can be combined with a targeted biopsy to ensure the removal of any suspicious areas.