Australian Society of Cytology

Case of the Month

January 2005 - Answer and Discussion

Transitional Cell Metaplasia

Answer

This patient presented to the Mayne Health Laverty Pathology’s Cytology Department with one conventional slide and one ThinPrep Slide. Suspicious cells found by the primary screener, as seen in Figures 1-5, initially were thought to be ‘Inconclusive-Atypical Immature Metaplasia’. However, on review, these cells were classified as benign changes, namely Transitional Cell Metaplasia (TCM).

Discussion

So, what is TCM?

TCM is the benign metaplastic change of the cervix and vagina that resembles urothelium. It is usually seen in perimenopausal and postmenopausal women that are not on exogenous hormone replacement therapy (HRT). It is also associated with an atrophic cell pattern.

TCM of the cervix is frequently underdiagnosed and a poorly recognised entity1. It is most commonly found on Fallopian tube serosa (Walthard’s nests) and also on the ovary, broad ligament, vulva and male genital tract2. The pathogenesis of TCM is unknown, but is presumed to arise as a consequence of an altered hormonal environment (drop in circulating oestrogens, rise in androgens).

TCM is usually an incidental finding of patients with ovarian masses, postmenopausal bleeding (PMB) and Squamous Intraepithelial Lesions (SIL).

The cytological features of TCM, seen in Figure 1-5, are as follows:

Cohesive sheets of cells
(multilayered and/or streaming arrangement)
Low N:C ratio
Nuclear features
- 1.5 - 2.5 X size of intermediate nucleus
- oval to spindle shapes with tapered ends
- longitudinal nuclear grooves
- ‘powdery’ chromatin structure
- may have irregular nuclear contours
- small nucleoli
Perinuclear halos
Pale cytoplasm
Mitoses absent or rare

The differential diagnosis of TCM include High-Grade SIL (HSIL), atrophy-related changes and Tubal Metaplasia (TM). Table 1 highlights the cytological differences between them and TCM.

Table 1: Characteristics of TCM and its mimickers
(adapted from Weir and Bell (1997)3

In summary, to distinguish between TCM and its mimickers, look at the following:

1. CLINICAL DETAILS
TCM occurs in an older patient population than SIL.

2. NUCLEAR SHAPE
TCM has oval, spindled, tapered nuclei compared to round, oval as seen in other entities.

3. NUCLEAR GROOVES
Present in TCM, rare in atrophy & SIL.

4. PERINUCLEAR HALOS
Present in TCM, absent in other entities.

References:

1. Egan AJM, Russell P: Transitional (urothelial) cell metaplasia of the uterine cervix: morphological assessment of 31 cases. Int J Gynecol Pathol. 1997;16:89-98.

2. Weir MM, Bell DA, Young RH: Transitional cell metaplasia of the uterine cervix and vagina: an underrecognised lesion that may be confused with high-grade dysplasia. Am J Surg Pathol. 1997;21:510-517.

3. Weir MM, Bell DA: Transitional cell metaplasia of the cervix: a newly described entity in cervicovaginal smears. Diagn Cytopathol. 1998;18:230-235.