A Comparison of the Volumetric Growth Rate of Nonfunctional Pituitary Microadenomas Versus Macroadenomas

Introduction: Many nonfunctional pituitary adenomas (NFPAs) are asymptomatic and discovered incidentally. Provider recommendation or patient choice often results in observation via serial MRIs. The frequency at which MRIs must be obtained during observation is unclear as the growth rate of these tumors is ill-defined. Uncertainty also exists as to whether the 1cm cutoff between microadenomas vs. macroadenomas is a true cutoff distinguishing low- vs. high-probability of future growth.

Methods: Eligible patients possessed a NFPA diagnosis between 1998 and 2022 and at least 2 surveillance MRIs at least 16 weeks apart. Adenomas were categorized as observed (decision to observe at initial visit, some of which went onto resection and some of which never got resected) versus surgical cases with serial MRIs (consented for surgery at diagnosis but happened to have multiple preoperative MRIs). Growth rate was calculated in mL per year based on volumetrics on serial MRIs.

Results: Our observed cohort included 44 microadenomas (15 of which went onto surgery) and 13 macroadenomas (10 of which went onto surgery). Our surgical cases with serial MRIs included 2 microadenomas and 11 macroadenomas. Mean (SD) time observed was 4.6 (3.9) years and this did not differ between microadenomas and macroadenomas (p = 0.36). Initial observed microadenoma volume was 0.18 ± 0.32 mL vs. 2.2 ± 1.6 mL in observed macroadenomas (p < 0.0001). Observed microadenomas were younger (mean [SD] years, 45.1 [13.8] vs. 65.3 [20.9]; p = 0.0001) and more female (77.3 vs. 38.5%; p = 0.02). The overall growth rate of observed microadenomas was lower than observed macroadenomas (mean [SD] mL/year, 0.02 [0.04] vs. 0.90 [1.39]; p < 0.001); and growth rate rose rapidly after 1 cm ([Fig. 1]). When excluding non-growing tumors, the growth rate of observed microadenomas remained lower (mean [SD] mL/year, 0.04 [0.05] vs. 1.06 [1.46]; p < 0.0001). Observed microadenomas were less likely to ultimately have surgery (34.1 vs. 76.9%; p < 0.0001; [Fig. 2]). Among observed adenomas that went onto surgery (15 microadenomas, 10 microadenomas), 80% (12 microadenomas, 8 macroadenomas) underwent surgery due to growth with the remaining due to patient preference changing from observation to surgery; and this did not differ by size (p = 1.0). Within their respective groups (microadenoma vs. macroadenoma), no significant growth rate differences existed between observed adenomas that did not go onto surgery, observed adenomas that went onto surgery, and surgical adenomas with serial MRIs (see [Table 1]). The percentage of stable adenomas did not differ between observed microadenomas and macroadenomas (40.9 vs. 15.4%; p = 0.11). Stable adenomas were younger than growing adenomas (mean [SD] years, 48.7 [17.1] vs. 63.7 [16.4]; p < 0.001; [Fig. 3]). When analyzed via multiple linear regression, initial diameter and age were not significant predictors of growth.

Conclusions: Most NFPAs grow when measured via volumetric analysis. Older patients are more likely to exhibit growth and may require more frequent MRI surveillance. While observed macroadenomas and microadenomas had comparable non-growth rates, 1 cm diameter was the inflection at which growth rate rose. Thus, macroadenomas can be observed but may require more frequent MRI surveillance and should be intervened upon as soon as their growth potential is identified.

Table 1

Fig. 1

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Artikel online veröffentlicht:
05. Februar 2024