{
 "serie": "s4_SAG_PD_FS",
 "n_imgs": 16,
 "s": 55.0,
 "respuesta": "**Right ankle MRI – Sagittal PD FS (16 representative slices, medial → lateral)**\n\n**Joint fluid / synovium**\n- Tibiotalar joint effusion, mild–moderate, distending the anterior and especially the posterior recess (slices 8–12). Confidence: high.\n- Posterior subtalar (talocalcaneal) joint fluid and fluid tracking into the tarsal canal/sinus tarsi region (slices 9–12), with loss of the normal dark fat signal and hazy high signal around the interosseous talocalcaneal ligament – appearance suggests sinus tarsi synovitis/scarring (post-sprain \"sinus tarsi syndrome\"). Confidence: medium.\n- Prominent fluid in the posterior tibiotalar recess with a rounded intermediate/dark structure posterior to the talar body (slices 11–12) – possible os trigonum / posterior talar process with fluid at the synchondrosis (posterior ankle impingement pattern) vs. small intra-articular body. Confidence: low–medium.\n\n**Bones / cartilage**\n- Small focal high-signal subchondral lesion in the talar dome (slice 8, medial-central dome) – small subchondral cyst/osteochondral lesion. Confidence: medium.\n- Subchondral irregularity and adjacent high signal along the lateral talar dome/talar body at the tibiotalar articular surface (slices 11–12) – possible osteochondral lesion of the lateral dome with mild marrow edema. Confidence: medium.\n- Mild heterogeneous marrow signal in the talar body (slices 9–11) – mild reactive edema. Confidence: low.\n- Distal tibia, fibula, calcaneus, navicular, cuboid: no fracture line or significant marrow edema seen. Achilles insertion enthesis unremarkable.\n\n**Ligaments**\n- Anterolateral gutter (slices 12–13): amorphous intermediate/high signal soft tissue anterior to the distal fibula and lateral talus in the expected location of the anterior talofibular ligament, with joint fluid pooling in the gutter – findings consistent with chronic ATFL injury/thickening and anterolateral soft-tissue scarring (anterolateral impingement). Confidence: medium (sagittal plane limits ligament assessment; correlate with axial series).\n- Interosseous talocalcaneal / cervical ligament region obscured by fluid/edema as above. Confidence: medium.\n- Deltoid and spring ligament regions (slices 4–7): no gross abnormality identified on this plane. Low confidence given plane.\n\n**Tendons**\n- Posteromedial flexor compartment (slices 4–6): tubular high signal along the posterior tibial / FDL / FHL tendons – partly vessels, but some fluid within the tendon sheaths is likely (mild tenosynovitis, most probably FHL, which communicates with the joint). Confidence: low–medium.\n- Achilles tendon: normal thickness and signal (slices 9–12). Retrocalcaneal bursa: no significant fluid. Peroneal tendons (slices 12–13): no clear tear; perisheath assessment limited by peripheral fat-suppression failure.\n\n**Soft tissues**\n- No mass, no plantar fascia thickening at the calcaneal origin (slices 6–8). Kager fat pad clear.\n- Note: bright reticulated signal in the lateral/plantar subcutaneous tissues on the lateral slices (12–14) is due to incomplete fat suppression at the FOV periphery – artifact, not true edema.\n\n**Impression**\n1. Tibiotalar and posterior subtalar joint effusion with sinus tarsi/tarsal canal fluid and synovitis.\n2. Small osteochondral/subchondral lesion(s) of the talar dome (medial-central focus; possible lateral dome involvement) – recommend correlation with coronal images.\n3. Findings in the anterolateral gutter suggestive of chronic ATFL injury with anterolateral soft-tissue scarring (anterolateral impingement), consistent with the remote sprain history.\n4. Possible os trigonum/posterior impingement and mild medial flexor tenosynovitis – lower confidence, correlate with axial/coronal sequences."
}