A Case of a Giant Trichilemmal Cyst on the Forehead

Abstract

Trichilemmal cysts are the most common benign subcutaneous cysts on the scalp. Approximately 90% of trichilemmal cysts appear on the scalp and have trichilemmal keratinization without a granular layer visible on pathological examination. In addition, proliferating trichilemmal tumors, which occur in 2% of trichilemmal cysts, show local recurrence and ulceration, making them highly locally aggressive and requiring careful differentiation. We report the case of a 56-year-old man with a giant trichilemmal cyst on his forehead. After computed tomography and magnetic resonance imaging, a subcutaneous cyst was suspected and excised, and a pathological diagnosis of trichilemmal cyst was established. This was a rare case as the trichilemmal cyst was not located on the scalp, the most common site, but on the forehead area, and it was exceedingly large, with a maximum diameter of 9 cm.

Background

Trichilemmal cysts (TCs) are the most common benign subcutaneous cysts on the scalp, with approximately 90% of them occurring on the scalp and presenting with trichilemmal keratinization without a granular layer on pathological examination. By contrast, epidermoid cysts (ECs), which are the most common type of subcutaneous cysts, are characterized by a granular layer of skin similar to normal skin. In addition, proliferating trichilemmal tumors (PTTs), which occur in 2% of TCs, show local recurrence and ulceration, making them highly aggressive locally and requiring careful differentiation. We report the case of a 56-year-old man with a gigantic TC in the forehead area.

Case Report

A 56-year-old man was aware of a mass in the left frontal region for approximately 5 years, which gradually increased in size and caused visual field disturbance. The patient was referred to our department for further examination and treatment. His past medical and family histories were unremarkable. At the time of his initial visit, a mass measuring 9 cm in its greatest dimension and 6 cm in stem diameter was observed in the left anterior part of his forehead (Figure 1). The mass' elasticity was soft, and there was no tenderness. Computed tomography (CT) imaging revealed homogeneous internal findings with some calcification (Figure 2a) and no osteolysis in the adjacent skull (Figure 2b). On magnetic resonance imaging (MRI), T1-weighted images showed an internal iso- to high signal when compared to the gray matter (Figure 3a), T2-weighted images showed an internal uniformly high signal (Figure 3b), and contrast-enhanced T1-weighted images showed a slightly high internal signal with no contrast effect (Figure 3c). A subcutaneous cyst was suspected, and a decision was made to perform resection.

Figure 1.

Tumor photograph. A spherical tumor 9 cm in diameter in the left anterior forehead area hanging over the visual field.

Figure 2.

CT image of the tumor. (a) A calcified lesion is visible in the tumor. (b) The skull area directly below the tumor is intact.

Figure 3.

MRI images of the tumor. (a) T1-weighted image shows an equal to slightly higher signal inside the tumor compared to the gray matter. (b) T2-weighted image shows a high signal inside the tumor. (c) Contrast-enhanced T1-weighted image shows no contrast effect inside the tumor.

Under general anesthesia, the patient was placed in the supine position. The skin incision line was designed in a transverse spindle shape, and a part of the skin at the tumor stem was retained for suturing (Figure 4a). The base of the tumor was in contact with the frontalis muscle, and the tumor was dissected over the muscle and excised. The supraorbital nerve, which was displaced by the tumor, was identified and preserved (Figure 4b). A 5-0 absorbable thread was used for dermal sutures and a 5-0 nylon thread for skin sutures (Figure 4c). The resected tumor had a diameter of 9 cm, and its entire capsule was removed (Figure 5).

Figure 4.

Photographs of the surgery. (a) The skin incision is designed to ensure suturing. (b) The supraorbital nerve is shown, compressed by the tumor. (c) Skin after suturing.

Figure 5.

Photograph of the resected tumor. Its diameter is 9 cm, and the entire capsule is removed.

Pathological findings showed that the tumor was a monolocular cyst with unstructured contents and some calcifications. The inner wall was a multilayered squamous epithelium with a single basal layer and keratinization, without a granular cell layer (Figure 6a). Some papillary structures were observed, but there was no hyperplasia of cellular components or any cellular atypia (Figure 6b). On the basis of the above findings, a diagnosis of TC was made. Two years postoperatively, the patient had no recurrence of TC, and there was no sensory disturbance in the surrounding area (Figure 7).

Figure 6.

Micrographs. (a) Keratinization is seen without a granular layer (trichilemmal keratinization). (b) Papillary structure. No cell proliferation can be observed.

Figure 7.

Photograph taken 2 years after surgery. The sutures are progressing well, and there is no recurrence.

Discussion

TC occurs on the scalp in 90% of cases and accounts for approximately 40% of all masses on the scalp. It is the most common subcutaneous cyst on the scalp, mostly found in middle-aged women^1,2). In a report of 54 TC cases, the mean age was 43.4 years (range, 15-80), 44% were male and 56% were female (relatively more common in females), and the sites were the scalp (68%), extremities (15%), neck (9%), trunk (4%), postauricular region (2%), and scrotum (2%). If the lesion is not inflamed, it does not cause pain or other symptoms³⁾. Treatment is by simple excision, and total excision including the capsule is recommended⁴⁾.

Pathologically, the inner wall of an EC has basal and spinous cell layers, as does normal skin. Keratinization occurs through the granular cell layer, whereas the inner wall of TCs shows trichilemmal keratinization without the granular cell layer^1,5,6). The contents of ECs are layers of keratin, whereas TCs are densely packed with unstructured acidophilic keratin, and cholesterol fissures as well as calcifications are often present⁵⁾. Calcification reportedly occurs in 65%-75% of TCs⁷⁾, and some was observed in the present case. It has also been reported that calcification is more likely to be seen in TCs on the scalp than in TCs on other parts of the body³⁾.

The thin capsule of ECs tends to rupture or become infected, but the tough capsule of TCs tends to prevent these issues. The entire capsule can be easily removed during resection without rupture⁵⁾. The TC in the present case also had a relatively strong capsule that was completely removed.

In a literature review of 185 PTT cases, 80.0% of the tumors were located on the scalp and the site of origin tended to be similar to that of TCs⁸⁾. The pathological findings of PTT can be distinguished from those of TC by the presence of an increased cellular component directed toward the lumen⁶⁾. Most TCs are monoblastic, whereas most PTTs form multiblastic masses⁹⁾. Although malignant tumors with cellular dysplasia were previously classified as malignant PTTs, the 2018 4th edition of the WHO classification defines PTT as a disease concept that includes the same spectrum from benign to malignant; although recurrence and ulceration may be seen, metastases are rare⁶⁾.

Several studies have described the imaging features of TC and PTT. On CT images, low-density areas reflecting keratin and calcification are frequently observed in both TCs and PTTs¹⁰⁾. On MRI, TC T1-weighted images show an iso- to high signal in the mass interior when compared to gray matter, whereas PTTs show a low signal. This difference is thought to be due to the abundant presence of dense keratin and calcified lesions within the TC cyst, whereas the proportion of these lesions is relatively small in PTT because of the marked increase in cellular components in the lumen⁹⁾. On contrast-enhanced MRI images, TC shows a contrast effect only on the capsule, whereas PTT shows a heterogeneous signal due to the mixture of contrast-enhancing cellular components and non-contrast-enhancing necrotic areas and contents^10,11).

The present patient presented with a monoblastic and keratin-enriched lesion, and although a papillary-like structure was seen in a part of the inner wall, there was no cellular proliferation. Thus, a diagnosis of TC was made. Preoperative imaging was also consistent with TC as CT images showed characteristic internal calcification and no osteolysis. MRI images showed an iso- to high signal when compared to gray matter on T1-weighted images and contrast-enhanced T1-weighted images with a contrast effect on the capsule only, which was also consistent with TC.

Although there are no comprehensive epidemiological data on tumor size, there have been few reports of TCs as large as that in the present case. In two previous reports of giant TCs, the diameter increased to 70 mm in 4 years and 60 mm in 30 years^12,13). Although there are many reports of cases of rapid enlargement in PTTs, the enlargement of a TC to 90 mm in diameter within 5 years, as in the present case, is considered relatively rapid and unusual. The location of the tumor was not on the scalp, which is its common site, but on the forehead, making this a rare case. Preoperative imaging should be performed after careful consideration of the possibility of PTT recurrence or ulceration, and careful follow-up is recommended, especially in the case of PTT.

Author Contributions: N.T. and K.A. designed the study; K.A., Y.Y., and Y.T. performed the experiment; and N.T. wrote the manuscript.

Conflicts of Interest: There are no conflicts of interest.

Consent to Participate: The patient provided written informed consent to participate in this study.

Consent for Publication: Written informed consent for the publication of the images and information about the patient was obtained.