Papillary thyroid carcinoma (PTC) encompasses several histological variants with distinct clinicopathological features. The coexistence of multiple variants within the same thyroid gland, particularly across both lobes, is rare and may provide insights into tumor heterogeneity and progression pathways.

The clinical presentation, laboratory findings, and imaging results of a patient diagnosed with Concurrent occurrence of conventional PTC, infiltrative follicular variant of papillary thyroid carcinoma (FVPTC), and encapsulated FVPTC.

We report a 57-year-old woman presenting with a right thyroid mass. Ultrasound and CT revealed bilateral thyroid nodules, and fine-needle aspiration suggested malignancy. The patient underwent right thyroidectomy then complete thyroidectomy with central neck lymph node dissection. Histopathologic examination demonstrated three distinct PTC variants, including Conventional (classic) PTC in the right lobe; Infiltrative follicular variant of PTC (FVPTC) in the left lobe; Non-invasive encapsulated FVPTC also in the left lobe. The encapsulated lesion showed a well-defined capsule without invasion, while the infiltrative component exhibited stromal invasion and irregular follicular architecture. Postoperatively, the patient was started on levothyroxine replacement. I-131 whole-body scan revealed residual functioning thyroid tissue without evidence of distant metastasis. Discussion: This case illustrates the coexistence of three morphologically distinct PTC variants within one thyroid gland, underscoring the importance of precise histopathologic subclassification. The concurrent presence of non-invasive and infiltrative FVPTC supports a biologic continuum between non-invasive and invasive follicular-patterned lesions, reflecting differing degrees of malignant potential. Accurate recognition of NIFTP prevents unnecessary aggressive treatment, while identification of infiltrative FVPTC ensures appropriate risk stratification. The additional finding of conventional PTC highlights the multifocal and heterogeneous nature of thyroid carcinogenesis, potentially driven by independent molecular events. Recognition of such mixed variants is crucial for accurate diagnosis, risk stratification, and individualized management.

Concurrent occurrence of conventional PTC, infiltrative FVPTC, and encapsulated FVPTC in one patient is exceedingly rare and highlights the spectrum of differentiation and invasive potential within papillary thyroid carcinoma.