Introduction

A 35-year-old man presents with progressive wrist pain, swelling in the palmar wrist, and intermittent numbness. Initial concern may include a ganglion cyst, nerve sheath tumor, or tendon pathology. However, advanced medical imaging reveals a far rarer diagnosis: Fibrolipomatous Hamartoma (FLH) of the median nerve.

This uncommon benign lesion is one of the most fascinating entities in radiology interpretation because it often demonstrates pathognomonic MRI findings that allow diagnosis without biopsy. For clinicians, radiologists, orthopedic surgeons, and imaging professionals, understanding FLH is crucial because it can mimic more aggressive pathology while requiring a very different management strategy.

In this comprehensive guide, we review:

Pathophysiology
Epidemiology
Clinical presentation
MRI, CT scan, diagnosis, X-ray, and ultrasound findings
Differential diagnosis
Stepwise diagnostic workflow
Treatment strategies
Prognosis
Quiz section for learning retention

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What Is Fibrolipomatous Hamartoma?

Fibrolipomatous hamartoma (also called lipofibromatous hamartoma) is a rare benign fibro-fatty overgrowth involving peripheral nerves. It most commonly affects the median nerve, especially at the wrist and carpal tunnel.

The lesion consists of:

Mature adipose tissue proliferation
Fibrous tissue infiltration
Expansion of the epineurium and perineurium
Separation of normal nerve fascicles by fat

Rather than being a true neoplasm, FLH is considered a congenital or developmental overgrowth disorder.

Why This Lesion Matters in Medical Imaging

Many wrist masses lead to concern for malignancy or urgent surgery. However, FLH often has classic imaging signs that allow confident noninvasive diagnosis.

This means:

Fewer unnecessary biopsies
Better surgical planning
Reduced patient anxiety
More accurate radiology interpretation
Improved hand function preservation

Epidemiology

FLH is rare, and the exact incidence remains unknown.

Key Facts

Feature	Data
Most common nerve	Median nerve
Typical site	Wrist/carpal tunnel
Age at presentation	Childhood to middle age
Sex predilection	No clear dominance
Associated condition	Macrodactyly

Although many lesions are congenital, symptoms may not appear until adulthood when the mass enlarges or compresses adjacent structures.

Pathophysiology

The precise cause remains uncertain, but several mechanisms are proposed:

1. Congenital Malformation

Abnormal mesenchymal tissue growth around a developing nerve.

2. Chronic Mechanical Stress

Repeated motion at the wrist may worsen symptoms.

3. Fibrofatty Proliferation

Mature fat infiltrates between fascicles, producing nerve enlargement.

The result is progressive distortion of nerve architecture and compressive neuropathy.

Clinical Presentation

Symptoms depend on lesion size and degree of nerve compression.

Common Symptoms

Wrist pain
Palmar swelling
Tingling in the thumb, index, and middle fingers
Numbness
Weak grip strength
Night symptoms similar to carpal tunnel syndrome
Slowly enlarging palpable mass

Typical Storytelling Scenario

A patient is treated repeatedly for “carpal tunnel syndrome,” but symptoms worsen despite splinting. MRI later reveals an enlarged median nerve with internal fat—classic FLH.

Imaging Features: Core Diagnostic Section

MRI Diagnosis (Most Important)

MRI is the best modality for diagnosis.

Pathognomonic Signs

Axial Images: “Coaxial Cable Sign”

Low-signal nerve fascicles are surrounded by high-signal fat, resembling a bundled electrical cable.

Coronal/Sagittal Images: “Spaghetti Sign”

Elongated serpiginous fascicles are separated by fat.

Signal Characteristics

Sequence	Appearance
T1	High signal fat with low signal fascicles
T2	Variable
STIR	Fat suppression improves fascicle conspicuity
Post-contrast	Usually minimal or no enhancement

Figures from the Provided Case

Figure 1. Axial T1 Weighted MRI

Shows enlarged median nerve at the wrist with internal high T1 signal fat surrounding low-signal fascicles. This classic appearance strongly suggests fibrolipomatous hamartoma.

Figure 2. Axial T2 STIR MRI

Fat suppression reduces the signal from adipose tissue and better delineates thickened fascicles within the enlarged nerve. Useful for confirming architecture and excluding edema.

Figure 3. Axial T1 Pre-Contrast MRI

Demonstrates persistent fatty infiltration without aggressive soft tissue features.

Figure 4. Axial T1 Post-Contrast MRI

No meaningful internal enhancement. This supports benign fibro-fatty proliferation rather than malignant peripheral nerve tumor or abscess.

CT Scan Diagnosis

Although MRI is preferred, a CT scan diagnosis can be highly useful when MRI is unavailable or contraindicated.

CT Findings

Enlarged nerve bundle
Low attenuation fat surrounding fascicles
No bone destruction
No aggressive soft tissue invasion

CT is particularly useful for:

Preoperative anatomy
Assessing osseous remodeling
Emergency settings when MRI access is delayed

X-Ray Findings

Plain radiographs are often normal but may show:

Soft tissue fullness
Macrodactyly if associated
Chronic remodeling from mass effect

Ultrasound Findings

High-resolution ultrasound can be excellent in experienced hands.

Findings

Enlarged nerve
Hypoechoic fascicles
Echogenic interfascicular fat
Dynamic compression in the carpal tunnel

Ultrasound is cost-effective and ideal for follow-up.

Differential Diagnosis

Because wrist masses are common, distinguishing FLH is essential.

Diagnosis	Key Difference
Intraneural lipoma	Focal encapsulated fat mass, not fascicular infiltration
Schwannoma	Enhancing solid nerve sheath tumor
Neurofibroma	Fusiform soft tissue mass
Ganglion cyst	Fluid lesion, T2 bright
Vascular malformation	Flow voids/enhancement
Malignant peripheral nerve sheath tumor	Heterogeneous, invasive, painful

Diagnosis Workflow

Step 1: Clinical Exam

Assess:

Sensory loss
Median nerve distribution symptoms
Mass palpation
Weak thumb opposition

Step 2: Initial Imaging

X-ray if mass is suspected
Ultrasound for superficial lesions

Step 3: MRI

Best single test for definitive diagnosis.

Step 4: Electrophysiology

Nerve conduction studies if compression symptoms exist.

Step 5: Surgical Referral

For progressive symptoms or severe neuropathy.

Is a biopsy needed?

Usually no.

When MRI findings are classic, biopsy may risk nerve injury and is often unnecessary.

Biopsy is reserved for:

Atypical enhancement
Rapid growth
Diagnostic uncertainty
Suspicion of malignancy

Treatment Options

Management depends on symptoms.

Conservative Management

Best for mild or incidental lesions.

Observation
Wrist splinting
Activity modification
Anti-inflammatory treatment
Periodic imaging

Surgery

Used when symptoms progress.

Common Procedures

Carpal tunnel release
External neurolysis
Debulking (select cases)
Rare nerve grafting

Important Note

Complete excision can cause a permanent neurologic deficit because fascicles traverse the lesion.

Therefore, decompression—not aggressive resection—is often preferred.

Prognosis

FLH is benign and does not metastasize.

Outcomes

Stable for years in many patients
Symptoms improve after decompression
Recurrence possible if residual compressive tissue remains
Long-term neurologic deficits may persist if delayed treatment

Early diagnosis improves functional outcomes.

Emergency Diagnosis: When It Matters

Although FLH is not usually an emergency, urgent evaluation is appropriate when patients have:

Rapid neurologic decline
Acute severe pain
New weakness
Concern for compartment syndrome
Suspected malignancy

In such settings, prompt medical imaging prevents mismanagement.

Key Takeaways

Fibrolipomatous hamartoma is a rare benign fibro-fatty lesion of peripheral nerves.
The median nerve at the wrist is the classic location.
MRI often shows pathognomonic coaxial cable and spaghetti signs.
A CT scan diagnosis can support the case when an MRI is unavailable.
A biopsy is usually unnecessary if the imaging is classic.
Treatment focuses on decompression rather than total excision.

FAQ Section

Is fibrolipomatous hamartoma cancer?

No. It is a benign lesion and does not metastasize.

Can it be cured?

Symptoms can improve significantly after decompression surgery, but structural changes may remain.

Is MRI always necessary?

MRI is the most accurate test, though ultrasound and CT can assist.

Can it cause carpal tunnel syndrome?

Yes. Median nerve involvement at the wrist commonly produces carpal tunnel symptoms.

Is recurrence common?

Symptoms may recur if compression persists, but malignant transformation is exceptionally rare.

Quiz

Question 1. Which nerve is most commonly affected by fibrolipomatous hamartoma?

A. Radial nerve
B. Median nerve
C. Sciatic nerve
D. Femoral nerve
E. Axillary nerve

Correct Answer: B. Median nerve. Explanation: The median nerve, especially at the wrist/carpal tunnel, is the classic site.

Question 2. Which MRI sign is most characteristic on axial imaging?

A. Sunburst sign
B. Double line sign
C. Coaxial cable sign
D. Crescent sign
E. Halo sign

Correct Answer: C. Coaxial cable sign. Explanation: Thickened low-signal fascicles surrounded by fat mimic an electrical cable.

Question 3. Preferred surgical principle in symptomatic FLH is:

A. Radical excision
B. Amputation
C. Chemotherapy
D. Decompression with nerve preservation
E. Radiation therapy

Correct Answer: D. Explanation: Because normal fascicles traverse the lesion, decompression is safer than total excision.

Summary Table

Category	Key Point
Nature	Benign fibro-fatty nerve lesion
Common Site	Median nerve
Best Test	MRI
CT Role	Alternative/anatomy
Typical Symptom	Carpal tunnel-like neuropathy
Treatment	Decompression
Prognosis	Generally favorable

Fibrolipomatous Hamartoma of the Median Nerve: MRI & CT Scan Diagnosis, Radiology Interpretation, and Best Treatment Guide for Rare Imaging Cases