A 20-year-old woman presented with a large mass in the volar aspect of the left wrist and hand, which had been increasing over the past two years. She had paresthesia in the 2nd, 3rd and 4th fingers. Lymph node tumefaction was not detected, nor was any sign of neurofibromatosis. There was no history of trauma.
Magnetic resonance imaging (MRI) demonstrated a fusiform enlargement of the median nerve at the level of the distal forearm, wrist and volar aspect of hand, extending to the digital branches. The tumour measured 6 x 2.5 cm in its transverse diameters and 17 cm in its length. T1 and T2 weighted images (WI) showed tubular low-intensity structures encased in high signal tissue representing fat, which homogeneous drop in signal intensity on fat suppression images. On axial sequences the lesion demonstrated a “coaxial cable-like” appearance while on coronal and sagittal images a “spaghetti string” appearance was noted. This constellation of findings is pathognomonic of fibrolipomatous hamartoma.
Fibrolipomatous hamartoma is a benign tumour composed of hypertrophied fibrofatty tissue intermixed with nerve tissue, usually confined to the nerve sheath. This lesion is also known as neural fibrolipoma, lipofibromatous hamartoma, perineural lipoma and intraneural lipoma [1-4].
The aetiology of this disorder has not been definitively clarified. Various hypotheses were suggested: congenital origin, growth by nerve irritation, inflammation or prior trauma [2, 3, 5].
The age of presentation is typically before 30 years of age, often in early childhood and less commonly in early adult age [1-4, 6, 7].
Males and females are equally affected, and there is no familial predisposition [1].
The median nerve is the most commonly affected nerve (80-85% of cases). However, involvement of others nerves has been reported [1-3, 8-10].
Patients typically present a soft, slowly enlarging mass on the volar wrist or distal forearm [4], often present since infancy. It may be asymptomatic, or may produce neurologic symptoms, due to nerve compression, in the affected nerve distribution, such as pain, numbness, diminished sensibility and strength or carpal tunnel syndrome [1, 2, 3, 5].
Frequently fibrolipomatous hamartoma is associated with macrodactyly (20-67% of cases) [1, 2, 4], which results in bony overgrowth, and fat deposition in subcutaneous tissue, tendons, muscles, and nerves [3].
Plain film is non-specific and may be normal in patients without macrodactyly or may show a soft tissue mass related to the fibrofatty tissue [1].
At ultrasound (US) it appears as a soft tissue lesion with smooth round hypo-or anechoic bands (fascicles) surrounded by hyperechoic tissue (fatty tissue) [1, 2, 4, 10]. Spectral Doppler will demonstrate no flow within the mass [2].
Computed tomography (CT) shows fusiform nerve enlargement which is caused by fatty tissue interposed among serpentine or tubular structures of soft tissue density [2, 3].
Although the sonographic and CT features are characteristic of the lesion [10], MRI is the preferred modality for diagnosis, because MRI features are considered pathognomonic [2]. They consist of longitudinal cylindrical linear or serpiginous bands, about 3 mm in diameter, with low signal intensity on T1 and T2-WI, representing nerve fascicles and surrounding fibrous tissue, surrounded by fat, which appears as high intensity on T1 and T2-WI, with decrease of high signal on fat suppressed images. This leads to a “coaxial cable-like” appearance on axial images and a “spaghetti string” appearance on coronal images [1-3, 6, 7, 10].
Associated intramuscular fat deposition has been described, related to nerve injury and muscle denervation, macrodactyly or in the absence of macrodactyly [3].
Fibrolipomatous hamartoma of the median nerve
Based on the MRI images (coronal and axial views) provided by the patient, the following features are noted:
1. A soft tissue mass signal is observed on the palmar side of the left wrist, showing progressive enlargement;
2. Irregular fatty components within the lesion (high signal on T1- and T2-weighted images, with decreased signal on fat-suppressed sequences);
3. Between areas of high-signal fat tissue, irregular or “band-/tube-like” low-signal bundles can be seen, resembling a “coaxial cable” or “spaghetti-like” appearance;
4. Thickening of soft tissue around the nerve, suggesting an interweaving of fibrofatty components with the nerve bundles;
5. No obvious lymph node enlargement or bony destruction/remarkable bony abnormalities are evident.
Overall, these findings are consistent with the typical imaging features of a “fibrolipomatous hamartoma” (fibrolipomatous hamartoma) causing nerve enlargement.
Imaging features: Shows a mixture of fatty signals and band-/tube-like soft tissue bundles, often accompanied by nerve enlargement, with a typical “coaxial cable” or “spaghetti-like” appearance. It frequently occurs in younger patients, commonly in the carpal tunnel or palmar wrist area.
Clinical characteristics: May cause nerve compression symptoms such as paresthesia or numbness in the fingers, and typically grows slowly.
Imaging features: Primarily composed of fatty tissue without clear imaging evidence of intertwined nerve bundles; usually no significant nerve stimulation symptoms.
Clinical characteristics: Generally slow-growing, often presenting as a painless soft tissue mass.
Imaging features: Tumor typically appears as a homogeneous or mixed soft tissue density/signal, often aligned with the nerve pathway, but usually does not contain significant fat components.
Clinical characteristics: May cause corresponding nerve compression symptoms, but the lack of substantial fat content on imaging is inconsistent with this case.
Imaging features: Primarily cystic lesions with fluid signal (high signal on T2), lacking fatty components; commonly located around joints or tendon sheaths.
Clinical characteristics: May appear in the wrist or hand, often palpable with a fluctuant or cystic feel.
Considering the patient is a young female with a slowly enlarging palmar wrist mass, associated sensory disturbances (numbness in fingers 2–4), and MRI findings showing a “fat + fibrous tissue + nerve bundle” mixed signal, the most likely diagnosis is Fibrolipomatous Hamartoma.
If there are still clinical doubts, further pathological examination can be performed to confirm the diagnosis.
Treatment Strategy:
1. Conservative Management: In cases where the mass is relatively small and symptoms are mild, observation with regular imaging follow-ups may be considered. If symptoms can be alleviated by wrist supports, physical therapy, or nerve mobilization techniques, surgical intervention may be deferred.
2. Surgical Intervention: If marked nerve compression symptoms develop (e.g., persistent numbness, pain, reduced muscle strength) or the mass significantly enlarges and affects hand function, surgical exploration with nerve decompression or partial resection may be indicated.
Rehabilitation and Exercise Prescription (FITT-VP Principle Example):
1. Frequency: Early phase: 2–3 times per week under the guidance of a qualified therapist for functional training; mid-to-late phase: can be increased to 3–5 times per week based on recovery status.
2. Intensity: Begin with light, pain-free activities (e.g., passive finger movements, gentle wrist stretching), avoiding excessive stress or aggravation of nerve compression; gradually increase resistance and range of motion as recovery progresses.
3. Time: Start with 10–15 minutes per session; gradually extend to 20–30 minutes based on tolerance; ensure adequate rest intervals.
4. Type: Includes finger joint flexibility training (e.g., using resistance bands or soft ball squeezing), light wrist and forearm resistance exercises (e.g., hand grippers or small dumbbells), and emphasis on nerve gliding techniques to relieve pressure-related symptoms.
5. Progression: As symptoms improve and wrist/hand strength increases, gradually add load and complexity to the exercises. If symptoms recur or worsen, seek medical advice promptly and adjust the plan.
This report is based solely on the clinical and imaging information provided and is intended to serve as a reference for clinical decision-making. All diagnostic and treatment decisions should be made in conjunction with the patient’s actual condition and determined by a qualified physician. This report is not a substitute for in-person consultation and examinations. If you have further questions, please consult a specialist.
Fibrolipomatous hamartoma of the median nerve
