Sacral dimple: clinical perspectives of lesions hidden beneath the skin

Jin Eun; Kwan Sung Lee; Seung Ho Yang

doi:10.3345/cep.2025.01802

Clin Exp Pediatr > Volume 69(2); 2026

Eun, Lee, and Yang: Sacral dimple: clinical perspectives of lesions hidden beneath the skin

Review Article

Neurology

Sacral dimple: clinical perspectives of lesions hidden beneath the skin

Jin Eun, MD, PhD¹

, Kwan Sung Lee, MD, PhD²

, Seung Ho Yang, MD, PhD³

¹Department of Neurosurgery, Eunpyeong St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea

²Department of Neurosurgery, Seoul St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea

³Department of Neurosurgery, St. Vincent’s Hospital, College of Medicine, The Catholic University of Korea, Suwon, Korea

Corresponding author: Seung Ho Yang, MD, PhD. Department of Neurosurgery, St. Vincent’s Hospital, College of Medicine, The Catholic University of Korea, 93 Jungbudaero, Paldal-gu, Suwon 16247, Korea Email: 72ysh@catholic.ac.kr

Received August 8, 2025 Revised September 25, 2025 Accepted October 1, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Clinical and Experimental Pediatrics 2026;69(2):103-113.

Published online: November 26, 2025

DOI: https://doi.org/10.3345/cep.2025.01802

Abstract

Sacral dimples are the most common cutaneous anomalies in newborns. While usually benign anatomical variants, some dimples are indicative of occult spinal dysraphism, such as a tethered cord, dermal sinus tract, or lipomyelomeningocele, that, if undiagnosed, may cause irreversible neurological, orthopedic, and urological deficits. Distinguishing benign from high-risk dimples is essential for timely intervention. This review summarizes the embryological origins, diagnostic criteria, imaging approaches, and management strategies for sacral dimples to help clinicians identify cases requiring further evaluation. A comprehensive literature review examines the embryology of caudal spinal development, classification of spinal dysraphism, and studies of the diagnostic accuracy of ultrasonography and magnetic resonance imaging (MRI) in infants with sacral dimples. Guidelines and high-quality studies of the surgical outcomes of tethered cords and related anomalies were also analyzed. The literature search and study selection followed the Preferred Reporting Items for Systematic Reviews and Meta- Analyses flow. Simple sacral dimples—solitary midline depressions less than 5 mm in diameter, located within 2.5 cm of the anus, and lacking associated cutaneous stigmata—are not associated with spinal dysraphism and do not require imaging. In contrast, atypical dimples (large, deep, off-midline, or associated with skin markers such as hair tufts or hemangiomas) are significantly associated with occult anomalies and warrant imaging, beginning with spinal ultrasonography in neonates and MRI in older infants or equivocal cases. Conditions such as tethered cord, dermal sinus tract, lipomyelomeningocele, and split cord malformations are best visualized using MRI. Early surgical detethering improves neurological, orthopedic, and bladder outcomes, whereas delayed intervention risks permanent deficits. Applying standardized criteria and targeted imaging avoids unnecessary investigations while ensuring a timely diagnosis of occult spinal dysraphism. Early recognition and appropriate surgical management, when indicated, are critical for preventing neurological deterioration and improving the prognosis of affected infants.

Key words: Sacrum, Spinal cord, Neural tube defects, Tethered cord syndrome

Key message

· Most sacral dimples are benign, but atypical features may indicate occult spinal dysraphism.

· Simple dimples meeting strict criteria require no imaging, whereas atypical dimples require targeted ultrasonography or magnetic resonance imaging.

· The early diagnosis and surgical management of highrisk cases prevents irreversible neurological, orthopedic, and urological deficits.

Introduction

Cutaneous dimples, skin depressions that may be accompanied by pits or creases, are observed in healthy children and may be associated with various dysmorphic syndromes [1]. While often regarded as benign and of cosmetic significance, dimples can be the initial clinical indicator of an underlying developmental abnormality. These lesions are seen in a spectrum of conditions including congenital syndromes, skeletal disorders, infectious processes, inborn errors of metabolism, and mechanical trauma [1]. When a cutaneous dimple is identified, clinicians should conduct a thorough physical examination consisting of carefully assessing dimple number, location, and characteristics along with any dysmorphic features and neurological or orthopedic abnormalities.

Sacral dimples, also referred to as sacrococcygeal or coccygeal dimples or pits, are the most frequently encountered cutaneous anomalies during neonatal spinal assessments. These dimples present as shallow or deep depressions in the lower sacral region, typically within or near the natal cleft [1]. The prevalence of sacral dimples in newborns is approximately 1.8%–7.2% [2]. Most sacral dimples are benign, particularly those that are less than 0.5 cm in diameter, singular, and located at midline (Fig. 1). In contrast, dimples that are large, deep, located far from the anus, or associated with hair or exhibit discoloration may be indicative of underlying pathology [2]. A simple sacral dimple is defined as a solitary midline lesion less than 5 mm in diameter that is situated within 2.5 cm of the anus and unaccompanied by drainage or associated cutaneous stigmata such as hypertrichosis, hemangiomas, skin tags, or vestigial tails [3]. Importantly, a coccygeal pit is generally considered a normal anatomical variant without communication with intraspinal structures and does not necessitate further imaging (Fig. 2). However, a true sacral dimple may warrant additional evaluation, as it may be a cutaneous marker of occult spinal dysraphism, with tethered cord syndrome being the most clinically significant example. In the screening of sacral dimples, the reported incidence of abnormal underlying pathology is 0%–3.4% [4,5].

Methods

A systematic review of the literature was conducted to examine sacral dimples, with a particular emphasis on its clinical significance, associated pathologies, and imaging evaluation. The review process followed the general principles of systematic literature searches and reporting standards recommended by Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. A structured search was conducted of PubMed using the keyword “sacral dimple.” Titles and abstracts were screened to identify potentially relevant articles. Fulltext assessments were performed to determine eligibility according to predefined inclusion and exclusion criteria. Case reports, technical notes, and non-English articles were excluded from the final analysis. The selection process was summarized in a PRISMA flow diagram (Fig. 3). In addition to reviewing the general epidemiology and clinical presentations, we extracted and organized information in specific categories relevant to clinical practice and research: pathophysiology, diagnosis, imaging and treatment. Each domain was reviewed to highlight current evidence, controversies, and knowledge gaps.

Results

The initial PubMed search retrieved 96 records. The title and abstract screening eliminated 52 articles. Among the remaining 44 records, the full text for 2 could not be retrieved. Thus, a total of 42 reports underwent fulltext assessment. Of these, 24 case reports, 2 professional reports, and one non-English article were excluded. Ultimately, 15 studies met the eligibility criteria and were included in the qualitative synthesis. Among the 15 included articles, 10 were retrospective, 3 were physician surveys, and 2 were reviews.

1. Pathophysiology

1) Normal development of caudal neural tube

The formation of the neural tube, a critical early event in the development of the central nervous system, occurs through the process of neurulation, which begins around gestational days 18–28. During this period, the ectoderm overlying the notochord proliferates to form the neural plate, which subsequently folds to become the neural folds and eventually fuses into the neural tube. Concurrently, the paramedian somites differentiate into sclerotome cells, contributing to the development of vertebral structures [6,7].

Closure of the neural tube initiates at days 22–23, starting at the prospective cervical level and progressing in the cranial and caudal directions. The final closure point is the posterior neuropore, which seals by gestational days 26–27. However, neurulation alone does not complete the neural tube formation. The most caudal portion of the tube forms through a distinct process known as canalization that occurs between gestational days 28 and 48 [7,8].

Beneath the posterior neuropore, undifferentiated cells from the primitive streak aggregate to form the caudal cell mass. Between days 28 and 42, this mass undergoes vacuolization and the resulting vacuoles coalesce to establish the distal neural tube. These structures give rise to the conus medullaris, cauda equina, and filum terminale. Between days 43 and 48, the ventriculus terminalis, a transient cystic cavity near the terminus of the caudal neural tube, develops; it is initially located at the coccygeal level, marking the future site of the conus medullaris [6].

As gestation progresses, the terminal spinal cord undergoes retrogressive differentiation, leading to the elongation of the filum terminale, development of the cauda equina, and apparent ascension of the conus medullaris relative to the vertebral column. The portion of the neural tube distal to the ventriculus terminalis regresses to become the fibrous filum terminale, extending from the conus to the coccygeal medullary vestige, an epidermal remnant at the coccygeal level.

The conus ascent occurs as a result of disproportionate growth of the vertebral column versus spinal cord. Consequently, the spinal nerve roots elongate to maintain their connections to the corresponding vertebral foramina, resulting in the characteristic fan-like structure of the cauda equina. This maturation process continues into the postnatal period; by approximately gestational day 60, the conus medullaris reaches its adult position, typically at the L1–2 intervertebral level [9,10].

2) Abnormal development and spinal dysraphism

Spinal dysraphism refers to a spectrum of congenital anomalies resulting from incomplete or aberrant neural tube formation and closure. These defects are broadly classified into open (aperta) and closed (occult) types, reflecting neural element exposure degree (Table 1) [9].

3) Open spinal dysraphism

Open spinal dysraphism arises from the failure of primary neurulation, leading to incomplete closure of the neural tube and overlying structure. In spinal bifida aperta, the dura and posterior vertebral arches fail to fuse and the normal skin and subcutaneous tissue do not develop, resulting in direct exposure of the neural elements. The exposed spinal tissue, continuous with the surrounding skin via a thin epithelialized layer (zone epithelioma), remains tethered and low-lying as a result of the disrupted retrogressive differentiation. Myelomeningocele is a severe form of open dysraphism in which the spinal cord and meninges herniate through the defect. A meningocele involves herniation of the cerebrospinal fluid and meninges only, whereas the neural tissue remains intact but is displaced. Myeloschisis represents the most extreme failure, in which open and unfused neural tissue is directly exposed without any membranous covering, a condition incompatible with long-term survival. A split cord malformation with myelomeningocele (hemimyelomeningocele) combines features of duplicated cords with those of open neural tube defects [11,12].

4) Closed spinal dysraphism

Closed spinal dysraphism results from disturbances in secondary neurulation, canalization, or disjunction and is characterized by an intact tissue cover overlying the spinal defect. Although the neural tube closes, anomalies such as lipomas, fibrous bands, or sinus tracts can lead to tethered cord syndrome and associated neurological deficits. Thickened filum terminale and fatty filum are thought to result from incomplete regression during secondary neurulation. Dermal sinus tracts arise from incomplete separation between the surface and neural ectoderm that results in epithelial-lined channels that may extend to the intrathecal structures, thereby serving as a conduit for infection (e.g., meningitis) and forming dermoid or epidermoid tumors that may tether the cord. Lumbosacral lipomas and lipomyelomeningocele originate from abnormal differentiation of mesodermal tissue within the caudal cell mass. These fatty masses may herniate through bony defects, thereby tethering the conus or causing compression. A split cord malformation (diastematomyelia) occurs due to persistence of the neurenteric canal, leading to the formation of dural hemicords separated by a fibrous, cartilaginous, or bony septum. Affected patients may present with low-lying conus, scoliosis, and other associated anomalies. Neurenteric cysts, which result from incomplete separation of the notochord and endoderm, can similarly compress or tether the spinal cord [13,14].

Diagnosis

A detailed physical examination is performed to evaluate key morphological features of a dimple. Important characteristics include its exact location—whether it lies within the gluteal cleft or in a higher paraspinal position—depth (shallow versus deep), and number of lesions (solitary or multiple). Of particular clinical relevance is the presence of cutaneous stigmata such as localized hypertrichosis, vascular malformations (e.g., hemangiomas), skin tags, or pigmentary abnormalities. These features may be subtle but are strongly associated with occult spinal anomalies and necessitate further investigation. Our article review revealed a broad consensus that isolated, simple sacral dimples—defined as lesions less than 5 mm in diameter, located within 2.5 cm of the anus, located strictly midline, and lacking any additional cutaneous findings—do not warrant further imaging [3,4,15-21]. Conversely, atypical dimples, such as those that are large, multiple, deep, highlying, or off-midline, as well as those associated with additional cutaneous stigmata (e.g., subcutaneous lipoma, hypertrichosis, hemangioma, skin tags, or deviated gluteal cleft), require further investigation. The risk of occult spinal dysraphism is particularly elevated when 2 or more stigmata coexist [3,4,15,16,18,21,22] (Table 2). The careful evaluation of both physical examination and targeted imaging findings allows the timely identification of clinically significant cases among infants with sacral dimples while avoiding unnecessary imaging in those with benign, isolated lesions.

Imaging

A stepwise diagnostic approach to suspected spinal dysraphism should be guided by evidence-based criteria to determine the need for imaging. Spinal ultrasonography is widely recommended as the initial screening modality for infants with atypical sacral dimples, particularly those younger than 4–6 months of age, before ossification of the posterior elements limits acoustic windows [5]. It is favored as an initial tool because of its high sensitivity and specificity (both approximately 96%) as well as its safety and cost-effectiveness (Fig. 4A) [5,23,24]. Nevertheless, recent evidence indicates that a routine ultrasonographic screening may not be necessary in cases of isolated, simple sacral dimples that lack high-risk cutaneous markers [3,21,23]. The feasibility of spinal ultrasonography in neonates is attributed to incomplete ossification of the posterior vertebral arch, a normal feature of infancy, and the osseous defects seen in spina bifida, both of which allow sound wave penetration and adequate visualization of the spinal canal [25].

For patients with fewer than 2 of the following—cutaneous stigmata, atypical dimples, or gluteal cleft deviation—lumbar ultrasonography during the first month of life is advised, with subsequent magnetic resonance imaging (MRI) reserved for cases in which abnormalities are detected. Conversely, in infants presenting with a neurological or orthopedic impairment, multiple cutaneous stigmata, or specific high-risk markers such as dermal sinus, a human tail, or subcutaneous lipoma, MRI should be performed directly given the elevated risk of spinal dysraphism [3]. When an additional evaluation is warranted, MRI offers superior anatomical detail, particularly for assessing the level of the conus medullaris; the thickness and morphology of the filum terminale; tethering lesions; and associated bony dysraphic anomalies [26]. Prone MRI can be considered in select cases, such as patients with prior tethered cord release or high clinical suspicion despite normal findings on supine MRI. However, prone imaging offers limited additional diagnostic value if abnormalities are already evident in standard supine MRI studies [27]. MRI in infants and young children often requires sedation; beyond the risk of sedation failure, complications such as bradycardia and hypotension reportedly occur in 3%–8% of cases, underscoring the need for careful consideration when performing the examination [28,29].

In cases in which imaging is pursued, the interpretation of conus medullaris position is crucial. A conus terminating at or above L2–3 is considered within normal limits at any age. In contrast, termination at L3–4 or below is generally considered abnormal, although conus at L3 may be a normal variant in neonates younger than 6 months. Accordingly, any interpretation should be contextualized based on patient age and overall clinical presentation [10]. A low-lying conus below the L2 vertebral body is commonly associated with tethered cord syndrome [26,30]; however, tethering can occur even when the conus is in a normal anatomical position [31]. In the diagnosis of tight filum terminale syndrome, 2 radiographic features are particularly important: a low-lying conus medullaris, typically terminating below L2 (although as low as the upper border of L3 may be acceptable in younger infants), and a thickened filum terminale, usually measuring greater than 2 mm in diameter. This thickening is frequently accompanied by fatty infiltration, further supporting the diagnosis of filar lipoma. When these features are present, especially in conjunction with suggestive clinical findings, tethered cord syndrome should be strongly considered [31,32].

The imaging findings of conditions that may be associated with a sacral dimple are as follows (Table 3). Lipomyelomeningocele typically presents as subcutaneous fat tethering the cord that poses a risk for tethered cord syndrome. T1-weighted MRI shows fat signals that are otherwise suppressed on fat-saturated sequences, with a low-lying conus and a deformed, tethered neural placode. Although lipomyelomeningocele is rare, its early recognition is crucial to preventing neurological deterioration (Fig. 4B) [33]. Dermal sinus tracts are epithelial-lined tracts that may extend to the spinal cord and carry a significant risk of infection, including meningitis. A tethered cord is present in approximately 62.5% of cases and often accompanied by a thickened filum, and the tract may be directly visualized on MRI [34]. Conus lipomas are frequently encountered and often tether the cord, with anatomical variations that can complicate their surgical management. They appear as T1 hyperintense masses in the low-lying conus and are sometimes associated with syringomyelia or sacral agenesis [35]. Similarly, filar lipomas are common findings, appearing as fat signals (>2 mm) within the filum terminale that can cause tethering or be incidental [36]. A tight filum terminale may impair normal ascent of the conus and is often associated with other spinal malformations. Imaging typically demonstrates a thickened filum (>2 mm) with a low-lying conus, while dynamic MRI can reveal restricted filar motion [37].

Split cord malformations present with 2 hemicords separated by a septum that may be bony (type I) or fibrous (type II), be linked to sacral dimples, and tether the cord through the septum [38]. Dorsal dermal sinuses are tracts leading to the spinal canal and often associated with inclusion tumors such as dermoid or epidermoid cysts. On MRI, they appear as thin hypointense stripes on sagittal images, with potential visualization of associated cystic components [37]. Dermoid cysts, typically benign midline masses, can be associated with dermal sinuses and may become infected. Moreover, they demonstrate T1 hyperintensity with variable T2 signals; if infected, dermoid cysts may exhibit restricted diffusion or peripheral ring enhancement [39].

Other lesions, such as open myelomeningocele, myeloschisis, and diastematomyelia, are usually apparent on visual inspection and do not require direct discussion in connection with sacral dimples.

Persistent terminal ventricle

Historically known as the “fifth ventricle,” the persistent terminal ventricle (PTV) is a small, ependyma-lined cavity located within the conus medullaris (Fig. 5). While it is often observed in postmortem examinations, it is only detectable on MRI once it reaches a certain size. Embryologically, PTV results from incomplete regression of the terminal ventricle during secondary neurulation that retained continuity to the central canal of the spinal cord. PTV is typically asymptomatic, but there have been rare cases of marked cystic enlargement associated with symptoms such as low back pain, sciatica, and bladder dysfunction. It remains uncertain whether these symptomatic enlargements represent developmental variants or acquired pathological changes due to obstruction within the terminal ventricle. Radiologically, PTV can be distinguished from hydromyelia by its distinct location just above the filum terminale and from intramedullary tumors by the absence of contrast enhancement on gadolinium-enhanced MRI. Notably, cystic structure size typically remains stable on follow-up imaging studies [37].

Treatment

A particular challenge in pediatric patients is that neurological assessments may be limited due to incomplete development; moreover, treatment decisions are made not by the patients themselves but by their parents or other surrogates. Indeed, a survey of neurosurgeons regarding surgery for sacral dimples reported that the decision to operate as well as its timing was often influenced by parental preferences [17]. Nevertheless, when objectively describing the surgical procedure and its outcomes, surgical decision-making for occult spinal dysraphism is strongly influenced by both the level of the conus medullaris and the presence of associated filar pathology [17].

Tethered cord syndrome, when left untreated, tends to follow a progressive course, with gradual worsening of neurological, urological, and orthopedic functions. Thickening of the filum terminale is an important radiologic marker for tethered cord syndrome, although the definition of “thick” varies across studies. Most of the literature has used a cutoff of >2 mm, whereas a recent ultrasonographic study proposed 1.1 mm as the optimal threshold for screening filar lipomas [40]. In one study, the incidence of a prominent filum terminale was 11.3%, and thick filum terminale (>2 mm) was 2.2% [2].

Surgical detethering, the mainstay of treatment, aims to relieve traction on the spinal cord and cauda equina, thereby preventing further neurological deterioration and, in many cases, improving or stabilizing existing deficits. Various surgical approaches are available, including filum terminale transection, debulking of associated lesions, or a combination thereof [41,42]. Filum terminale transection has gained favor as the initial procedure for tethered cord syndrome due to its relatively short operative time, minimal invasiveness, and high symptomatic relief rate. However, a significant concern with this approach is the relatively high rate of retethering of approximately 50% [43,44]. An alternative approach is spinal-shortening osteotomy, which reduces longitudinal tension on the spinal cord by surgically shortening the vertebral column. This method may be particularly beneficial in patients who experienced prior untethering procedures complicated by retethering, as it lowers the risk of postoperative cerebrospinal fluid leakage and epidural scarring, 2 key contributors to recurrent tethering [45-48].

When a dermal sinus tract is present, complete surgical excision is recommended to eliminate potential infection into the spinal canal. Intraoperatively, these tracts may be found in continuity with tethering elements such as a thickened filum terminale, intradural lipoma, abscess, or even direct adherence to the spinal cord. Operative microscope guidance is critical in safely excising the tract and addressing any associated tethering elements [34].

In cases of lipomyelomeningocele, surgical goals include decompression and detethering by resecting the adipose mass, identifying and releasing the tethering fascia or filum terminale, and preserving the functional integrity of the neural elements. However, the optimal surgical timing remains under debate. Although some clinicians advocate for early prophylactic intervention—prior to the onset of neurological symptoms—others suggest delaying surgery until signs of dysfunction emerge. Nonetheless, evidence indicates that up to 40% of affected infants show neurologic, orthopedic, or urologic abnormalities at birth and that progressive deterioration is likely in many untreated cases. Thus, early surgery is often favored with the primary objective of preventing long-term deficits [33].

Surgical management of conus or filar lipomas varies in extent from sub- or near-total resection to “maximal safe resection” depending on lesion characteristics and surgeon preference. For filar lipomas, microsurgical exposure via a limited laminectomy and midline durotomy is followed by identification and careful dissection of the lipomatous filum terminale. Confirmation of the absence of neural elements within the filum is essential prior to resection and is typically achieved using alternating cauterization and cutting techniques to minimize bleeding and adhesions [35,49].

In cases of tight filum terminale, intraoperative neuromonitoring with somatosensory-evoked potentials is common [44]. This aids accurate filar identification and helps prevent inadvertent damage to adjacent nerve roots. Once isolated, the filum is transected under microscopic visualization and dural closure is performed to prevent cerebrospinal fluid leakage and reduce the risk of adhesion-related retethering [50].

Split cord malformations are typically managed surgically when associated with neurological symptoms or tethering. Historically, conservative management was the mainstay of treatment because of concerns over surgical risks, particularly in asymptomatic individuals. However, in the 1980s, a shift occurred toward early surgical intervention to prevent progression. More recent studies offer conflicting perspectives. Although some reports support the early resection of spinal lipomas associated with the conus, European studies raised concerns about postoperative deterioration, even in prophylactically treated patients [51-53]. A more aggressive resection technique proposed by Pang [54] showed promising long-term outcomes with high neurological preservation and minimal progression rates in previously asymptomatic patients [54]. Nonetheless, the decision to operate in asymptomatic cases remains controversial and should be individualized [55].

Prognosis

A simple sacral dimple is typically considered a benign dermatological variant; in the majority of cases, it is not associated with underlying spinal abnormalities or neurological dysfunction. However, sacral dimples are occasionally cutaneous markers for occult spinal dysraphism, including tethered cord syndrome, dermal sinus tract, lipomyelomeningocele, and other malformations. The prognosis in these cases varies depending on the specific pathology, diagnostic timing, and interventional timeliness.

Among sacral dimple–associated anomalies, tethered cord syndrome has been studied most extensively. The neurological prognosis is closely linked to spinal cord tethering severity and duration. Progressive traction may lead to symptoms such as back or leg pain, lower-extremity weakness, paresthesia, and bowel or bladder dysfunction. If left untreated, these symptoms tend to worsen over time, with a higher risk of irreversible deficits including urinary incontinence and motor dysfunction. Notably, greater mechanical strain on the spinal cord has been associated with earlier onset and more rapid progression of symptoms [56-58].

The efficacy of early surgical intervention has been demonstrated even in patients with a normally positioned conus medullaris. As released by Warder and Oakes [59], 12 patients with a normal-level conus underwent filum terminale transection. Despite varying combinations of neurological signs, cutaneous markers, and structural anomalies, postoperative improvement was observed in a substantial proportion of patients: 75% in bladder function, 100% in bowel function and paresthesia, 75% in motor weakness, and 67% in pain. Similarly, a retrospective review by Kulwin et al. [60] of 16 patients—most with syringomyelia and abnormal urodynamic profiles—found that all 11 patients who underwent follow-up urodynamic testing demonstrated improvement. Additionally, the majority of those with back or leg pain, gait disturbances, or bowel symptoms reported subjective postoperative relief. Among patients with scoliosis, the outcomes were mixed, though 2 of 3 demonstrated disease stability or improvement.

In contrast, dermal sinus tracts, while sometimes asymptomatic, carry a significant risk of central nervous system infection, particularly meningitis, due to their potential communication with the intradural space. Complete surgical excision is associated with a favorable prognosis, especially when performed prior to the onset of complications.

The prognosis of lipomyelomeningocele remains controversial, particularly in terms of optimal surgical timing. Although the diseases of some asymptomatic patients may remain stable, longitudinal data suggest that a substantial proportion will eventually experience neurological deterioration. Many experts advocate for early surgical intervention to prevent irreversible deficits. However, decisions should be individualized, especially in the absence of clear predictors of progression.

For conus and filar lipomas, the approach is similarly nuanced. Aggressive resection strategies, such as those proposed by Pang [54], have demonstrated excellent long-term neurological outcomes with low recurrence rates. Nevertheless, some asymptomatic cases managed conservatively have also remained stable, underscoring the need for a risk-benefit analysis tailored to each individual.

Last, the prognosis of split cord malformations depends largely on the presence of symptoms. Asymptomatic patients may be observed, while those with neurological effects benefit from surgical intervention. Outcomes are generally favorable if treatment is performed before irreversible damage occurs.

Conclusion

While most sacral dimples are benign and not clinically significant, they are occasionally cutaneous markers of underlying spinal anomalies with potential neurological consequences. Thus, a thorough understanding of clinical assessment criteria and appropriate imaging indications is essential to accurate evaluations. When pathology is present, early recognition and timely intervention are critical to optimize neurological outcomes. Differentiating between innocuous findings and those suggestive of occult spinal dysraphism requires careful clinical judgment, emphasizing the importance of a systematic and evidence-based approach when evaluating infants with sacral dimples.

Footnotes

Conflicts of interest

No potential conflict of interest relevant to this article was reported.

Funding

This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Author contribution

Conceptualization: JE, KSL, SHY; Methodology: JE, SHY; Writing and editing: JE, SHY; Resources: KSL; Visualization: KSL; Writing - original draft: JE, SHY; Writing - review & editing: SHY

Fig. 1.

Normal sacral dimple.

Fig. 2.

Spinal ultrasonography and magnetic resonance images of sacral dimple showing no evidence of underlying spinal abnormalities.

Fig. 3.

Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) flow diagram of the literature selection process. Following a PRISMA-guided search and screening process, the articles identified in PubMed were subjected to title/abstract and full-text evaluations and included or excluded per priori criteria.

Fig. 4.

Imaging findings of lipomyelomeningocele in 2 patients. (A) Spinal ultrasonography image showing a fistulous tract extending from the skin’s surface to the spinal canal (bottom arrow). The conus medullaris is tethered and extends down to the sacral level. A focal cystic lesion is observed at the L5–S1 level (top arrow). (B) Preoperative sagittal T1-weighted magnetic resonance image showing a high-signal-intensity mass located dorsally within the intradural space at the L2–4 levels. The conus medullaris is lowlying with a cord-like fat signal extending along the filum terminale (arrow). No significant vertebral defect or dural ectasia is visible. Postoperative imaging (far right) shows resolution of the intradural mass.

Fig. 5.

Sacral dimple with ventriculus terminalis. Spinal ultrasonography image demonstrating a sacral dimple and fusiform dilatation of the distal central canal consistent with the ventriculus terminalis (arrow). No evidence of a tethered cord or other spinal anomalies is visible.

Table 1.

Classification of spinal dysraphism based on embryological mechanisms and morphologic characteristics

Type	Lesion	Developmental mechanism	Key features
Open (aperta)	Spina bifida aperta	Failure of primary neurulation (neural tube closure)	Exposed neural tissue due to incomplete closure
	Spinal meningocele	Completed neurulation, failure of mesenchymal closure	Herniation of meninges through vertebral defect
	Myelomeningocele	Failure of primary neurulation with neural element herniation	Spinal cord and meninges herniate through defect
	Myeloschisis	Complete failure of closure	Exposed, unfused neural plate without covering
	Split cord malformation (hemimyelomeningocele)	Combined failure of neurulation and notochord canalization	Split cord with associated open lesion
Closed (occulta)	Thickened filum terminale	Abnormal regression after secondary neurulation	Low-lying conus, tethering without skin defect
	Dermal sinus	Incomplete disjunction of neuroectoderm and surface ectoderm	Epithelial tract from skin to neural tissue
	Lumbosacral lipoma	Abnormal mesodermal differentiation after neural tube closure	Fatty tissue extending into the spinal canal
	Lipomyelomeningocele	Disruption during secondary neurulation	Neural elements mixed with fat, protruding
	Split cord malformation	Persistent accessory neurenteric canal	Dual hemicords with septum (bone/fibrous/cartilage)
	Neurenteric cyst	Failure of separation between endoderm and notochord	Cystic lesion along the spinal axis

Table 2.

Red flags for sacral dimple

Red flag finding	Clinical description
Large	More than 5 mm in diameter
Multiple	Presence of more than one dimple
Deep	The base is not identified
High-lying	More than 2.5 cm from the anus
Off midline	Located away from the central axis of the spine
With additional stigmata	Cutaneous: subcutaneous lipoma, hypertrichosis, hemangioma, skin tags, deviated gluteal cleft
With additional stigmata	Other congenital disease

Table 3.

Conditions and imaging findings associated with sacral dimple

Condition	Clinical importance	Typical findings
Lipomyelomeningocele	Subcutaneous fat tethering; risk of tethered cord	Fat signal on T1, low conus, deformed neural placode
Dermal sinus tract	Tract to cord; infection (meningitis) risk	Tract visible; tethered cord (~62%); thick filum
Conus lipoma	Often tethers cord; anatomical complexity	T1 hyperintense mass in conus; low conus; possible syrinx
Filar lipoma	Common; may tether or be incidental	Fat signal (>2 mm) in filum; variable conus level
Tight filum terminale	May impair conus ascent	Thickened filum (>2 mm), low conus, restricted motion
Split cord malformation	May tether via septum; associated dimples	Two hemicords separated by bony/fibrous septum
Dorsal dermal sinus	Tract to canal; often with dermoid/epidermoid	Thin hypointense tract; possible inclusion tumor
Dermoid cyst	Benign; can be infected	T1 hyperintense mass; T2 variable; possible ring enhancement

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