High-Yield Board Review: A Posterolateral Chest Wall Lesion

System: Musculoskeletal / Chest Wall

Exam Focus: High-Yield Imaging Review

Key Imaging Pattern: Deep infrascapular mass with interwoven fat streaks and muscle-like soft tissue on CT

1-Clinical Vignette

A 54-year-old man presents with swelling beneath the right scapula and a catching or snapping sensation during arm movements.

• 

• 

2. Board-Style Question

Which diagnosis best explains the location and internal architecture of this lesion?

A. Lipoma

B. Desmoid-type fibromatosis

C. Elastofibroma dorsi

D. Atypical lipomatous tumor

E. Scapulothoracic bursitis

---

3. Correct Answer

C. Elastofibroma dorsi

Elastofibroma dorsi is a benign fibroelastic soft-tissue lesion with a characteristic deep infrascapular location. Its typical imaging appearance combines muscle-like tissue with interspersed linear fat.

• 

• 

Figure 2: Coronal and axial chest CT images demonstrate the right posterolateral chest wall lesion indicated by the arrows. The lesion contains muscle-like soft-tissue attenuation interspersed with low-attenuation fat streaks.

4. Key Imaging Findings

·       Deep infrascapular location, beneath the serratus anterior and latissimus dorsi muscles and adjacent to the chest wall.

·       Predominantly muscle-like soft-tissue attenuation.

·       Interspersed linear fat producing a layered or striated appearance.

·       Indistinct margins blending with adjacent soft tissues.

The combination of characteristic location and interwoven fibrofatty architecture supports elastofibroma dorsi.

5- Diagnostic Reasoning — Why This Diagnosis?

Location + alternating fibrous and fatty tissue is the key diagnostic combination.

Unlike a lipoma, this lesion is not predominantly homogeneous fat. Instead, thin fat streaks are interwoven with muscle-density tissue.

Elastofibroma dorsi occurs more frequently in older women, but male sex does not exclude the diagnosis. Bilateral involvement is common, so the contralateral infrascapular region should also be inspected. Bilateral lesions with the same characteristic architecture further support the diagnosis.

Histologic correlate: The fibrofatty appearance reflects collagenous stroma containing abnormal thickened, fragmented or beaded elastic fibers and mature adipocytes.

6- Why Not the Others?

• Lipoma: Usually predominantly homogeneous fat, rather than muscle-density tissue containing thin fat streaks.

• Desmoid-type fibromatosis: A solid fibrous lesion with variable signal and enhancement. Its characteristic collagen bands are low signal on T1 and T2 and do not enhance; they differ from the T1-bright, suppressible fat streaks of elastofibroma.

• Atypical lipomatous tumor: Usually predominantly fatty, with concerning thick septa or nodular nonfatty components.

• Scapulothoracic bursitis: Produces a fluid-containing distended bursa rather than a solid lesion with interwoven fat. 

7- High-Yield Comparison Table

Diagnosis	Typical architecture	CT/MRI characteristics	Key distinction
Elastofibroma dorsi	Deep infrascapular fibrous tissue interwoven with linear fat	CT: muscle-like attenuation with fat streaks. MRI: muscle-like fibrous tissue with T1-bright fat streaks that suppress	Characteristic location and layered fibrofatty pattern
Lipoma	Predominantly homogeneous fat	Fat attenuation on CT; fat signal on MRI with suppression	Fat is the dominant component
Desmoid-type fibromatosis	Solid fibrous mass; may extend along fascia	Variable T2 signal and enhancement; collagen bands are low signal on T1/T2 and nonenhancing	Collagen bands rather than suppressible fat streaks
Atypical lipomatous tumor	Predominantly fatty mass with thick septa or nonfatty nodules	Fat signal with complex septal or nodular components	Predominantly lipomatous architecture
Scapulothoracic bursitis	Distended scapulothoracic bursa	Fluid attenuation on CT; generally low T1 and high T2 signal	Bursal fluid rather than fibrofatty tissue

8-Sequence-based checkpoint for elastofibroma:

• T1: Muscle-like fibrous tissue with bright fatty streaks.

• Non-fat-suppressed T2: Generally low-to-intermediate signal fibrous tissue with relatively high-signal fatty streaks.

• Fat-suppressed sequences: Fatty streaks suppress. The remaining fibrous tissue signal depends on the sequence and tissue composition; uniform hyperintensity is not a defining feature.

  
  

9- 30-Second Board Recall

• Where? Deep to the muscles near the inferior scapular tip.

• What pattern? Muscle-like tissue interwoven with linear fat.

• Who? More frequent in older women; also occurs in men.

• What else to inspect? The opposite infrascapular region.

• MRI confirmation? T1-bright streaks suppress with fat suppression.

• Management principle? Classic imaging findings can establish the diagnosis without routine biopsy. Atypical appearances require further assessment. Asymptomatic typical lesions may be managed conservatively.

  
  

10-

💡 Radiology Pearl

An indistinct margin alone does not imply malignancy. In elastofibroma dorsi, the characteristic infrascapular location and interwoven fat–fibrous pattern are the decisive clues.

Board trap: Both elastofibroma and desmoid-type fibromatosis may look “banded.” Identify the tissue composing the bands: fat in elastofibroma versus low-signal collagen in desmoid.

Put your heads together. 🤔