Figure 1. Normal, Gestation Day 18. B6C3F1 mouse. The structure of the adrenal gland a gestation day 18 clearly shows the zona glomerulosa, zona fasciculata, and the medulla. Zona glomerulosa cells are arranged in small nests or packets and Zona fasciculata cells have begun to align in columns perpendicular to the capsular surface. Some intermingling of zona fasciculata and medulla cells can be seen as the corticomedullary junction is not sharply delineated.

Figure 2 (A81956) Normal cortex: Control B6C3F1 male in a 90-day study. The male adrenal cortex consists of the zona glomerulosa and zona fasiculata. The zona glomerulosa is a narrow poorly delimited band of nest of cells with round nuclei and scant cytoplasm located immediately below the capsule. The junction with the zona fasiculata is often difficult to clearly define as in this case. The zona fasiculata cells are polygonal to round with a centrally located nucleus and are arranged in single cell columns perpendicular to the capsular surface with fine capillaries between adjacent columns. The columnar arrangement is less obvious near the corticomedullary junction. Varying degrees of cytoplasmic vacuolation reflecting steroid synthesis and storage are present in the zona fasiculata. In this control male mouse from a 90-day toxicity study, the degree of cortical cytoplasmic vacuolation is within normal limits and would not typically be diagnosed and graded in a conventional toxicology study. Some degree of zona fasciculata cytoplasmic vacuolation is expected as a reflection of the circadian metabolic status of steroidogenesis.

Figure 3 (A81845). Normal adrenal: Control B6C3F1 male in a chronic study. In comparison to Figure 2 (A81956), the zona glomerulosa is more readily apparent and comprised of nests of cells with pale staining cytoplasm beneath the capsule. In this adrenal the columns of the zona fasiculata are less distinct in comparison with Figure 2 (A81956). A rich capillary network is present in the cortex and medulla. Also, the degree of cortical cell vacuolation is greater than in Figure 2 (A81956) and involves both zona glomerulosa and zona fasciculata.

Figure 4 (A81846). Normal adrenal: Control B6C3F1 male in a chronic study.
This is the contralateral adrenal in the same mouse as Figure 3 (A81845) and shows the extensive vascular system in the medulla. The subtle subcapsular cellular proliferation evident by closely packed basophilic nuclei is a normal occurrence in older mice. This degree of subcapsular hyperplasia is minimal and is an expected background change. It would typically not be diagnosed in evaluating a study unless there was a need to establish a grade for comparison to a potential treatment related response in mice exposed to a test agent or procedure. A small cluster of cells in the zona fasciculata consists of cells that are larger and more vacuolated than the surrounding zona fasciculata. These cells presumably have stored more cortical hormone but the reason for such a focal change is uncertain.

Figures 5a and 5b (A81973 & A81974). Normal adrenal. Adrenal from a normal male B6C3F1 mouse in a 90-day study. The cortex and medulla are normal and the low magnification of the adrenal (Figure 5a) shows a subtle variation in staining within the zona fasciculata. The paler staining areas of the zona fasciculata have slightly enlarged cells with finely vacuolated cytoplasm consistent with storage of cortical hormone. Present in the low magnification and more clearly in the higher magnification (Figure 5b) is the absence of an x-zone characteristic of the male mouse adrenal at this age. The normal medulla is characterized by small nests and packets of medullary cells.

Figures 6a and 6b (A81899 & A81900). Normal X-zone. Untreated female B6C3F1 mouse in a 90-day study. At the end of a 90-day study female B6C3F1 mice would be approximately 18 weeks old with a prominent adrenal x-zone as shown in right and left adrenal glands in this mouse. A small number of vacuolated cells are present within this x-zone but their presence or absence may vary among control female mice. Since this x-zone is within normal limits for this age mouse, a specific diagnosis is not necessary but its extent and appearance should be considered when evaluating possible accelerated x-zone involution in treated study cohorts. It is noted that the volume of the x-zone may vary depending a cross-section (Figure 6a) versus a more longitudinal section (Figure 6b).

Figure 7a and Figure 7b (A81923 & A81924). Normal x-zone: Control female B6C3F1 mouse in a 90-day study. The x-zone contains a mild scattering of vacuolated cells consistent with fatty change. X-zone fatty change in normal female B6C3F1 mice approximately 18 weeks of age is highly variable. This amount of x-zone fatty change is slightly greater than in Figures 6a and 6b. The degree of vacuolation of zona fasciculata cells is within normal physiological limits.

Figures 8a & 8b (A81920 & A81921). Normal x-zone with cytoplasmic vacuolation: Untreated female B6C3F1 mouse in a 90-day study. Prominent cytoplasmic vacuolation is present in this x-zone representing a more extreme example of vacuolar change sometimes present in adrenal glands in untreated 18-week old female mice (see Figures 6a, 6b, 7a, and 7b for comparison). Since this degree of cytoplasmic vacuolation is part of the variable spectrum of x-zone changes in 18-week old female mice, it need not be diagnosed but because of its extent it could be described in the study pathology narrative. While some pathologists have considered a diagnosis of fatty degeneration for this feature of the x-zone in a control of this age, this feature of the x-zone is a normal part of natural x-zone involution. It should be kept in mind that x-zone vacuolation (fatty change) is a non-exclusive form of normal x-zone involution. Involution can occur without any evi