Compression neuropathy caused by a lipoma in the fourth finger: a case report
Article information
Abstract
Lipomas are benign tumors originating from adipocytes, and less than 1% of lipomas occur in the fingers. While most lipomas can be managed with observation, those occurring in the fingers can cause symptoms and functional impairment due to the proximity of the subcutaneous fat layer to nerves and blood vessels. Herein, the authors report a case of a patient who experienced finger numbness due to a lipoma extending from the fourth proximal phalanx to the middle phalanx. In cases like this, where initial symptoms are present in the finger but the mass is not palpable, it is essential to actively pursue a diagnosis using ultrasonography or magnetic resonance imaging. Also, in cases of lipomas causing symptoms and functional impairment, early removal may be beneficial for alleviating the patient's symptoms.
Introduction
Lipomas are benign tumors of adipose tissue origin, primarily occurring in the head and neck, shoulders, and back regions. Lipomas on the hands represent 1% to 3.8% of all lipomas and are predominantly located in the thenar eminence or hypothenar eminence, with lipomas occurring on the fingers accounting for less than 1% [1]. While most lipomas can be managed with observation, those occurring in the hand may lead to symptoms and functional impairment due to the proximity of neural and vascular structures to the subcutaneous fat layer. Early removal is considered beneficial for alleviating symptoms and functional impairment caused by lipomas in fingers. To the best of our knowledge, while there have been reports of compressive neuropathy caused by lipomas affecting the median nerve in the flexor tenosynovium of the hand and the superficial radial nerve in the anatomical snuff box, there have been no specific reports of compressive neuropathy due to lipomas in the fingers, except for a case series in 2022 that documented such cases in the index finger [2]. The authors report a case of a patient presenting with numbness in the 4th finger due to a lipoma located in the proximal interphalangeal (PIP) joint extending to the proximal phalanx and middle phalanx.
Case report
This report was approved from the Institutional Review Board of Dong-A University Hospital (No. DAUHIRB-24-029). Written informed consent was obtained from the patient for the publication of this report including all clinical images.
A 63-year-old man has complained of numbness in the radial aspect of 4th finger for the past 10 years. He has a history of cerebral infarction and heart valve disease, requiring warfarin therapy for the past 15 years. At that time, there were no palpable masses specifically on the 4th finger, and the numbness worsened over the past 2 years. He underwent physical therapy and injection therapy for suspected carpal tunnel syndrome (CTS) at another hospital. However, he continued to experience persistent numbness in the distal aspect of the 4th finger, accompanied by palpable masses in the PIP joint. Nerve conduction studies conducted at the previous hospital did not reveal any significant findings. Subsequently, due to a rapid increase in the size of the mass, he was referred to our hospital to evaluate the possibility of pseudoaneurysm formation due to bleeding tendency from warfarin use and to determine whether there was malignant tumor formation.
During the examination at the time of his visit, a mobile, soft mass was palpated on the radial and volar aspect of the PIP joint of the right 4th finger, with no tenderness but worsening numbness. The joint range of motion was not restricted, and no inflammatory changes such as ulceration, pigmentation, erythema, or heating sensation were observed on the skin above the mass. X-rays revealed increased soft tissue density without evidence of bony involvement (Fig. 1), while ultrasound showed a mass extending from the proximal phalanx to the base of the middle phalanx in the subcutaneous tissue (Fig. 2). Magnetic resonance imaging demonstrated a lesion measuring 2.8×0.64 cm with high signal intensity on T1-weighted images and low signal intensity on T2-weighted images, resembling subcutaneous fat tissue. Fat-suppressed images showed low signal intensity suggestive of a lipomatous lesion, with no evidence of bony invasion (Fig. 3). Also in axial images, it was observed that the mass compressed the digital nerve. The proximal portion of the mass shows an enlargement of the digital nerve with an axial area of 3.73 mm2, while at the mid-level of the mass, the nerve area is compressed to 1.23 mm2 (Fig. 4).
Simple radiograph showing increased soft tissue density around the right fourth finger.
Ultrasound from the radial side (A) and volar side (B) show a mass extending from the proximal phalanx head to the middle phalanx shaft in subcutaneous tissue.
On magnetic resonance imaging, a lesion measuring 2.8×0.64 cm was observed, showing high signal intensity on T1-weighted images (A) and low signal intensity on T2-weighted images (B), resembling subcutaneous fat tissue. (C) The lesion exhibited low signal intensity on fat-suppressed images, suggesting a fat-containing lesion. No bony involvement was identified.
In the axial view of the magnetic resonance imaging, the mid-level of the mass (A) shows compression of the digital nerve, while at the proximal level (B), the nerve appears enlarged. The dotted circles indicate the digital nerves.
Surgery was performed under general anesthesia due to the inability to perform brachial plexus block caused by warfarin use. A curved incision was made on the radial aspect of the hand centered on the PIP joint. Upon exploration, a mass surrounded by soft tissue resembling normal adipose tissue, with clear margins and encapsulated by a membrane, was observed. The mass was observed to be adherent to the epineurium of the nerve, and dissection was performed. Additionally, the mass was noted to be white in color, indicating degeneration. There was no evidence of involvement of the periosteum or bone marrow. Marginal excision was performed, dissecting and removing the adherent portion along with the membrane, ensuring the integrity of the digital nerve, and decompression was performed on surrounding fibrous tissues (Fig. 5). Histopathological examination revealed lobulated adipose tissue surrounded by thin fibrous tissue measuring 3.1×1.9 cm and 1.5×0.8 cm. The patient showed improvement in numbness of the hand from the first day after surgery, with complete resolution of numbness observed at the 4-week follow-up. At the 1-year follow-up visit, the patient reported complete resolution of discomfort related to numbness and the mass.
(A) A well-defined, encapsulated mass was observed in the subcutaneous tissue, surrounded by soft tissue resembling normal adipose tissue. (B) A marginal excision of the lesion was performed, with dissection and removal of the tissue that adhered to the capsule. (C) The digital nerve was identified, and decompression was performed on the surrounding adhered fibrous tissue.
Discussion
Lipomas, along with lipofibromatous hamartomas, angiomas, and other non-neurogenic tumors, constitute approximately 16% of soft tissue mesenchymal tumors [3]. According to the 2020 World Health Organization classification of soft tissue tumors, adipocytic tumors are categorized into 15 types: lipoma, neural lipoma, lipoblastoma, angiolipoma, myolipoma of soft tissue, chondroid lipoma, spindle cell/pleomorphic lipoma, hibernoma, among others [4].
Lipomas are rarely found in the hand and extremely rarely in the fingers. Among lipomas occurring in the hand, 5% can cause neurological symptoms depending on their location, potentially leading to neuropathy [2]. Neurological symptoms are not related to the size of the tumor, but rather the tumor's position relative to the nerve plays a significant role in the development of these symptoms. According to Chen et al. [5], out of 779 patients with CTS, only three cases were reported to be caused by lipoma within the carpal tunnel.
Lipomas occurring in the fingers need to be differentiated from ganglion cysts, giant cell tumors of the tendon sheath, and neurilemmomas. These lesions can be distinguished using magnetic resonance imaging. Ganglion cysts and neurilemmomas appear hypointense on T1-weighted images, hyperintense on T2-weighted images, and show non-suppressed hyperintensity on short tau inversion recovery images. Giant cell tumors of tendon sheath generally appear hypointense on both T1- and T2-weighted images [6]. It can be also differentiated with ultrasound. The ultrasound appearance of a lipoma is generally a hyperechoic mass without posterior acoustic enhancement; however, it can also appear hypoechoic or isoechoic in some cases. Additionally, because the subcutaneous fat layer of the finger is thin, it is not easy to compare the echo difference between the surrounding fat layer and the mass, making differential diagnosis difficult.
According to a study analyzing 13 cases of lipomas in the hand, the main symptoms included a palpable mass, swelling, pain, muscle weakness, and functional impairment [7]. Clinical symptoms in the fingers can vary from a palpable lump to restricted movement. Ramirez-Montaño et al. [8] reported that lipomas larger than 50 mm significantly affected the range of motion in the interphalangeal joints of the fingers. It is recommended to remove lipomas in the hand early upon detection because they can gradually increase in size, causing pain, sensory deficits, and motor impairment, unlike in other parts of the body [9].
The patient in this case reported numbness even before the discovery of the mass in the finger. This led to a misdiagnosis of CTS at another hospital, where treatment was provided for that condition. While numbness occurring in the radial volar area of the 4th finger could be attributed to CTS, if it is confined to a single finger, differential diagnosis should consider lipomas, angiolipomas, giant cell tumors, ganglion cysts, and hemangiomas. When symptoms are present but the mass is not palpable, as in the early stages of this case, active use of ultrasound or magnetic resonance imaging may be necessary for diagnosis [7]. Since fingers have relatively dense tissue and nerves and blood vessels nearby, even small masses can cause early symptoms such as numbness, cold sensation, and swelling. Without fundamental removal of the mass, improvement in symptoms is difficult to expect, and chronic neuropathic pain unresponsive to analgesics and permanent nerve function impairment may occur [7]. Additionally, recurrence of lipomas after excision is rare, at about 5%, with incomplete removal being the primary cause [10]. In conclusion, if a lipoma confined to the finger is diagnosed, early surgical removal of the mass is advantageous, as demonstrated in this case.
Notes
Conflicts of interest
The authors have nothing to disclose.
Funding
None.