Focal hand lesions: review and radiological approach

Chau Hung Lee Ankit Tandon Focal hand lesions are commonly encountered in clinical practice and are often benign. Magnetic resonance (MR) imaging is the imaging modality of choice in evaluating these lesions as it can accurately determine the nature of the lesion, enhancement pattern and exact location in relation to surrounding tissues. However, while MR features of various soft tissue lesions in the hand have been well described, it is often still difficult to differentiate between benign and malignant lesions. We review the MR imaging features of a variety of focal hand lesions presenting at our institution and propose a classification into benign, intermediate grade (histologically benign but locally aggressive with potential for recurrence) and frankly malignant lesions based on MR findings. This aims to narrow down differential diagnoses and helps in further management of the lesion, preoperative planning and, in cases of primary malignancy, local staging. Teaching Points Hand lesions are often benign and MR is essential as part of the workup. MR features of various hand lesions are well described but are often non-specific. Certain MR features may help for the diagnosis but histological examination is usually required. We aim to classify hand lesions based on MR features such as margin, enhancement and bony involvement. Classifying these lesions can help narrow down differential diagnoses and aid management. - Most soft tissue lesions in the hand are benign [1]. Imaging is often required to determine the nature of the lesion. Plain radiography has limited utility but is useful in demonstrating calcification. Ultrasound is a cheap and relatively quick method for determining the cystic or solid nature of the lesion. Magnetic resonance (MR) is the imaging modality of choice as it can accurately determine the nature of the lesion, enhancement pattern and exact location in relation to surrounding tissues given its high contrast and spatial resolution. However, while MR features of various soft tissue lesions in the hand have been well described, preoperative diagnosis of these lesions is often difficult, and even distinguishing benign from malignant lesions remains challenging. We review the MR imaging features of a variety of hand lesions presenting at our institution and propose a classification into benign, intermediate grade (histologically benign but locally aggressive with potential for recurrence) and frankly malignant lesions based on MR findings. This aims not just to narrow down differential diagnoses but also to help in further management of the lesion in terms of preoperative planning, and for cases of primary malignancy, local staging and prognosis. Imaging technique At our institute, MR imaging is performed on a 1.5- or 3-T scanner. Several technical factors need to be considered to get the best images of the hand and wrist. Important technical factors to consider are patient positioning, choice of coil and sequences. Based on the lesion location and extent of coverage required, patients are scanned using an extremity, wrist or best-fit surface coil. Whenever high-resolution imaging using thin slices and a small field of view (FOV) is critical, surface coils are preferred. Patients are routinely scanned in the supine position with arm by the side. Sometimes patients are scanned in the superman position, with the patient lying prone and the arms above their head. Meticulous positioning is important to bring the region of interest to isocenter. When the region of interest is close to the periphery of the coil, auto shimming is used. Skin markers are used to localise small lumps. The routinely used sequences at our institute include T1weighted (T1w) sequences in the axial and coronal planes, T2weighted fat-saturated (T2w-FS) or short tau inversion recovery (STIR) sequences in the axial plane and T2-weighted (T2w) sequences without fat saturation in either the sagittal or coronal plane. A gradient-echo (GRE) sequence is also acquired, which is particularly useful if a vascular lesion or giant-cell tumour of the tendon sheath is suspected. Postcontrast T1w-FS sequences with intravenous gadolinium compounds are acquired in all patients unless contraindicated. Routine FOV of 1620 cm, slice thickness of 4.0 mm and matrix of at least 512256 is used, although when higher resolution imaging is critical, a smaller FOV of 812 cm and thinner slice thickness of 1.53.0 mm are preferred. Benign lesions Ganglion cysts are the most common lumps encountered in the hand and wrist region [2]. They tend to occur in young adults and are three times more frequent in females. They are thought to represent degeneration of connective tissue caused by chronic irritation [3]. The most common location is in the dorsum of the wrist where they usually arise from the scapholunate joint. Less typical sites include the volar aspect of the wrist from the radio-scaphoid or scapho-trapezial joint, at the metacarpophalangeal joint in relation to flexor tendons and distal interphalangeal joints [4]. MR shows a wellcircumscribed unilocular or multilocular lesion of fluid signal, although the signal may vary depending on the amount of proteinaceous contents (Fig. 1). Mild rim enhancement of the capsule may be seen, but there is usually no enhancement of internal contents. Differential diagnoses include synovial cysts and other cystic lesions such as epidermal cysts. Epidermal cyst Epidermal cysts are common hand lesion resulting from proliferation of epidermal cells within a confined space in the dermis. They can be congenital, a result of occlusion of the follicles by adjacent inflammation or tumour, or associated with human papilloma virus infection [5]. True epidermal cysts result from implantation of epithelial squames into the dermis because of trauma. MR shows a well-circumscribed lesion of fluid signal in the dermis or subdermis (Fig. 2). However, signal on the T2w sequence may be variable depending on the amount of internal keratin debris [6]. Rim enhancement can be seen. Lack of central enhancement is key to distinguish epidermal cysts from more sinister lesions such as neurogenic tumours or sarcomas, particularly if heterogeneous signal is present because of internal debris. They may also be mistaken for ganglion cysts if located close to the joint or tendon sheath. Fibroma of the tendon sheath Fibromas of the tendon sheath (FTS) are uncommon lesions thought to be a reactive fibrosis. It has a peak incidence at 20 50 years old, is three times more common in males, and 82 % of them occur in the hand and wrist region [7, 8]. The low signal on all MR pulse sequences expected of a fibrous lesion is not always seen. FTS are generally well defined and of low signal on T1w sequence. Signal intensity on T2w sequence and contrast enhancement is more varied and heterogeneous (Fig. 3), likely reflecting varying proportions of fibrous and cellular tissue [9]. Differential diagnoses includ (...truncated)