At ultrasound examination the thyroid showed several nodules and micro- and macrocalcifications (a, b: white arrows, Case 1
). Microscopy showed in this case a HBF (heterotopic bone formation) focus in a thick rim of dense fibrosis (c, d: black arrow/HBF, asterisks/thyroid vesicles, and white arrow/intertrabecular fat with hematopoietic elements). Several HBFs were seen in Case 2
(e–k). A subcapsular nodule, largely fibrotic and atrophic, contained an infracentimetric HBF (e-f: black arrow/HBF, white arrow/nodular atrophic vesicles, and asterisk/reactive thyroid follicles). Another subcapsular HBF showed triangular shape and was situated in contact with an atrophic goiter nodule (g: black arrow/HBF, asterisk/thyroid vesicles, atrophic for some). A 3rd HBF was situated in contact with sheet-patterned fibrosis which contained large malformative vessels (h: black arrow/HBF, asterisks/thyroid vesicles, and white arrows/vessels). For this HBF, vesicles were at proximity and contact of bone trabeculae (i: black arrows). A 4th HBF was situated at proximity of intrathyroid adipose cells englobed in fibrosis (j: black arrow/HBF, white arrow/adipose cells). A 5th HBF was situated in a triangular-shaped zone of fibrosis, focally undulated, with an atrophic follicular nodule at contact (k: black arrow/HBF, asterisk/atrophic nodule). In Case 3
(l) a vaguely nodular zone, containing the HBF and thyroid vesicles, was delimited by undulated connective tissue (black arrows/HBF, asterisk/thyroid vesicles, and white arrows/undulated fibrosis with large vessels at contact). In Case 4
(m-n), the thyroid contained sheet-like fibrosis with large, malformative vessels at proximity and with ossification foci (m, n: black arrows/ossifications, white arrows/abnormal vessels). In Case 5
(o-p) the HBF was located in the subcapsular thyroid, at proximity to large malformative vessels (intra- and perithyroid) (o: black arrow/HBF, white arrow/malformative vessels, and asterisks/thyroid vesicles). The follicular nodule, situated at distance from the HBF, contained intervesicular disperse calcifications, some in the perivascular hyaline (p: black arrows).