Fibrolipomatous Hamartoma of the Median Nerve: Pathognomonic MRI Features, Diagnosis, and Clinical Management

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Introduction

Fibrolipomatous hamartoma (FLH) is a rare, benign, tumor-like condition characterized by an abnormal proliferation of mature adipose and fibrous tissue within the epineurium and perineurium of peripheral nerves. Among all peripheral nerves, the median nerve at the wrist and palm is by far the most commonly affected site. Although histologically benign, fibrolipomatous hamartoma can cause significant morbidity due to progressive nerve enlargement and secondary compressive neuropathy.

From a radiologic perspective, magnetic resonance imaging (MRI) plays a pivotal role in establishing a confident diagnosis, often eliminating the need for biopsy. The imaging appearance of fibrolipomatous hamartoma is so distinctive that it is frequently described as pathognomonic, particularly on T1-weighted sequences.

This article provides a comprehensive, literature-based, expert-level review of fibrolipomatous hamartoma, integrating the provided case of a 35-year-old man presenting with wrist pain and swelling, with a detailed discussion of pathophysiology, epidemiology, clinical presentation, imaging features, differential diagnosis, diagnosis, treatment, and prognosis.

Pathophysiology

Fibrolipomatous hamartoma is considered a congenital developmental anomaly rather than a true neoplasm. The hallmark pathological feature is the infiltration of mature adipose tissue and fibrous connective tissue into the epineurium and perineurium, separating and encasing individual nerve fascicles.

This process leads to:

  • Progressive nerve enlargement

  • Distortion of normal fascicular architecture

  • Secondary nerve compression symptoms

Importantly, the lesion does not invade nerve fascicles destructively, which explains its benign biological behavior. The adipose proliferation is interspersed between intact fascicles, producing the characteristic imaging pattern seen on MRI.

FLH is frequently associated with macrodactyly (macrodystrophia lipomatosa), supporting its congenital origin and dysregulated mesenchymal development.

Epidemiology

Fibrolipomatous hamartoma is a rare condition, with the true incidence remaining unknown due to its infrequent diagnosis and occasional asymptomatic presentation.

Key epidemiologic points include:

  • Most commonly diagnosed in children and young adults

  • No strong gender predilection

  • Median nerve involvement in over 80% of cases

  • Less commonly affects the ulnar, radial, plantar, or sciatic nerves

Although congenital, many patients present later in adulthood when progressive nerve enlargement leads to compressive symptoms.

Clinical Presentation

Patients typically present with slowly progressive symptoms, often over months to years.

Common clinical manifestations include:

  • Wrist or palm swelling

  • Palpable soft-tissue mass

  • Pain or discomfort

  • Numbness or paresthesia in the median nerve distribution

  • Symptoms resembling carpal tunnel syndrome

In the presented case, a 35-year-old man reported 3 months of wrist pain and palmar swelling, a classic scenario for adult presentation of fibrolipomatous hamartoma.

Motor deficits are less common but may occur in advanced cases with long-standing compression.

Imaging Features

Magnetic Resonance Imaging (MRI)

MRI is the imaging modality of choice and is usually diagnostic.


Figure 1. Axial MRI of the Wrist

(A) T1-weighted image, (B) T2 STIR image

Imaging Interpretation:

  • Marked enlargement of the median nerve

  • Low-signal intensity nerve fascicles

  • Intervening high-signal fat on T1-weighted images

  • Suppression of fatty signal on STIR sequences

This produces the classic “coaxial cable” appearance, representing thickened nerve fascicles surrounded by fatty tissue.


Figure 2. Axial T1-weighted MRI Pre- and Post-Contrast

(A) Pre-contrast, (B) Post-contrast

Imaging Interpretation:

  • No significant contrast enhancement

  • Confirms benign, non-inflammatory, non-neoplastic nature

  • Contrast primarily useful to exclude malignancy, infection, or vascular malformations

The absence of enhancement strongly supports fibrolipomatous hamartoma.

Ultrasound

Although not provided in this case, ultrasound may demonstrate:

  • Enlarged nerve

  • Hyperechoic fat surrounding hypoechoic fascicles

  • “Honeycomb” pattern in transverse view

Differential Diagnosis

Key differential considerations include:

  1. Intraneural lipoma

    • Discrete encapsulated mass

    • Displaces rather than infiltrates fascicles

  2. Ganglion cyst

    • Cystic lesion

    • No internal fascicular pattern

  3. Neuroma

    • History of trauma

    • Solid enhancement

  4. Vascular malformation

    • Flow voids

    • Marked enhancement

  5. Malignant peripheral nerve sheath tumor

    • Aggressive features

    • Heterogeneous enhancement

    • Infiltrative behavior

The coaxial cable sign on T1 MRI is virtually diagnostic of fibrolipomatous hamartoma.

Diagnosis

Diagnosis is primarily radiologic. Biopsy is strongly discouraged, as it may cause permanent neurologic deficit and is unnecessary when classic imaging findings are present.

In this case, MRI demonstrated:

  • Enlarged median nerve

  • Fatty infiltration between fascicles

  • No contrast enhancement

Final Diagnosis:
Fibrolipomatous hamartoma of the median nerve

Treatment

Management depends on symptom severity:

Conservative Management

  • Asymptomatic or mildly symptomatic patients

  • Observation and clinical follow-up

Surgical Management

  • Indicated for significant neuropathic symptoms

  • Carpal tunnel release and nerve decompression are preferred

  • Complete excision is not recommended due to high risk of neurologic injury

Radical resection does not improve outcomes and may worsen function.

Prognosis

Fibrolipomatous hamartoma is a benign condition with excellent prognosis.

  • No malignant transformation reported

  • Symptoms often stabilize after decompression

  • Recurrence is uncommon when managed appropriately

Long-term outcomes are generally favorable with symptom-based treatment.

Quiz

Question 1. A 35-year-old man presents with wrist pain and palmar swelling. MRI shows an enlarged median nerve with low-signal fascicles surrounded by high-signal fat on T1-weighted images. What is the most likely diagnosis?

A. Ganglion cyst
B. Intraneural lipoma
C. Fibrolipomatous hamartoma
D. Malignant peripheral nerve sheath tumor

Answer: C, Explanation: The classic “coaxial cable” appearance on T1 MRI is pathognomonic for fibrolipomatous hamartoma.

Question 2. Which MRI sequence best demonstrates the diagnostic feature of fibrolipomatous hamartoma?

A. T2-weighted imaging
B. Diffusion-weighted imaging
C. T1-weighted imaging
D. Post-contrast imaging

Answer: C. Explanation: T1-weighted imaging best demonstrates fatty infiltration surrounding nerve fascicles.

Question 3. What is the preferred treatment for symptomatic fibrolipomatous hamartoma of the median nerve?

A. Complete surgical excision
B. Chemotherapy
C. Radiation therapy
D. Surgical decompression

Answer: D, Explanation: Decompression relieves symptoms while preserving nerve function. Complete excision risks permanent damage.

References

[1] E. M. Marom and C. A. Helms, “Fibrolipomatous hamartoma: Pathognomonic on MR imaging,” Skeletal Radiology, vol. 28, no. 5, pp. 260–264, 1999.
[2] M. C. Cavallaro et al., “Imaging findings in fibrolipomatous hamartoma of the median nerve,” AJR, vol. 161, no. 4, pp. 837–838, 1993.
[3] A. Gilet et al., “Fibrolipomatous hamartoma of the median nerve,” Radiology Case Reports, vol. 3, no. 3, p. 195, 2015.
[4] D. Resnick, Diagnosis of Bone and Joint Disorders, 5th ed., Elsevier, 2019.
[5] J. L. Heck et al., “MRI features of peripheral nerve tumors,” Radiographics, vol. 31, pp. 623–642, 2011.
[6] A. Beaman et al., “Benign peripheral nerve sheath tumors,” Radiographics, vol. 24, pp. 1083–1099, 2004.
[7] S. Kransdorf and M. Murphey, Imaging of Soft Tissue Tumors, Lippincott Williams & Wilkins, 2016.

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