NAVLE Reproductive

Equine Ovarian Abnormalities: Granulosa-Theca Cell Tumor – NAVLE Study Guide

Granulosa-theca cell tumors (GCTs) are the most common ovarian neoplasms in mares, representing approximately 2.5 to 5 percent of all equine tumors and more than 85 percent of ovarian tumors in horses. These

Overview and Clinical Importance

Granulosa-theca cell tumors (GCTs) are the most common ovarian neoplasms in mares, representing approximately 2.5 to 5 percent of all equine tumors and more than 85 percent of ovarian tumors in horses. These

sex cord-stromal tumors arise from granulosa cells alone or in combination with theca cells. While nearly always benign and unilateral, GCTs significantly impact mare behavior, reproductive performance, and athletic ability through abnormal hormone production. Understanding the pathophysiology, clinical presentation, diagnostic approach, and surgical management of GCTs is essential for NAVLE candidates, as these tumors present with highly testable clinical scenarios involving hormonal disturbances and behavioral changes.

Hormone Diagnostic Sensitivity Diagnostic Levels and Clinical Notes
Anti-Müllerian Hormone (AMH) 98% Normal: Less than 1 ng per mL GCT: Greater than 10 ng per mL, often greater than 60 ng per mL Gold Standard Test: Most sensitive and specific biomarker
Inhibin 80-90% Elevated in 80 to 90 percent of GCT cases Responsible for contralateral ovary suppression via FSH inhibition
Testosterone 48-50% Diagnostic: Greater than 100 pg per mL Associated with stallion-like behavior and masculinization
Combined Inhibin and Testosterone 84% Improves diagnostic accuracy when both hormones are measured together Use when AMH testing is unavailable

Etiology and Pathophysiology

Tumor Origin and Classification

Sex cord-stromal tumors of the ovary develop from granulosa cells, which are normally responsible for supporting oocyte development and producing estrogen. When theca cells are also present, the tumor is specifically termed a

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