Post-Traumatic / Postsurgical Breast Change

00Overview

乳房外傷與術後變化是乳房影像中最容易與惡性病變混淆的良性情境。影像任務核心是：(1) 辨識 fat necrosis、scar、seroma、hematoma 等 post-traumatic / postsurgical change 的完整影像光譜；(2) 區分這些良性變化與 recurrent / residual malignancy；(3) 判斷何時需要 biopsy 而非 follow-up。最容易出錯的地方：fat necrosis 在某些階段（early inflammatory phase 或 late spiculated scar）的影像表現可完全模擬 breast cancer。

01Critical concepts

• Fat necrosis 的影像表現取決於病程階段：acute（edema + hemorrhage）→ subacute（oil cyst formation）→ chronic（calcification + fibrosis / scar），每個階段的 imaging mimicry 不同
• Oil cyst 是 fat necrosis 的 pathognomonic finding：mammography 上見 lucent center + thin rim calcification（eggshell calcification）→ BI-RADS 2（benign）
• 術後乳房評估必須有 prior imaging 與 surgical history：lumpectomy / mastectomy / reconstruction type 直接影響 expected imaging appearance
• 術後 scar 在最初 6-12 個月內可能 progressively enhance on MRI，不應直接判為 recurrence → 需 baseline post-treatment MRI 在手術後 12-18 個月建立
• Post-lumpectomy scar 在 mammography 上應隨時間 stable 或 decreasing；若 serial follow-up 顯示 increasing in size 或 increasing density → 視為 suspicious，需 work-up
• Implant rupture 有 modality-specific signs：mammography 的 extracapsular silicone、US 的 stepladder / snowstorm sign、MRI 的 linguine sign / subcapsular line / keyhole-teardrop sign — 每一個都是高頻考點
• BI-RADS 4 必須 subdivide 為 4A / 4B / 4C：對應 low / moderate / high suspicion，與 PPV 與 management urgency 直接連動

01正常 anatomy / 常用 modality

術後乳房的正常解剖取決於手術類型：lumpectomy 後有 surgical cavity（可含 seroma / hematoma）+ architectural distortion；mastectomy 後有 skin flap + pectoralis muscle + possible reconstruction（implant 或 autologous flap）。

常用 modality：

• Mammography：首選 screening 與 diagnostic tool；術後 scar 在前 2-3 年的 mammographic follow-up 中逐漸穩定、縮小
• Ultrasound：評估 palpable concern、fluid collection（seroma / hematoma / abscess）、targeted biopsy guidance；亦為 implant rupture 的 first-line 評估（stepladder / snowstorm sign）
• Breast MRI with contrast：最敏感的 recurrence detection tool；同時為 silicone implant integrity 評估的 gold standard（silicone-sensitive sequence）；但 post-surgical enhancement 在早期可導致 false positive
• PET/CT：偶用於 suspected recurrence with equivocal MRI findings 或 staging

02常見 pattern 分類

Oil cyst / lipid cyst pattern

• Definition：mammography 上呈圓形或橢圓形的 radiolucent lesion，可有 thin rim calcification（eggshell / rim calcification）；US 可見 anechoic cyst with echogenic rim 或 complex cystic lesion
• Why it matters：是 fat necrosis 最具 pathognomonic 意義的表現，BI-RADS 2 即可；不需 biopsy，不需 follow-up
• What it points toward：prior trauma、prior surgery、prior radiation therapy、prior injection（如 silicone / filler）
• Common trap：若 oil cyst wall 較厚或有 focal nodular thickening → 需考慮 BI-RADS 4 with biopsy（rare malignancy can occur at fat necrosis site）

Spiculated mass / architectural distortion pattern

• Definition：mammography 上見 radial scar-like spiculation 或 focal architectural distortion，可有 central radiolucency 或 solid-appearing core
• Why it matters：fat necrosis 的 late fibrotic phase 可產生與 invasive carcinoma 幾乎 identical 的 spiculated mass → 是最具 mimic 挑戰的情境
• What it points toward：post-surgical scar（應隨時間 stable 或 decreasing）；fat necrosis with fibrosis；radial scar；invasive carcinoma
• Common trap：post-lumpectomy scar 在最初的 immediate postop mammogram 可能因 edema / hematoma 顯得較大，但建立 6-month baseline 之後，scar 應 stable 或 progressively decreasing in size；若 serial mammogram 顯示 increasing 或 increasing density → 視為 suspicious，需 diagnostic work-up 並考慮 biopsy

Fluid collection pattern

• Definition：well-defined fluid-density collection at surgical site，US 呈 anechoic or hypoechoic，可有 internal debris（hemorrhage）或 septations
• Why it matters：seroma 是 post-lumpectomy / post-mastectomy 最常見的 early finding，通常 self-resolving；需與 abscess 區分
• What it points toward：seroma（most common，sterile reactive fluid）；hematoma（early postop with hemorrhagic content）；abscess（thick wall + surrounding inflammation + clinical infection signs）
• Common trap：chronic seroma > 6 months 若出現 enhancing nodularity within the cavity wall on MRI → 需 biopsy to rule out recurrence

Post-radiation change pattern

• Definition：diffuse skin thickening + trabecular thickening + increased density of irradiated breast on mammography；MRI 見 diffuse parenchymal enhancement
• Why it matters：radiation 後的正常變化可持續數年，模擬 inflammatory breast cancer 或 diffuse disease
• What it points toward：normal post-radiation changes（expected after breast-conserving therapy）；若 asymmetric、focal、或 progressively worsening → evaluate for recurrence
• Common trap：post-radiation skin thickening 在對側乳房不應出現 — contralateral skin thickening 需考慮其他原因（lymphatic obstruction、heart failure、inflammatory carcinoma） Breast edema 時序軸：
• Acute / early phase (0-6 個月)：skin thickening 最厚（可達 5-10 mm）、trabecular thickening、diffuse increased density、breast volume increase due to edema
• Subacute (6 個月 – 2 年)：edema 逐漸消退，skin thickening 與 density 逐步減輕，是 baseline 評估的關鍵窗口
• Late / chronic (> 2 年)：殘餘 skin thickening 與 architectural distortion，應 stable；若 late onset 或 progressively worsening edema → 須排除 recurrent disease、lymphatic obstruction、radiation-induced angiosarcoma
• Lymphedema 評估：axillary dissection ± radiation 後，臨床觀察 arm circumference；影像上 US 可見 subcutaneous reticular pattern，MRI 可見 subcutaneous T2 hyperintensity；若單側 breast lymphedema 持續惡化 → 需排除 axillary recurrence 阻塞 lymphatic drainage

03Top common diagnoses

• Fat necrosis：最常見的 post-traumatic / post-surgical mimic，appearance 隨時間演變，oil cyst 為最 specific sign
• Post-lumpectomy seroma：幾乎所有 lumpectomy 後都有，大部分 6 個月內吸收，少數 persistent seroma 需追蹤
• Post-surgical scar / architectural distortion：mammography 上 stable 的 distortion 位於已知手術部位 → BI-RADS 2-3
• Post-reduction mammoplasty changes：large-volume tissue removal + redistribution → 影像上見 altered parenchymal pattern，scar lines，repositioned nipple；典型的 "swirled" parenchymal pattern 與 inferior pole 的 oil cyst / dystrophic calcification 群
• Breast implant complication：intracapsular / extracapsular rupture、capsular contracture、implant malposition — MRI 為 gold standard 評估
• PASH (Pseudoangiomatous Stromal Hyperplasia)：post-treatment 或 hormonally active 乳房中可見的 benign stromal proliferation，mammography / US 上呈 well-circumscribed oval mass，類似 fibroadenoma；常為 incidental biopsy diagnosis，需與 low-grade angiosarcoma 鑑別
• Desmoid tumor (fibromatosis)：少見但重要的 post-surgical mimic，特別是 implant capsule / chest wall 附近；MRI 上呈 T2 hypointense bands + 持續性 enhancement，infiltrative margin 易誤判為 recurrence

04Cannot-miss diagnosis / emergency

05高頻 mimics 與 discriminators

Fat necrosis vs invasive carcinoma

• Why they get confused：late-stage fat necrosis 的 spiculated mass 在 mammography 上幾乎與 invasive carcinoma 相同
• Most useful discriminators：(1) History — 已知 trauma / surgery site → fat necrosis more likely；(2) central lucency (fat density) on mammography → fat necrosis；(3) oil cyst 成分 on US → fat necrosis；(4) MRI — fat necrosis 常有 central fat signal (T1 bright，fat-saturated sequence 上 drop out)，carcinoma 不會；(5) stability on serial imaging → fat necrosis；(6) if uncertain → biopsy（BI-RADS 4）
• Common trap：早期 fat necrosis（inflammatory phase）可在 MRI 上呈現 intense enhancement + restricted diffusion，完全模擬 carcinoma → 此階段 biopsy 最 justified

Post-surgical scar vs recurrence on MRI

• Why they get confused：兩者都在 lumpectomy cavity 附近，都可有 enhancement
• Most useful discriminators：(1) 時間 — scar enhancement 在術後 6-18 個月內最強，之後逐漸減弱；recurrence 通常在 18 個月後出現且 progressive；(2) Enhancement pattern — scar typically 呈 thin linear enhancement；recurrence 呈 mass-like / irregular thick enhancement；(3) DWI — recurrence 常有 restricted diffusion，scar 無；(4) kinetic curve — scar 通常 persistent enhancement (Type I)；recurrence 常 washout (Type III)
• Common trap：radiotherapy-induced scar enhancement 可持續很久，因此 baseline post-treatment MRI（12-18 個月）是 indispensable reference

Seroma vs cystic recurrence

• Why they get confused：persistent post-lumpectomy seroma 可被 recurrence 取代（rare but documented）
• Most useful discriminators：(1) simple seroma 為 thin-walled, no enhancing nodularity；(2) cystic recurrence 有 enhancing mural nodule or irregular wall thickening；(3) new solid component developing within a previously simple seroma → biopsy；(4) FDG uptake in wall or nodule → suspicious
• Common trap：aspiration cytology 的 sensitivity 有限；若 MRI 有 enhancing mural nodule，即使 aspiration 為 benign cells，仍建議 tissue biopsy

Implant rupture — modality-specific signs

• Intracapsular rupture (silicone confined within fibrous capsule)：
  • Linguine sign (MRI, pathognomonic)：collapsed implant shell 漂浮在 silicone 內，呈 multiple curvilinear low-signal lines — 是 intracapsular rupture 的 hallmark
  • Subcapsular line / inverted teardrop sign：silicone 滲入 shell 內側 invagination，在 MRI 上呈 small focal collections 緊鄰 shell
  • Keyhole / teardrop / noose sign：shell 局部 invagination 形成 keyhole-shaped silicone collection — early intracapsular rupture
  • Stepladder sign (US)：multiple parallel echogenic horizontal lines within the implant，相當於 US 上的 linguine sign equivalent
• Extracapsular rupture (silicone outside fibrous capsule)：
  • Snowstorm / echogenic noise sign (US)：dirty echogenic shadowing in surrounding tissue 或 axillary node — silicone granuloma 的特徵
  • Mammography：extracapsular silicone globules outside implant contour
  • MRI：silicone signal outside fibrous capsule on silicone-sensitive sequence
• Saline implant rupture：collapse of implant，shell 塌陷在 chest wall 上，與 silicone rupture 評估方式不同
• Common trap：radial folds (normal invaginations of implant shell) 不應誤判為 keyhole sign — radial folds 不會包含 silicone outside the shell；keyhole sign 必定有 silicone tracking into the invagination

06Next step / protocol / appropriateness

影像 protocol 選擇：

• Post-lumpectomy routine follow-up：放射治療完成後 6-12 個月做 post-treatment baseline mammogram，之後 annual mammography → monitor surgical site for change
• Palpable concern at surgical site：diagnostic mammography + targeted US → assess for seroma, scar, recurrence
• Baseline post-treatment MRI：12-18 個月 post-therapy → establish enhancement baseline for future comparison
• Suspected recurrence：breast MRI with contrast → kinetics, morphology, DWI → BI-RADS assessment → biopsy if indicated
• Implant evaluation：MRI with silicone-sensitive sequences（water suppression + silicone-only protocol）；FDA 建議 silicone implant 患者 first MRI / US screening 在置入後 5-6 年，之後每 2-3 年

07Pitfalls / normal variants

• Post-operative architectural distortion 長期存在：lumpectomy scar 可在 mammography 上 persist indefinitely，只要 stable → benign；但若 increasing → concerning
• Nipple retraction after surgery ≠ recurrence：scar-related nipple retraction 需與 subareolar recurrence 鑑別 → 需 comparison with immediate post-op imaging
• Dystrophic calcification at surgical site：coarse, irregular calcifications at lumpectomy site are expected（fat necrosis dystrophic type），不同於 suspicious microcalcifications（fine linear branching）
• Autologous flap reconstruction 的 fat necrosis：TRAM / DIEP flap 的 fat necrosis 率高（10-20%），在 reconstructed breast 上看到 oil cyst / calcification is expected
• Silicone granuloma in lymph nodes：implant rupture 後 silicone 可 migrate 至 axillary lymph nodes，在 mammography 上呈 dense nodes（"snowstorm" on US），不應誤判為 metastatic adenopathy
• Radial folds vs intracapsular rupture：radial folds 為 normal implant shell invagination，shell 完整、不含 silicone tracking；linguine sign 則為 shell completely collapsed within silicone
• PASH mimicking fibroadenoma：post-treatment / hormonally active 乳房中可見 oval circumscribed mass，BI-RADS 通常 3-4A，需 biopsy 才能確診