The presence of endometrial cells on a cervical screening test, commonly known as a Pap smear, is an unexpected finding that prompts further inquiry. Although the Pap test screens for changes in cervical cells, it can inadvertently collect cells exfoliated from the uterine lining. The clinical importance of this result depends almost entirely on the patient’s age and menopausal status. Understanding the source of these cells and the context of the patient’s cycle determines whether this finding is a normal physiological occurrence or a signal for a potential underlying health condition.
Understanding Endometrial Tissue
The endometrium is the specialized tissue lining the inside of the uterus. This tissue is highly responsive to fluctuating reproductive hormones, specifically estrogen and progesterone. During the typical menstrual cycle, the endometrium thickens in preparation for a potential pregnancy. If conception does not occur, the outer layer of this thickened lining is shed during menstruation. This natural shedding process causes endometrial cells to detach from the uterine wall and travel through the cervix into the vaginal canal. These benign-appearing cells may be incidentally collected during a Pap smear and noted in the laboratory report.
Determining Clinical Significance
The primary factor dictating the significance of benign-appearing endometrial cells is the patient’s menopausal status and age. For pre-menopausal women who are still experiencing regular menstrual cycles, the presence of these cells is often considered normal, especially if the test was performed around the time of their period. This finding simply reflects the natural process of the uterine lining shedding.
The finding becomes more noteworthy, however, when cells are present “out of phase,” meaning the Pap smear was collected at a time when shedding is not expected. Current guidelines, such as The Bethesda System (TBS), often use an age cutoff of 45 years or older to help standardize reporting and identify patients who may need further evaluation.
The highest level of concern is reserved for post-menopausal women, for whom the presence of any endometrial cells is considered an abnormal finding requiring investigation. After menopause, the endometrium is thin and inactive due to low hormone levels, meaning natural exfoliation should not occur. The presence of these cells in post-menopausal women, even if they appear benign, suggests an underlying pathology within the uterus that is causing the cells to shed.
Conditions Indicated by Abnormal Presence
When endometrial cells are detected in an unexpected setting, such as in a post-menopausal patient or when the cells appear atypical, it signals the need to investigate the inner lining of the uterus. The most common underlying issues relate to conditions that cause abnormal growth or thickening of the endometrium.
Endometrial Hyperplasia
Endometrial hyperplasia is characterized by the overgrowth of the uterine lining, often driven by unopposed estrogen stimulation. Hyperplasia is classified into different types, ranging from simple non-atypical to complex atypical forms. The latter forms carry a significantly higher risk of progressing to cancer.
Endometrial Polyps
Another potential finding is the presence of endometrial polyps, which are localized growths of the endometrial tissue that can cause irregular bleeding or shedding. While generally benign, polyps can sometimes contain areas of hyperplasia or malignancy.
Endometrial Carcinoma
The most serious, though less frequent, condition indicated is endometrial carcinoma, or uterine cancer. The finding of benign endometrial cells on a Pap smear is not a diagnostic test for cancer itself, but it functions as a flag that prompts a focused evaluation of the uterine cavity. This evaluation is especially important for women over 50 years old, as they have a significantly higher rate of associated pre-neoplastic or neoplastic changes compared to younger women.
Subsequent Diagnostic Procedures
Following an abnormal Pap smear result involving endometrial cells, a physician initiates a series of focused diagnostic procedures to determine the cause of the shedding.
Transvaginal Ultrasound
The first step often involves a transvaginal ultrasound, which uses sound waves to create images of the uterus and measure the thickness of the endometrial lining. For a post-menopausal woman experiencing bleeding, an endometrial thickness of 5 millimeters or greater is often considered a threshold that mandates further tissue sampling.
Endometrial Biopsy
If the ultrasound shows a thickened lining or if the patient is post-menopausal, the next step is usually an endometrial biopsy. This is a quick, in-office procedure where a thin, flexible tube, often called a Pipelle, is inserted through the cervix into the uterus. The device then suctions a small tissue sample from the endometrium, which is sent to a pathology lab for definitive analysis to look for hyperplasia or malignancy.
Hysteroscopy and D&C
If the office biopsy is unsuccessful, inconclusive, or if there is a strong suspicion of a focal lesion that the blind biopsy might have missed, a hysteroscopy may be performed. Hysteroscopy involves inserting a thin scope with a camera through the cervix to allow the physician to visually inspect the entire uterine cavity. This procedure can be combined with a dilation and curettage (D&C) to obtain a more comprehensive tissue sample under direct visualization.