Comparing Ultrasound with Magnetic Resonance Imaging in the Evaluation of Subungual Glomus Tumors and Subungual Myxoid Cysts

Abstract

Introduction

Subungual myxoid cysts and subungual glomus tumors demonstrate characteristic features on magnetic resonance imaging (MRI) and ultrasound (US). It is not yet well-established whether US is congruent to MRI in diagnostic evaluation of these subungual lesions.

Methods

Participants with clinical suspicion for subungual glomus tumors or subungual myxoid cysts were recruited. After clinical evaluation, participants underwent radiography, MRI, and US plus biopsy, aspiration, or excision where possible. Differential diagnoses were revised after review of imaging, and imaging findings were compared to definitive diagnosis by pathology, aspiration, or clinical course.

Results

All lesions were visible on both US and MRI and size estimates agreed between the two modalities. US and MRI findings of subungual glomus tumors and subungual myxoid cysts agreed with their known respective imaging characteristics.

Conclusions

Diagnosis of subungual myxoid cysts and subungual glomus tumors agreed between US and MRI. We provide sample MRI and US imaging parameters for optimal evaluation of subungual myxoid cysts and glomus tumors. We demonstrate that subungual MRI evaluation can be performed without special equipment, allowing for evaluation by most radiology departments. Lastly, US is user-dependent and may be non-inferior for a sonographer familiar with subungual US.

Tumors that arise from the space below the nail plate, called the subungual space, are rare. Subungual tumors can be sensitive or painful and may be either benign or malignant, so medical workup should be pursued to reach a diagnosis. Myxoid cysts and glomus tumors are both examples of benign subungual tumors. Medical imaging, such as ultrasound (US) and magnetic resonance imaging (MRI), can be useful in characterizing and diagnosing disease within the small subungual space. MRI, however, is often less accessible and more time-consuming when compared to US.

This study, conducted at the University of Washington in Seattle, Washington, USA, aims to evaluate how US and MRI compare in examining these subungual masses. Patients were recruited by a dermatologist if a subungual glomus tumor or myxoid cyst was suspected. These patients underwent different types of medical imaging, and images were reviewed by a radiologist. We found that diagnosis of subungual myxoid cysts and subungual glomus tumors agreed between US and MRI. We discuss that US is user-dependent and that collaboration between dermatology and radiology is key to producing the best possible image quality. We provide sample MRI parameters for a high-quality image of a subungual tumor.

Introduction

Subungual glomus tumors and subungual myxoid cysts are two examples of benign subungual tumors. Glomus tumors, hamartomas of the highly vascular glomus body, account for 1.0–4.5% of all hand tumors and may present with the triad of cold temperature sensitivity, severe pain, and point tenderness (Love’s test) [1, 2]. Although some distinguish ganglion cysts of the distal digit from myxoid cysts by the presence of a synovial lining [3], others consider myxoid and ganglion cysts synonymous and result from extravasation of joint fluid into the tissue [4]. Myxoid cysts most often manifest between the distal interphalangeal (DIP) joint and proximal nail fold with trough-like changes in the dorsal surface of the nail plate but can present beneath the nail plate [5]. Myxoid cysts are also commonly associated with DIP joint osteoarthritis.

Accurate diagnosis is key, as subungual masses can be concerning for patients, the differential diagnoses include malignancy, and the treatment of subungual glomus tumors and myxoid cysts differs. If one were certain that one was dealing with a glomus tumor, imaging might not be necessary. However, the clinical presentation of a subungual myxoid cyst may be identical to that of a glomus tumor or other subungual entities. Since a subungual myxoid cyst may arise due to joint pathology in the distal interphalangeal joint, the definitive treatment of such a cyst may be beyond the expertise of most dermatologists and require a referral to a hand surgeon. In the clinically indeterminate cases, it is helpful that subungual myxoid cysts and glomus tumors produce characteristic imaging features as described in the literature. MRI is superior in evaluation of soft tissues and is helpful for planning biopsy/excision. However, MRI is expensive, time-consuming, and may not be available in all localities. US has the potential to increase accessibility and speed of diagnosis of subungual masses at a lower cost. As such, we seek to compare US to MRI in the diagnosis of digital subungual glomus tumors and myxoid cysts. Because US has the potential to detect smaller lesions, we also seek to assess whether US is useful in characterizing lesion size and surrounding tissue involvement to assist surgical planning.

Materials and Methods

Participants with clinical suspicion for a subungual glomus tumor or myxoid cyst after evaluation by a University of Washington Medical Center (UWMC) attending dermatologist (P.F. or A.K.S.) were recruited between July 2018 and April 2021. After enrollment into the study, participants underwent X-ray (except for one participant), MRI, and US with doppler of their subungual masses. One participant underwent computerized tomography (CT) in lieu of MRI. When possible, participants underwent biopsy or excision depending on their clinical course. Differential diagnoses were revised after review of radiology and images were rereviewed by one attending radiologist (M.L.R.) within the Department of Radiology. Recommended US and MRI parameters for imaging of subungual masses are summarized below in Tables 1–3. All participants provided their consent for inclusion and this study was approved by the University of Washington Institutional Review Board (IRB).

Table 1.

Recommended ultrasound (US) parameters for evaluation of subungual masses

Tool:	Small parts probe
Frequency:	7–15 MHz
Technique:	• Sometimes masses are only well-seen if the ultrasound beam is exactly perpendicular to the lesions. However, by carefully positioning the probe in real-time, one can obtain images in all desired imaging planes • The imager should take care to include the nail fold on the images, to aid the clinician in the best surgical approach • If a mass is visualized, image dimensions can be measured directly off the US images

Table 3.

Sample MRI pulse sequence protocol for a 3.0 Tesla MR scanner to image subungual masses

Sequence	Plane	Pixel size	Matrix	ST/gap	TR	TE	TI	ETL
T1W SE	Axial	0.25	320 × 320	2.5/0.25	685	20	NA	5
T1W SE	Coronal	0.25	400 × 400	2.5/0.25	500	20	NA	5
T2W SPAIR	Axial	0.3125	256 × 256	2.5/0.25	5,235	80	NA	17
T2W SPAIR	Sagittal	0.3125	512 × 512	2.5/0.25	3,000	80	NA	17
STIR	Coronal	0.416	240 × 240	2.5/0.25	3,000	30	220	16
T1W FS	Axial	0.25	320 × 320	2.5/0.25	780	20	NA	5
T1W FS PG	Axial	0.25	320 × 320	2.5/0.25	780	20	NA	5
T1W FS PG	Coronal	0.26	384 × 384	2.5/0.25	500	20	NA	5
T1W FS PG	Sagittal	0.278	576 × 576	2.5/0.25	500	20	NA	5

ETL, echo train length (ms); FS, fat saturation; Gap, gap between adjacent image slices (mm); NA, not applicable; PG, post-gadolinium; Pixel size, dimension of a square image pixel (mm); SE, spin-echo; SPAIR, spectral attenuated inversion recovery; ST, slice thickness (mm), STIR, short-tau inversion recovery; T1W, T1-weighted; T2W, T2-weighted; TE, echo time (ms); TI, inversion time (ms); TR, repetition time (ms).

Table 2.

Recommended magnetic resonance imaging (MRI) parameters for evaluation of subungual masses

Scanner properties:

• In general, imaging should be done with a high field-strength magnet. Although acceptable images can be created with a 1.5 T magnet, superior spatial resolution and decreased image noise are usually achieved with a 3.0 T magnet

Technique:

• The field of view should be centered over the subungual region • Use pixel dimensions as small as possible. With a surface coil and appropriate gradient coils, one may be able to achieve smaller pixel dimensions than the ones shown in Figure 3. Pixel dimensions may also be reduced if appropriate 3D imaging sequences are available and not too time intensive • Images can be optimized using smaller slice thickness and by reducing the gap (if possible) between adjacent slices. Patient positioning may inadvertently place the center of a small subungual mass in this gap. In such cases, it may be difficult or impossible to adequately visualize the mass. In such cases, reimaging the patient with a smaller pixel dimension and reduced gap can be helpful. The use of 3D imaging techniques can also be used to reduce this gap effectively to zero • The axial and sagittal planes are the most important planes for visualizing small subungual masses. If sequences must be curtailed to reduce total imaging time, the coronal sequences shown below could be omitted

See Table 3 for a sample MRI scanning protocol with parameters similar to those used in this study. These sample parameters can be used as a point of departure, as the exact parameters used will depend on the specific model of MRI machine in use at one’s facility.

Results

Eleven participants were recruited between the ages of 29–76 years old (64% female, mean age 52 +/− 15.5 years). Glomus tumor was clinically suspected or considered in 9 of 11 participants. For 4 of these 9 participants, imaging was instead consistent with myxoid cyst. Of the remaining 5 participants, imaging features were consistent with glomus tumors. 4 of these participants were found to have biopsy-supported glomus tumors; the 5th participant awaits biopsy.

Myxoid cyst was clinically suspected or considered in 7 of 11 participants, and imaging findings were supportive of the diagnosis in 6 participants. Of these 6 participants, 2 had biopsy results consistent with myxoid cyst, 2 more experienced spontaneous resolution of their mass consistent with clinical course of myxoid cyst, a 5th was confirmed via needle aspiration, and a 6th awaits biopsy.

Glomus Tumors

Of the 5 participants with imaging-suggested subungual glomus tumors (4 of which are biopsy-proven), 3 participants exhibited all three qualities of the classic triad. A fourth participant had history of pain and temperature sensitivity but an equivocal Love’s test. A fifth participant had pain and a positive Love’s test but no history of temperature sensitivity. The most involved digit was the thumb (n = 3) followed by the ring finger (n = 2).

On US, 100% of cases (5 of 5) demonstrated vascularity. Glomus tumors were additionally generally described as well-circumscribed, hypoechoic, and homogenous in US reports (shown in Fig. 1). All glomus tumors were avidly enhancing (post-gadolinium) and T2 hyperintense on MRI (note that one participant underwent CT in lieu of MRI, and their mass was avidly enhancing on CT). On MRI, 100% of impressions aligned with final histopathologic diagnosis of glomus tumor. Adjacent osseous cortical scalloping was present in 3 of 5 patients. For 2 of these patients, cortical scalloping was seen on MRI but no osseous change was seen on X-ray. Presence of vascularity agreed 100% of the time between US and MRI. Size measurements agreed between US and MRI with a Pearson correlation coefficient (r) of 0.91 (shown in Fig. 2).

Fig. 1.

Clinical and ultrasound images of a subungual glomus tumor. Ultrasound with doppler (on the right) demonstrates presence of vascular flow, which is a hallmark finding of glomus tumor on ultrasound. The image on the left shows the same glomus tumor on ultrasound without doppler.

Fig. 2.

Comparison of ultrasound and magnetic resonance imaging size measurements of subungual glomus tumors and myxoid cysts by volume. Size measurements by volume were compared between MRI and ultrasound, which are both well-established and non-disputed to provide accurate size estimates. Pearson linear coefficient (r = 1) of 0.91, indicative of near-linear correlation.

Myxoid Cysts

In 3 of 6 imaging-supported diagnoses of myxoid cysts, history of pain was present. One of 6 presented with history of temperature sensitivity. Of the 5 participants that underwent US, all demonstrated avascularity and presence of hypoechoic/anechoic quality (shown in Fig. 3). On MRI, 100% of final impressions aligned with final diagnosis, which was confirmed via biopsy, needle aspiration, or clinical course (spontaneous resolution). All diagnosed myxoid cysts showed T2 hyperintensity and absence of enhancement post administration of gadolinium on MRI. In 2 patients, there was underlying distal interphalangeal joint (DIP) osteoarthritis in the digit of myxoid cyst involvement on MRI. One of these patients did not undergo X-ray, and no osseous irregularity was seen on X-ray in the other. The absence of vascularity agreed between MRI and US. Lastly, size measurements agreed between US and MRI with a Pearson correlation coefficient (r) of 0.91 (shown in Fig. 2).

Fig. 3.

Subungual myxoid cyst preoperative, intraoperative, and ultrasound images. Characteristic extrusion of gelatinous-like fluid is seen intraoperatively. On ultrasound, typical hypoechoic, well-demarcated, and avascular qualities are demonstrated.

Discussion

In our short series, all lesions in every case were seen on both US and MRI, and diagnosis of subungual myxoid cysts and subungual glomus tumors was congruent between the two modalities. This supports the reliability of US in identifying key features of these lesions, with presence or absence of vascularity being a major feature used to differentiate myxoid cyst from glomus tumor. Using linear regression, size measurements agreed between US and MRI, confirming the well-established principle that US provides accurate size estimations for interventional or surgical planning. In regard to X-ray, MRI was more sensitive than X-ray in picking up cortical scalloping (glomus tumors) and osteoarthritis changes (myxoid cysts) when present.

Next, our study newly demonstrates that subungual glomus tumors and subungual myxoid cysts can be diagnostically imaged by a standard MRI machine when using an optimized protocol (shown in Table 3) and notably without the use of special equipment or coils [6, 7]. This opens evaluation to most radiology departments, thereby increasing accessibility and availability.

It is key to recognize that optimal diagnostic imaging of the subungual space is produced via customization of imaging protocols through collaboration with radiologists. Additionally, as stated in the literature [3] and informed by our radiologist, US technique can be user-dependent, and some sonographers may not have significant experience imaging subungual spaces. Awareness of this limitation is important and quality imaging therefore benefits from a sonographer who is familiar with the nail apparatus.

We recommend including the joint adjacent to the lesion in imaging field of view to evaluate joint involvement. The location of the lesion with respect to the nail fold should also be reported. When imaging the distal interphalangeal joint and nail fold, views should also include the nail bed and the hyponychium.

In summary, we see that US is congruent in diagnosis and size estimation when compared to MRI, that diagnostic MRI can be performed on standard MRI machines without the use of special equipment, and that collaboration with radiologists optimizes diagnostic imaging. As more data are accrued, future areas of interest include assessing non-inferiority of US when compared to MRI and assessing accuracy of US in involvement of surrounding tissues to assist surgical approach. All in all, the blending of both clinical and technical elements across dermatology and radiology has the potential to expand access to quality specialty care and expedite diagnosis of the nail apparatus pathology when imaging is needed.

Statement of Ethics

This study was approved by the University of Washington Institutional Review Board (IRB) Committee, FWA number 00006878. The University of Washington Institutional Review Board waived consent for study participation and inclusion of images for patients with lesions of the nail unit.

Conflict of Interest Statement

The authors have no conflict of interest to declare. Preliminary findings were reported as an abstract at the Society for Investigative Dermatology 2021 annual meeting (J Invest Dermatol 141 Suppl 1, S79, 2021). The authors report no additional disclosures in relation to this manuscript.

Funding Sources

There are no sponsors or funding pertaining to this research.

Author Contributor Statement

Alysha Dhami, MD: data analysis, writing – original draft, and writing – review and editing. S. Max Vale, MD: data analysis and writing – review and editing. Michael L. Richardson, MD: conceptualization, investigation, data analysis, writing – original draft, writing – review and editing, and supervision. April K. Schachtel, MD: data collection, writing – review and editing, and supervision. Philip Fleckman, MD: conceptualization, data collection, writing – review and editing, and supervision.

Funding Statement

There are no sponsors or funding pertaining to this research.

Data Availability Statement

All data generated or analyzed during this study are included in the manuscript. Further inquiries can be directed to the corresponding author.