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].

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.

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.

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.

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.

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].

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].

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.

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.