Splenic Emergency in the Nontraumatic Setting

00Overview

非外傷性脾臟急症涵蓋 splenic infarction、spontaneous rupture、abscess、sequestration crisis 等。影像任務核心是：(1) 辨識非外傷性脾臟急症的 CT pattern；(2) 區分 infarction、abscess、hemorrhage 的不同處置方向；(3) 評估 underlying etiology（hematologic malignancy、endocarditis、portal hypertension）。最容易出錯的地方：把 splenic infarction 的 left upper quadrant pain 誤判為 renal colic 或 pancreatitis，延遲病因探查。

01Critical concepts

• Splenic infarction 最常見的病因是 cardioembolic（atrial fibrillation、endocarditis、mural thrombus），其次是 hematologic disease（sickle cell、myeloproliferative neoplasm [MPN]）與 hypercoagulable states
• Spontaneous (atraumatic) splenic rupture 最常見於 pathologic spleen（splenomegaly from hematologic malignancy、EBV mononucleosis、malaria），正常大小的脾臟極少 spontaneous rupture
• Splenic abscess 罕見但 mortality 偏高；早年文獻在無治療下可達 ~50%，但在現代影像引導 percutaneous drainage + broad-spectrum antibiotics 時代，mortality 已明顯下降（約 10–20%），仍需早期辨識
• Splenic artery aneurysm (SAA) 是 visceral artery aneurysm 中最常見的（約 60–70%，實際比例依文獻略有差異），> 2 cm 有 rupture risk，pregnancy 期間 rupture mortality 極高（maternal mortality 可達 70%、fetal mortality > 90%）
• Sickle cell disease 在成人常呈 autosplenectomy：repeated infarction 導致 small, shrunken, densely calcified spleen — 為高頻考點

01正常 anatomy / 常用 modality

脾臟位於 left upper quadrant，正常大小約 12 cm longitudinal length（> 13 cm = splenomegaly）。Splenic artery 從 celiac trunk 起源，走行於 pancreas 上緣，常有 tortuous course。脾臟是 end-organ arterial supply — segmental infarction 產生 wedge-shaped pattern。

常用 modality：

• CT with IV contrast：首選急診評估 — infarction（wedge defect）、hemorrhage（hemoperitoneum + active extravasation）、abscess（rim-enhancing collection）
• Ultrasound：bed-side screening — free fluid、spleen size、focal lesion
• CT angiography：splenic artery aneurysm 評估、active bleeding source localization
• MRI：characterize splenic lesions（lymphoma vs metastasis vs benign）in non-emergent setting；SWI / GRE 對 siderotic nodules（Gamma-Gandy bodies）與 hemorrhagic products 敏感度高

02常見 pattern 分類

Wedge-shaped splenic perfusion defect

• Definition：contrast-enhanced CT 上 peripheral-based wedge-shaped area of non-enhancement，apex 指向 hilum
• Why it matters：classic splenic infarction pattern；需尋找 embolic source 或 hematologic cause
• What it points toward：cardioembolic（AF、endocarditis、LV thrombus）；hematologic（sickle cell、MPN、leukemia）；splenic artery thrombosis
• Common trap：heterogeneous early splenic enhancement（"zebra spleen" / tiger striping）is a normal variant on arterial phase → 不是 infarction；需在 portal venous phase 確認

Perisplenic / intraperitoneal hemorrhage without trauma

• Definition：high-density free fluid surrounding spleen + possible splenic parenchymal disruption + active extravasation，without trauma history
• Why it matters：nontraumatic splenic rupture 是 surgical / IR emergency；常見於 pathologic spleen
• What it points toward：EBV mononucleosis with splenic rupture（young patient）；hematologic malignancy with splenic involvement；anticoagulation-related hemorrhage；splenic artery aneurysm rupture
• Common trap：history of "no trauma" 需仔細 re-query — minor trauma（coughing, straining）in pathologic spleen 可 trigger rupture

Rim-enhancing splenic collection

• Definition：splenic parenchyma 內 or 周圍的 hypodense collection with peripheral rim enhancement + possible internal gas
• Why it matters：splenic abscess 需 drainage + antibiotics；internal gas is highly specific
• What it points toward：hematogenous seeding（endocarditis → septic emboli → abscess）；contiguous spread（perinephric abscess、diverticulitis with fistula）；infected infarct
• Common trap：infarcted spleen with liquefaction 可 mimic abscess on CT → clinical distinction（fever + leukocytosis → abscess）；peripheral rim enhancement alone is also seen in subacute infarct

Massive splenomegaly with complications

• Definition：spleen >> 20 cm with parenchymal heterogeneity + complications（subcapsular hematoma、infarction、compression of adjacent organs）
• Why it matters：massive splenomegaly 本身就增加 spontaneous rupture risk；underlying cause 決定 treatment
• What it points toward：hematologic malignancy（CML、hairy cell leukemia、myelofibrosis）；storage diseases（Gaucher）；lymphoma with splenic involvement；portal hypertension
• Common trap：splenic lymphoma 可呈 diffuse infiltration without focal mass → splenomegaly alone on imaging → tissue sampling or clinical context needed

03Top common diagnoses

• Splenic infarction：most common splenic emergency in nontraumatic setting；wedge-shaped hypodensity on CT
• Spontaneous splenic rupture：rare but life-threatening；most cases have pathologic spleen
• Splenic abscess：associated with endocarditis、immunosuppression、sickle cell disease
• Splenic artery aneurysm (SAA)：most common visceral artery aneurysm；often incidental；> 2 cm = intervention
• Splenic vein thrombosis：causes left-sided (sinistral) portal hypertension → isolated gastric varices without esophageal varices；associated with pancreatitis
  • CT 影像表現：splenic vein 內 hypodense filling defect + non-enhancement；secondary signs 包含 (1) gastric fundal / short gastric / gastroepiploic varices（patent left gastric / coronary vein 仍可呈 esophageal varices）；(2) perigastric & perisplenic collateral vessels；(3) splenomegaly；(4) 常合併 pancreatitis、pancreatic ca、pseudocyst 壓迫 splenic vein

04Cannot-miss diagnosis / emergency

05高頻 mimics 與 discriminators

Splenic infarction vs splenic lymphoma

• Why they get confused：both can present as hypoattenuating splenic lesion on CT
• Most useful discriminators：(1) infarction is peripheral wedge-shaped；lymphoma is round / mass-like；(2) infarction 急性期可有 slight enhancement（subacute phase）→ evolves to scar；lymphoma persists or grows；(3) clinical — infarction has acute LUQ pain + elevated LDH；lymphoma has B symptoms + LAD；(4) multiple wedge defects + cardiac source → infarction
• Common trap：lymphoma involvement can also cause infarction（tumor compression of splenic vessels）→ both can coexist

"Zebra spleen" (normal variant) vs splenic infarction

• Why they get confused：arterial phase CT 的 normal heterogeneous splenic enhancement 看起來像 multiple perfusion defects
• Most useful discriminators：(1) zebra spleen is ONLY on arterial phase → portal venous phase shows homogeneous enhancement；(2) infarction persists on all phases；(3) zebra spleen has no clinical symptoms；(4) zebra spleen is bilateral / diffuse；infarction is usually focal / wedge-shaped
• Common trap：radiologists unfamiliar with this variant may urgently call splenic infarction on early-phase CT → wait for portal venous phase

Splenic abscess vs cystic splenic lesion

• Why they get confused：both can appear as hypoattenuating lesion with peripheral enhancement
• Most useful discriminators：(1) abscess has clinical infection signs（fever, leukocytosis）；cyst does not；(2) abscess may have internal gas；(3) cyst has thin wall + water attenuation + no enhancement of content；(4) abscess has thick irregular enhancing wall + surrounding fat stranding
• Common trap：infected splenic cyst (epidermoid cyst with superinfection) can look identical to abscess → history of known splenic cyst is helpful

06Next step / protocol / appropriateness

影像 protocol 選擇：

• Acute LUQ pain, nontraumatic：CT abdomen/pelvis with IV contrast (portal venous phase mandatory) → rule out infarction, abscess, hemorrhage, pancreatitis
• Suspected embolic splenic infarction：CTA from arch to pelvis → evaluate cardiac source + other organ infarctions + peripheral embolization
• Suspected spontaneous rupture：CT with contrast (arterial + portal venous) → active extravasation → angiography/embolization or surgical consultation
• Incidental SAA on CT：measure largest diameter → if > 2 cm or symptomatic or in woman of childbearing potential → IR or surgical referral
• Suspected splenic abscess：CT with contrast → percutaneous drainage if accessible → blood cultures + echocardiography（endocarditis screen）

07Pitfalls / normal variants

• Zebra spleen / tiger striping：normal heterogeneous enhancement on arterial phase → homogenizes on portal venous phase → NOT infarction
• Accessory spleen (splenunculus)：normal variant, approximately 10–15% of population（autopsy series）→ 常位於 splenic hilum 或 pancreatic tail → can be confused with periportal lymph node or pancreatic tail mass；enhancement pattern 與 spleen 一致 → Tc-99m sulfur colloid / heat-damaged RBC scintigraphy 可確認
• Splenic cleft / lobulation：congenital splenic cleft → mimics laceration on CT → no clinical significance if no hemoperitoneum
• Wandering spleen：congenital absence of splenic ligaments → spleen migrates to pelvis → can undergo torsion → present as pelvic mass with absent spleen in LUQ；torsion 時 CT 顯示 whorled splenic pedicle + non-enhancing spleen
• Autosplenectomy in sickle cell disease：成人 HbSS 患者最常見的脾臟表現 → small, shrunken, diffusely densely calcified spleen on CT；不可誤判為 healed granulomatous disease 或 treated lymphoma
• Gamma-Gandy bodies：punctate siderotic nodules from microhemorrhage in portal hypertension → T2-dark foci on MRI，且在 GRE / SWI 上呈顯著 blooming（low signal） — SWI 為最敏感的 sequence；CT 上偶見 punctate calcification-like foci → normal in portal hypertension context, not pathologic