{
 "serie": "s201_STIR_SAG",
 "n_imgs": 18,
 "s": 50.1,
 "respuesta": "**Series:** Sagittal STIR, right ankle/hindfoot; 18 slices progressing from lateral (forefoot/5th ray) to medial (medial malleolus/medial soft tissues). Image quality degraded on the far medial slices (noise, incomplete fat suppression at the periphery), which limits evaluation there.\n\n**Findings**\n\n1. **Tibiotalar joint effusion** – Increased fluid signal in the anterior and posterior recesses of the ankle joint (images 8–12), most conspicuous posteriorly on image 10 where fluid extends into the posterior tibiotalar recess. Small–moderate. Confidence: high.\n\n2. **Posterior subtalar joint fluid / synovitis** – Bright fluid signal in the posterior subtalar joint recess between talus and calcaneus (images 9–11), more than expected for a physiologic amount. Confidence: medium.\n\n3. **Sinus tarsi abnormality** – Fluid/edema-like high STIR signal replacing the normal (suppressed) fat within the sinus tarsi / tarsal canal, between the talar neck and anterior calcaneus (images 9–11; rounded bright collection on image 11). Suggests sinus tarsi syndrome (post-traumatic interosseous/cervical ligament injury with synovitis or small ganglion). Confidence: medium.\n\n4. **Talar dome – focal subchondral signal** – Small punctate/ovoid focus of high STIR signal within the central talar dome, subjacent to the tibiotalar articular surface (image 8, also faintly on image 9). Suspicious for a small osteochondral lesion / subchondral cyst or focal marrow edema. No definite displaced fragment. Correlate with coronal PD/T1. Confidence: medium.\n\n5. **Talar neck/head bone marrow edema** – Ill-defined high signal in the inferior talar neck adjacent to the sinus tarsi on images 10–11; may represent reactive marrow edema (or partly be the sinus tarsi fluid itself). Confidence: low.\n\n6. **Medial ankle soft tissues / flexor tendon compartment** – On the medial slices (images 13–15) there is increased signal surrounding the medial malleolus and linear/tubular high signal along the posteromedial tendons (posterior tibial / flexor digitorum longus region) consistent with tendon sheath fluid – mild tenosynovitis. Patchy high signal within the medial malleolus on image 14 could represent mild marrow edema, but this is at the noisy edge of the field of view. Confidence: low (limited by image quality).\n\n7. **Deltoid ligament region** – Heterogeneous increased signal deep to the medial malleolus (images 12–14) may reflect chronic deltoid ligament thickening/scarring after remote sprain; cannot be characterized reliably on sagittal images. Confidence: low.\n\n**Structures appearing normal (within the limits of this sequence)**\n- Achilles tendon: uniform low signal, normal thickness; no retrocalcaneal or pre-Achilles bursitis (images 9–12).\n- Calcaneus, navicular, cuboid, cuneiforms, metatarsals: no marrow edema or fracture line.\n- Plantar fascia: normal thickness at the calcaneal origin; no perifascial edema. Bright bands in the plantar forefoot (images 4–7) are most consistent with vessels/normal muscle rather than pathology.\n- Distal tibia: no marrow edema. Peroneal tendons (lateral slices) appear intact, no tendon sheath fluid.\n- No significant subcutaneous edema; no plantar or dorsal soft tissue mass.\n\n**Impression**\nPost-traumatic ankle with tibiotalar and posterior subtalar effusion, fluid/edema in the sinus tarsi (sinus tarsi syndrome), and a small focal subchondral lesion of the central talar dome (possible osteochondral lesion). Possible mild medial flexor tenosynovitis and chronic deltoid scarring – evaluate on axial/coronal sequences. Lateral ligament complex (ATFL/CFL) not assessable on this sagittal series."
}