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Skin nonmelanocytic tumor

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Follicular derived

Fibrofolliculoma / trichodiscoma


Azadeh Samiei, M.D.
Shira Ronen, M.D.

Last author update: 10 February 2025
Last staff update: 10 February 2025

Copyright: 2002-2025, PathologyOutlines.com, Inc.

PubMed Search: Fibrofolliculoma / trichodiscoma

Azadeh Samiei, M.D.
Shira Ronen, M.D.
Page views in 2025 to date: 3,129
Table of Contents
Definition / general | Essential features | Terminology | ICD coding | Epidemiology | Sites | Pathophysiology | Etiology | Clinical features | Diagnosis | Prognostic factors | Case reports | Treatment | Clinical images | Microscopic (histologic) description | Microscopic (histologic) images | Positive stains | Negative stains | Molecular / cytogenetics description | Videos | Sample pathology report | Differential diagnosis | Additional references | Board review style question #1 | Board review style answer #1 | Board review style question #2 | Board review style answer #2
Cite this page: Samiei A, Ronen S. Fibrofolliculoma / trichodiscoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skintumornonmelanocyticfolliculofibroma.html. Accessed March 30th, 2025.
Definition / general
  • Benign hamartomatous proliferations with both follicular epithelial and mesenchymal differentiation
  • Multiple lesions are a cutaneous manifestation and hallmark of Birt-Hogg-Dubé syndrome and less commonly familial multiple trichodiscoma syndrome and tuberous sclerosis syndrome
Essential features
  • Infundibulocentric hamartomatous proliferation of follicular unit with 2 components: undifferentiated cords of epithelium originating from the hair mantle and the surrounding stroma
  • Solitary or multiple firm, white to skin colored papules presenting on head and neck and upper trunk, especially on the nose and perinasal areas
  • Multiple lesions are a key dermatologic feature of Birt-Hogg-Dubé syndrome (multiple fibrofolliculomas, trichodiscomas, acrochordons, angiofibromas, oral papules, cutaneous collagenomas, renal neoplasms and pulmonary cysts)
  • Fibrofolliculoma, trichodiscoma and spindle cell predominant trichodiscoma are morphological variants within a related spectrum of lesions
Terminology
ICD coding
  • ICD-O: 8391/0 - fibrofolliculoma / trichodiscoma
  • ICD-11: 2F22 & XH4YU8 - benign neoplasms of epidermal appendages & follicular fibroma
Epidemiology
Sites
Pathophysiology
  • Exact pathophysiology has not been established; however, these lesions appear to arise from the stem cells of the hair mantle, resulting in a hamartomatous proliferation (J Cutan Pathol 2002;29:529)
  • In Birt-Hogg-Dubé syndrome, a germline mutation in the folliculin gene (FLCN, chromosome 17p11.2) leads to the development of multiple lesions early in life (Cancer Cell 2002;2:157, Am J Hum Genet 2005;76:1023)
Etiology
  • Etiology of sporadic lesions is unclear
  • In Birt-Hogg-Dubé syndrome (an inherited autosomal dominant condition), pathogenic variants in the folliculin (FLCN) gene contribute to the development of these lesions (Nat Rev Urol 2015;12:558)
Clinical features
Diagnosis
Prognostic factors
  • Skin lesions are completely benign and have a good prognosis
  • In Birt-Hogg-Dubé syndrome, prognosis is reliant on noncutaneous manifestations, such as renal cell carcinoma
Case reports
Treatment
Clinical images

Contributed by Azadeh Samiei, M.D.
Skin colored papules

Skin colored papules



Images hosted on other servers:
Numerous skin colored to white papules

Numerous skin colored to white papules

Multiple isolated and coalescing papules

Multiple isolated and coalescing papules

Microscopic (histologic) description
  • Fibrofolliculoma / trichodiscoma
    • Usually round, symmetric, well circumscribed nodule composed of a central dilated follicle and surrounding stroma
    • Thin, elongated strands of follicular epithelium emanate from the infundibulum
    • Epithelial strands may exhibit several attachments to both the follicle and surface epithelium
    • Characteristic surrounding stroma is composed of fibrillary ribbon-like collagen, mucin and fibrocytes in varying proportion
    • Collagen bundles are often arranged parallel to each other and somewhat perpendicular to the epithelial cell strands
    • Hair follicles may have an irregularly dilated central lumen filled with keratin
    • Trichodiscoma is believed to be on the same spectrum as an evolving fibrofolliculoma, characterized by a predominance of stromal elements, with peripheral clusters of sebaceous lobules described as mitts or hands of banana (radiating outward, resembling the fingers of a mitten or shape of a banana)
    • No histopathologic differences exist between syndrome associated cases of fibrofolliculoma / trichodiscoma and sporadic ones
  • Diverse morphological variants described (Am J Dermatopathol 2014;36:734)
    • Spindle cell predominant trichodiscoma: a variant with abundant mucinous stroma and acellular haphazard proliferation of fibrocytes; the individual stromal cells have elongated, slightly wavy nuclei and delicate tapering cytoplasm
    • Myxoid / mucin predominant
    • Stromal lipomatous metaplasia
    • Pseudocartilaginous, sclerotic / fibrotic
    • Cases with prominent vasculature or entrapment of adnexal structures such as apocrine or eccrine duct have been reported
Microscopic (histologic) images

Contributed by Azadeh Samiei, M.D.
Spindle cell predominant trichodiscoma

Spindle cell predominant trichodiscoma

Stromal spindle cells

Stromal spindle cells

Sclerotic

Sclerotic


Sclerotic

Sclerotic

Dilated follicle

Dilated follicle

Cystically dilated follicle

Cystically dilated follicle


Shrinking follicle

Shrinking follicle

Anastomosing epithelial strands

Anastomosing epithelial strands

Anastomosing epithelial strands

CD34

Positive stains
Negative stains
  • S100 (positive only in nerves entrapped among stromal spindle cells; spindle cell predominant trichodiscoma was previously thought to be a neurofollicular hamartoma with neural origin of spindle cells) (Am J Dermatopathol 2006;28:1)
Molecular / cytogenetics description
  • In patients with multiple skin lesions, a genetic consultation for Birt-Hogg-Dubé syndrome is necessary
  • Testing for Birt-Hogg-Dubé syndrome includes FLCN gene mutation analysis to identify pathogenic variants
  • Based on the spectrum of clinical findings, genetic testing may include (Nat Rev Urol 2015;12:558)
    • Single gene testing
      • Targeted analysis of FLCN gene for small intragenic deletions / insertions, missense, nonsense and splice site variants
      • If no variants are detected, gene targeted deletion / duplication analysis is performed to detect exon and whole gene deletions or duplications
    • Multigene panel
      • Includes testing for FLCN gene mutations among a group of selected genes
      • May include custom panels based on clinician specifications
      • Should incorporate deletion / duplication analysis alongside sequence testing
Videos

 

Fibrofolliculoma

Sample pathology report
  • Skin, cheek, biopsy:
    • Fibrofolliculoma (see comment)
    • Comment: Histologic sections demonstrate an infundibulocentric proliferation with central dilated infundibulum, from which delicate anastomosing epithelial strands and cords of basaloid cells emanate, producing a fenestrated pattern and encasing a characteristic stroma composed of fibrillary collagen, mucin and fibroblasts in varying proportions. These histologic findings are those of fibrofolliculoma. Given the presence of multiple indurated nodules, it is important to consider Birt-Hogg-Dubé syndrome in this clinical context. Further evaluation is warranted to explore potential underlying conditions.
Differential diagnosis
  • Angiofibroma / fibrous papule:
    • Solitary lesions on the nose or central face
    • Superficially situated dermal lesion with thin walled ectatic blood vessels within a dense collagenous stroma
    • Stromal fibroblasts are typically bland but may occasionally be multinucleated
  • Tumor of follicular infundibulum:
    • Cords and sheaths of epithelium growing parallel to the overlying epidermis
    • Lesions exhibit multiple connections to adjacent follicular structure and the overlying epidermis
    • Cells are bland, resembling a benign squamous proliferation, featuring enlarged eosinophilic squamous cells, along with smaller basaloid cells and palisading at the periphery
  • Trichofolliculoma:
    • Folliculocystic tumor characterized by a central cystic space that opens to the skin surface, surrounded by acanthotic keratinizing follicular epithelium (the parent follicle)
    • Central cyst is filled with keratin debris and hair shafts
    • Numerous smaller follicles radiate from the parent follicle
    • There may be attached sebaceous glands
  • Inverted follicular keratosis:
    • Well circumscribed, symmetric endophytic and occasionally exoendophytic proliferation arising from the follicular infundibulum
    • Characteristic feature is the presence of numerous squamous eddies
    • Overlying epidermis may show central erosion, hyperkeratosis and parakeratosis
  • Neurofibroma:
    • Relatively circumscribed lesion within the dermis
    • Lesion consists of loosely arranged bland spindle cells within a myxoid to collagenous stroma
    • Intralesional mast cells are commonly present
    • Lesional cells show positivity for S100, SOX10 and CD34 (a characteristic fingerprint pattern)
  • Basal cell carcinoma (BCC):
    • Nests of immature basaloid cells with peripheral palisading
    • Mucin deposition and artifactual retraction of stroma around nests
    • IHC staining is not required; however, BCC is usually strongly positive for BerEP4, MOC31 and BCL2
  • Dermatofibroma:
    • Dermal based proliferation that may extend deep into the dermis
    • More cellular lesion with fibrohistiocytic proliferation and peripheral collagen entrapment
    • Overlying epithelium may show basilar or sebaceous induction
    • Lesion is usually separated from the overlying epidermis with a Grenz zone
    • Fibrohistiocytes may be weakly positive for factor XIIIa or CD68
    • Lesional cells are negative for CD34 (periphery of the lesion may show staining with CD34)
  • Spindle cell lipoma:
    • Dermal or intramuscular tumor composed of mature adipocytes, bland spindle cells and ropey collagen
    • Spindle cells are bland with uniform nuclei and arranged either in short fascicles resembling the "school of fish" pattern or in a more random distribution
    • Positive for CD34 with loss of nuclear RB1 protein staining
Board review style question #1


A 32 year old patient presents with multiple asymptomatic skin papules on the face and neck. Histopathological examination reveals a dome shaped papule with infundibulocentric proliferation of delicate epithelial strands and surrounding stroma. What is the most likely diagnosis?

  1. Basal cell carcinoma
  2. Dermatofibroma
  3. Fibrofolliculoma
  4. Trichofolliculoma
Board review style answer #1
C. Fibrofolliculomas mostly present on the face and neck, featuring thin strands of epithelial cells surrounded by a fibrous or fibromyxoid stroma. Answer A is incorrect because basal cell carcinoma is characterized by blue basaloid cells, peripheral palisading and artifactual clefting around nests. Answer B is incorrect because dermatofibroma is more cellular and composed of fibrohistiocytic cells, entrapping collagen at the periphery. Answer D is incorrect because trichofolliculoma displays a parent follicle with central cystic dilatation and numerous smaller radiating follicles.

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Reference: Fibrofolliculoma / trichodiscoma
Board review style question #2
A young patient with a history of multiple fibrofolliculomas and spontaneous pneumothorax is evaluated for underlying syndromes. Which of the following syndromes is most commonly associated with fibrofolliculomas?

  1. Birt-Hogg-Dubé syndrome
  2. Cowden syndrome
  3. Gardner syndrome
  4. Tuberous sclerosis
Board review style answer #2
A. Birt-Hogg-Dubé syndrome. Fibrofolliculomas are most commonly associated with Birt-Hogg-Dubé syndrome, a genetic disorder linked to mutations in the FLCN gene. This syndrome is characterized by the presence of multiple fibrofolliculomas, trichodiscomas, acrochordons and an increased risk of renal cell carcinoma. In general, the triad of skin papules, spontaneous pneumothorax and renal tumors in a young adult over 20 years of age should always raise the clinical suspicion of Brit-Hogg-Dubé syndrome. Answer B is incorrect because Cowden syndrome is associated with mutations in the PTEN gene and is characterized by multiple hamartomas, including trichilemmomas, rather than fibrofolliculomas. Answer C is incorrect because Gardner syndrome, linked to familial adenomatous polyposis (FAP), typically features multiple epidermoid / epidermal inclusion cysts, not fibrofolliculomas. Answer D is incorrect because although multiple fibrofolliculomas can be seen in tuberous sclerosis, this condition is more commonly associated with angiofibromas. Fibrofolliculomas, on the other hand, are primarily linked to Birt-Hogg-Dubé syndrome.

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Reference: Fibrofolliculoma / trichodiscoma
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