Postprocedure / Postpartum Uterine Cavity Complication

00Overview

術後或產後 uterine cavity complication 是婦科與產科急診影像中的高頻情境。影像任務核心是：(1) 區分 retained products of conception (RPOC)、endometritis、blood clot、normal postpartum uterus；(2) 評估是否有 arteriovenous malformation (AVM) 或 ectopic pregnancy（含 cesarean scar ectopic）在介入前或介入後造成異常出血；(3) 偵測 uterine perforation 或 other procedural complication；(4) 在懷疑 placenta accreta spectrum (PAS) 時提供 MRI 補充評估。最容易出錯的地方：把正常 postpartum 的 endometrial debris / blood 誤判為 RPOC，導致不必要的 D&C；或在 EMV 未辨識下進行 D&C 造成 catastrophic hemorrhage。

01Critical concepts

• 正常 postpartum uterus 在產後數週內可見 endometrial cavity debris（blood + decidual tissue），這是 normal involutional process，不等於 RPOC
• RPOC 的超音波診斷關鍵是 vascularity：有 Doppler flow 的 endometrial mass > pure echogenic material without flow（blood clot no flow；RPOC has flow）
• Doppler vascularity 應量化：常用 Durfee / Kamaya color score 1–4（1 = 等同 normal myometrium，無 RPOC 內部 flow；2 = minimal flow；3 = moderate flow；4 = marked flow，幾乎等同 EMV）→ score ≥ 2 + clinical context 即提示 RPOC；score 4 多需 IR 介入而非 D&C。Peak systolic velocity (PSV) > 20 cm/s 提示明顯 vascular RPOC，> 60–80 cm/s 偏向 EMV/AVM
• Endometrial thickness 在 postpartum 不是好的 diagnostic criterion：正常 postpartum 子宮內膜可 thickened with heterogeneous content；文獻上常引用的 reporting threshold 為 endometrial / cavity AP thickness > 10 mm（部分研究採 ≥ 13 mm）合併 mass-like morphology 才較具特異性，single threshold 不可靠
• Enhanced myometrial vascularity (EMV) / uterine AVM 可在 RPOC、molar pregnancy、或 post-D&C 後出現，若在 D&C 前未辨識 → 可能 catastrophic hemorrhage
• Cesarean scar 相關病變要主動排除：包含 cesarean scar ectopic pregnancy (CSP) 與 isthmocele（niche）— 兩者解剖位置相同但臨床意義截然不同

01正常 anatomy / 常用 modality

正常 postpartum uterus 在產後立即開始 involution：子宮大小在 6-8 週後回到接近正常大小。產後 1-2 週的 endometrial cavity 可含 blood、decidual tissue、small echogenic debris，稱為 lochia。正常 placental site involution 可見 myometrial thinning 與 focal increased vascularity（subinvolution of placental site，多在 6–8 週內 resolve）。

常用 modality：

• Transvaginal ultrasound (TVUS) with Doppler：首選，可評估 endometrial cavity content、vascularity、myometrial integrity；color Doppler 應使用 low PRF setting 以避免低估 flow
• Transabdominal ultrasound (TAUS)：大範圍評估（uterine size、free fluid、adnexal pathology）
• CT with contrast：suspected perforation、sepsis、abscess、hemorrhage → 快速評估
• MRI pelvis：equivocal US cases、placenta accreta spectrum 的術前 mapping、myometrial invasion 評估、可疑 cesarean scar ectopic 之 anatomic clarification
  • PAS MRI signs：T2 dark intraplacental bands、abnormal placental bulge / myometrial bulge（子宮輪廓 focal outward convexity）、loss of T2 hypointense myometrial line、bladder tenting / bladder wall interruption、focal myometrial thinning（< 1 mm）、placental heterogeneity、abnormal vascularity at uteroplacental interface

02常見 pattern 分類

Echogenic endometrial mass with vascularity

• Definition：TVUS 見 endometrial cavity 內 echogenic mass（通常 > 10 mm thickness），Doppler 顯示 internal vascularity（arterial waveform with low resistance，PSV 常 > 20 cm/s）
• Why it matters：高度提示 RPOC，需要 intervention（surgical evacuation 為主）
• What it points toward：RPOC（retained placental tissue 或 fetal parts）；rare: endometrial neoplasm（gestational trophoblastic disease [GTD]）
• Quantification：使用 Color score 1–4 (Durfee / Kamaya)；score 2–3 → likely RPOC；score 4 → consider EMV / AVM 並避免 blind D&C
• Common trap：small amount of Doppler flow in a thin echogenic stripe 不等於 RPOC → 需要 threshold（mass-like morphology + definite internal flow + clinical bleeding）

Heterogeneous endometrial content without vascularity

• Definition：TVUS 見 endometrial cavity 內 heterogeneous echogenic material，無明確 Doppler signal（color score 1）
• Why it matters：最常見的 postpartum / post-procedure finding，通常代表 blood clot + decidual debris（normal involution）
• What it points toward：normal postpartum / post-D&C changes；organized hematoma；rarely early RPOC（flow may not be detectable yet）
• Common trap：没有 flow 不能 100% 排除 RPOC（avascular RPOC exists），但 probability 顯著降低 → 臨床 follow-up reasonable if no active bleeding

Enhanced myometrial vascularity (EMV) / uterine AVM pattern

• Definition：myometrium 內見 prominent vascular channels with turbulent flow（color Doppler 見 aliasing / mosaic pattern），peak systolic velocity 常顯著 elevated（> 60–80 cm/s，部分病例 > 100 cm/s），low resistance waveform
• Why it matters：若在計畫 D&C 前發現 → 改變 management（embolization 優先，避免 curettage 造成 massive hemorrhage）
• What it points toward：post-gestational EMV（most common — transient, 常在 RPOC 或 molar pregnancy 後）；true congenital uterine AVM（rare，pre-existing）；post-D&C traumatic AVM
• Common trap：post-gestational EMV 多數會 spontaneously resolve in weeks to months → 不需 intervention unless actively bleeding；只有 active hemorrhage + EMV 才需 emergent embolization

Gas within endometrial cavity pattern

• Definition：ultrasound 見 endometrial cavity 內 hyperechoic foci with dirty shadowing（gas）；CT 見 intrauterine air
• Why it matters：少量 gas 在 post-procedure 24-48 小時內可正常存在；但合併 clinical infection signs → endometritis / pyometra / septic abortion
• What it points toward：normal post-procedure finding（< 48 hours）；endometritis（fever + pain + leukocytosis + gas）；uterine perforation（gas + free fluid + extraluminal gas）
• Common trap：gas 在 C-section 後的子宮切口區域也可少量存在 → 需結合 clinical context

03Top common diagnoses

• Retained products of conception (RPOC)：postpartum 或 post-abortion 持續出血 + endometrial mass with vascularity（color score ≥ 2）；treatment 為 suction D&C；medical management 多採 misoprostol（methotrexate 主要用於 ectopic / GTD，非標準 RPOC 一線藥物）
• Endometritis：postpartum / post-procedure fever + pelvic pain + uterine tenderness；TVUS 見 thickened heterogeneous endometrium + possible gas + possible fluid；treatment 為 antibiotics
• Postpartum hemorrhage (PPH) with blood clot：endometrial cavity 內 large avascular echogenic mass（organized clot）→ 若 no active bleeding 可 conservative management
• Gestational trophoblastic disease (GTD)：
  • Complete hydatidiform mole：markedly elevated beta-hCG + enlarged heterogeneous endometrial / intracavitary mass with multiple small cystic spaces（modern TVUS 描述；舊文獻 transabdominal 稱 "snowstorm appearance"）；常合併 bilateral theca lutein cysts（high hCG-mediated）
  • Partial mole：placenta 內 focal cystic spaces + co-existing fetal parts / abnormal gestational sac；hCG 上升幅度較 complete mole 低
  • Invasive mole / choriocarcinoma：MRI 見 myometrial mass with marked hypervascularity、prominent flow voids、heterogeneous T2 signal、early avid enhancement，可侵犯 parametrium 或合併 lung metastases
• Cesarean scar ectopic pregnancy (CSP)：gestational sac implanted at lower anterior uterine segment within cesarean scar niche；TVUS 特徵 empty uterine cavity & empty endocervical canal、sac embedded in anterior myometrium with thin or absent overlying myometrium (often < 5 mm) towards bladder、prominent peritrophoblastic flow；屬 cannot-miss，D&C 可造成 uterine rupture / massive hemorrhage → 多需 medical (methotrexate) ± UAE ± hysteroscopic / surgical excision
• Uterine perforation：post-D&C complication → CT 見 myometrial defect + free fluid ± free air + possible omental / bowel herniation through defect

04Cannot-miss diagnosis / emergency

05高頻 mimics 與 discriminators

RPOC vs blood clot in endometrial cavity

• Why they get confused：兩者都是 echogenic endometrial content on TVUS
• Most useful discriminators：(1) Doppler — RPOC has internal vascularity（color score ≥ 2，low-resistance arterial flow，PSV often > 20 cm/s），blood clot has no flow（score 1）；(2) morphology — RPOC 常 mass-like with irregular borders；clot 常 amorphous and changes shape with manual compression；(3) beta-hCG — elevated or slowly declining → RPOC；rapidly declining → clot；(4) serial imaging — clot resolves on follow-up；RPOC persists or grows
• Common trap：small avascular RPOC exists but is uncommon → if clinical suspicion high + no flow → follow beta-hCG trend

Post-gestational EMV vs congenital uterine AVM

• Why they get confused：Doppler morphology 可非常相似（turbulent flow in myometrium）
• Most useful discriminators：(1) history — EMV occurs after pregnancy / D&C / molar pregnancy；congenital AVM has no gestational trigger；(2) natural history — EMV resolves spontaneously in weeks to months；congenital AVM does not；(3) EMV 常 associated with RPOC / elevated hCG；(4) congenital AVM 見 distinct nidus with feeding arteries + draining veins on MRI/angiography
• Common trap：初次發現時無法確定是 EMV 或 congenital AVM → 若 no active bleeding → follow-up in 4-6 weeks → resolution = EMV

Cesarean scar ectopic pregnancy vs isthmocele (niche) with blood

• Why they get confused：兩者皆位於前壁下段 C-section scar 區域，TVUS 可呈現 cystic content within scar
• Most useful discriminators：(1) beta-hCG — CSP positive and rising；isthmocele 為 anatomic defect，hCG negative（除非合併 menstrual blood retention）；(2) Doppler — CSP 見 peritrophoblastic ring of flow；isthmocele 內血液無 internal flow；(3) content — CSP 含 gestational sac ± yolk sac / embryo；isthmocele 為 fluid/blood-filled triangular defect；(4) uterine cavity — CSP 時 cavity & endocervical canal empty；isthmocele cavity 正常
• Common trap：早期 CSP 在 sac 尚小、yolk sac 未明時可被誤判為 isthmocele 或 incomplete miscarriage → beta-hCG + sac 位置（embedded in anterior myometrium，非 cavity 內或 cervical canal 內）是 key

Endometritis vs normal postpartum endometrium

• Why they get confused：postpartum endometrium 正常可 thickened + heterogeneous + contain small gas bubbles（< 48 hrs）
• Most useful discriminators：(1) clinical — endometritis 有 fever + uterine tenderness + foul-smelling lochia；(2) gas > 48 hours postpartum without recent procedure = suspicious；(3) endometrial fluid — purulent (echogenic) > simple serous；(4) myometrial heterogeneity + parametrial fat stranding → infection extending beyond endometrium
• Common trap：endometritis 是 primarily a clinical diagnosis — 影像 alone cannot confirm or rule out；report 應 describe findings and recommend clinical correlation

06Next step / protocol / appropriateness

影像 protocol 選擇：

• Postpartum / post-procedure bleeding：TVUS with Doppler → assess endometrial content + vascularity（記錄 color score 1–4 與 PSV）→ determines RPOC vs clot vs EMV
• Suspected RPOC with vascularity：grayscale + color Doppler + spectral Doppler of endometrial content → if vascular → plan evacuation vs medical management（misoprostol）
• Suspected EMV / AVM：TVUS Doppler → if PSV > 60–80 cm/s or color score 4 → CT angiography 或 MRI for vascular mapping → interventional radiology consultation for possible embolization
• Suspected cesarean scar ectopic：TVUS sagittal anterior lower segment → assess sac location, overlying myometrial thickness, peritrophoblastic flow → MRI 補充若 anatomy 不清 → 避免 transcervical instrumentation 前必先排除
• Suspected PAS（產前）：grayscale TVUS/TAUS + color Doppler → MRI 評估 T2 dark bands、myometrial bulge、bladder involvement → 多科團隊規劃
• Suspected perforation：CT abdomen/pelvis with IV contrast → myometrial defect, free fluid, pneumoperitoneum
• Follow-up protocol：if no active bleeding + avascular endometrial content → repeat US in 1-2 weeks + serial beta-hCG → resolution confirms clot/normal involution

07Pitfalls / normal variants

• Normal postpartum subinvolution of placental site：focal myometrial vascularity at placental implantation site 可在產後數週 persist → 不等於 AVM → follow-up resolves
• Post-cesarean section niche (isthmocele)：C-section scar defect 可 accumulate blood / fluid → mimics endometrial pathology on TVUS → sagittal view 可 confirm anterior lower segment location；務必與 cesarean scar ectopic 鑑別（後者 hCG positive + 有 gestational sac）
• IUD-related echogenic focus：IUD in endometrial cavity 可產生 shadowing + surrounding echogenic halo → 不應與 RPOC 混淆
• Endometrial polyp vs RPOC：非 postpartum 情境中 echogenic endometrial mass with feeder vessel → more likely polyp than RPOC → clinical context essential
• Normal decidualized endometrium in ectopic pregnancy：intrauterine decidual reaction without gestational sac（"pseudosac"）→ 不是 RPOC → 需 complete ectopic workup
• Endometrial thickness pitfall：postpartum cavity AP measurement 受 lochia / clot 影響極大，single cutoff 不可靠；> 10 mm 僅作為 reporting reference，必須結合 vascularity 與 clinical context