Malignant proliferating trichilemmal tumor (MPTT) is an infrequent malignant neoplasm originating from cutaneous appendages, with only a handful of documented cases. This report delineates a unique instance of MPTT situated in the neck, accompanied by lymph node metastasis. A comprehensive exposition of its clinical trajectory and imaging manifestation is presented, aiming to enhance comprehension and management of this atypical ailment.

Patient concerns: A 79-year-old male presented with a longstanding right neck mass persisting for over six decades, exhibiting recent enlargement over the past year. Diagnoses: Enhanced magnetic resonance imaging of the neck unveiled an elliptical mass on the right neck side, characterized by an ill-defined border and a heterogeneous signal pattern. The mass exhibited subdued signal intensity on T1-weighted imaging (T1WI) and a heterogeneous high signal on T2-weighted imaging (T2WI), interspersed with a lengthy T1 and T2 cystic signal motif. Close anatomical association with the submandibular gland joint was noted, and intravenous gadolinium diethylene triamine pentaacetic acid administration facilitated conspicuous enhancement. Substantial enhancement of the solid segment prompted an initial preoperative diagnosis of malignant nerve sheath tumor. However, post-surgery histopathological and immunohistochemical analysis conclusively confirmed the diagnosis as malignant hyperplastic external hair root sheath tumor. Intervention: Complete excision of the tumor was successfully executed. Outcomes: The patient experienced a favorable postoperative recovery.

Malignant proliferative trichilemmal tumor external hair root sheath tumor is a cystic-solid lesion, appearing as low signal on T1WI images or high signal on T2WI with enhancement of the solid component. Suspicions of malignancy are heightened when the tumor border is indistinct, tissue planes are breached, or when linear or patchy high signals are observed in the subcutaneous tissue on T1 liver acquisition with volume acceleration enhanced images along with intermediate signal on T2WI and restricted diffusion on diffusion-weighted imaging images. Strong consideration for malignancy should arise if there are signs of compromised adjacent tissue relationships or direct invasion evident on imaging. We have incorporated the above-mentioned content into the entire manuscript.

Proliferating trichilemmal tumor (PTT) is an uncommon neoplasm originating from the outer hair sheath of the follicular isthmus within the dermis. It is characterized by well-defined borders, squamous cell attributes, and hyperkeratosis of the hair sheath[1]. The etiology of PTT remains enigmatic, although potential risk factors include infection, trauma, and exposure to ultraviolet light. The inaugural documented instance of PTT dates back to Jones’ report in 1966[2]. PTT predominantly emerges in sun-exposed regions of the body, with the head’s skin being the most frequent site[1,3]. Epidemiologically, this condition predominantly affects middle-aged and older women[4].

PTT represents a generally benign neoplasm with rare proclivity toward malignancy. In 1983, Saida et al[5] documented the initial case of malignant PTT (MPTT)[6]. Distorted mitosis, cytological diversity, peripheral infiltration, and aneuploidy have been observed across various cases[7]. PTT itself is a rarity, and the occurrence of MPTT accompanied by lymph node metastasis is exceedingly infrequent[8]. This article presents an exhaustive scrutiny of the clinical manifestation, imaging attributes, and surgical intervention strategy concerning a patient exhibiting typical clinical characteristics of malignant proliferative ependymoma in the neck, featuring lymph node metastasis.

Our final diagnosis of this case was MPTT, and the results were confirmed pathologically, as shown in Figure 2.

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Figure 2 Pathological findings. A: Vigorous tumor growth [hepatic encephalopathy (HE) × 100)]; B: Lymph node metastasis; C: Tumor nests (HE × 50).

Complete excision of the tumor was successfully executed.

The patient experienced a favorable postoperative recovery.

PTT is a rare cutaneous tumor, with research indicating that 80% of affected individuals are women over the age of 60[3]. Predominantly, 90% of these tumors manifest on the scalp, followed by occurrences on the forehead and neck skin[9]. Moreover, most instances of MPTT are conceived as localized malignancies evolving from pre-existing PTT lesions[10]. It is noteworthy that there exist limited reports of PTT undergoing malignant transformation on the scalp. Thus far, occurrences of MPTT with lymph node metastases within the neck’s skin are isolated and scarce. The radiographic representation of PTT/MPTT harmonizes with its clinical manifestation. Lesions on the head and neck typically exhibit characteristics of cystic-solid or cystic masses[10]. Appearing as low signal on T1WI images or high signal on T2WI with enhancement of the solid component. Suspicions of malignancy are heightened when the tumor border is indistinct, tissue planes are breached, or when linear or patchy high signals are observed in the subcutaneous tissue on T1 liver acquisition with volume acceleration enhanced images along with intermediate signal on T2WI and restricted diffusion on diffusion-weighted imaging images. Strong consideration for malignancy should arise if there are signs of compromised adjacent tissue relationships or direct invasion evident on imaging[11].

Proliferative ectodermal root sheath tumors are categorized into three groups: Group I (benign), marked by restricted lesions, mild nuclear heterogeneity, lack of mitotic activity, and absence of necrosis or lymphovascular infiltration; group II (low malignancy), characterized by histological irregularity, localized infiltration, and potential spread to dermal and subcutaneous tissues; and group III (highly malignant), characterized by infiltrative growth, pronounced nuclear heterogeneity, elevated mitotic and necrotic activity, and lymphatic and vascular infiltration[10,12]. Histologically, PTT masses typically display lobulated, well-defined contours without encapsulation. The tumor cells frequently resemble acanthocytes, forming irregular nests or cords, often exhibiting marked central keratinization. Small cystic or glandular lacunae containing keratinized material can be observed, resembling hair follicle differentiation. Nuclei present mild heterogeneity, occasionally with clusters of cells embedded in the mesenchyme and even beads of keratinization, a feature that can lead to confusion with squamous cell carcinoma. In contrast, MPTT tends to occupy deeper layers, mainly within the dermis or subcutaneous tissue. It displays infiltrative growth, notable nuclear heterogeneity, prominent atypical mitosis, and lymph node metastasis[13,14]. While no specific immunohistochemical markers exist for MPTT diagnosis, immunohistochemical studies continue to aid in distinguishing PTT from MPTT. In recent times, markers like p53 and Ki-67 have garnered attention, with certain studies revealing elevated expression of Ki-67 and p53 staining in MPTT. Concerning its biological behavior, PTT, especially MPTT, holds the potential for recurrence and metastasis, giving rise to local lymph node metastases or even distant systemic spread[9].

The tumor was situated within the right medial sternocleidomastoid muscle, exhibiting local infiltration, aberrant nuclear division, and lymphatic and vascular infiltration, categorically aligning with the highly malignant PTT category. In the context of the neck tumor, differentiation from lymphoma and malignant nerve sheath tumor is imperative. The primary intervention for MPTT entails surgical resection, necessitating extensive local excision of the tumor alongside approximately 1 cm of surrounding normal tissue to achieve a secure margin[4]. A stringent postoperative follow-up regimen is advisable for MPTT cases. Radiotherapy and chemotherapy have been applied for recurrent MPTT cases; however, given the rarity of this malignancy, published cases are insufficient for a comprehensive assessment of the efficacy and safety of these interventions. In summation, surgical excision remains the principal approach for MPTT management, with long-term monitoring imperative. Alternative therapeutic modalities warrant further comprehensive evaluation.

In summary, this case highlights the rarity and complexity of highly MPTT. Despite its infrequent occurrence, MPTT can lead to lymph node metastases in the neck’s skin. Radiographic and histological features correspond with clinical presentation, aiding diagnosis. Surgical resection remains the mainstay of treatment, while the efficacy of alternative therapies needs further exploration. Long-term follow-up is essential, emphasizing the need for continued research in MPTT management.